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Etronic
11-07-2012, 12:34 PM
Hi all

I need to make this.

Hi
I'm looking to use the LM386amp with a sensitive mic with automatic gain
From 20 to 200. The output will need to have enough single for
the next stage,the HT9170 chip to pick-up the single.
Does anyone have a working schematic that i could use for my application.
With the LM386 amp.And how do i get a automatic gain from 20 to 200
with low noise.

kindly appreciate your help.

Ron H
11-07-2012, 02:50 PM
Maybe you can get enough gain from the HT9170 op amp to avoid needing a preamp. How much signal are you getting from the microphone?
Why do you think you need AGC?

BTW, 'single' means 'one'. The word you want is 'signal'.:)

Etronic
11-09-2012, 04:12 AM
Hi Ron

I making a remote security dtmf electronic lock opener.At a
range of 10FT.I need the AGC to get enough pickup.The HT9170 will not pick it up at that distance.I'm assuming a gain of 20 to 200 will be enough. Until i test it.

Ron. Do you or can you provide me with a schmatic that will work,with a LM386 with AGC or aother preamp.

Ron H
11-09-2012, 04:39 AM
I don't think you need AGC. I think you can use a fixed-gain preamp, followed by a lowpass filter, then a high gain limiter (such as a comparator with a little hysteresis). Feed the square wave output of the limiter to the HT9170. This is much simpler than an AGC circuit.
I believe the HT9170 will work fine on square waves. You could easily test it on the bench before you design and build the preamp and filter.

Etronic
11-14-2012, 12:30 AM
http://howcircuits.com/lm358-preamp.html
Ron

can you provide me with a schematic of preamp plus filter and limiter So i have something to build.I'm not an engineer.TL071amp,LM358amp,might
work as the preamp.What would you use or recommend.About the filter
no idea what or how to build one.And what comparator to use.

I found the above link on a 358.Will this do. Will i need to add or change any parts
in that circuit.Or would the TL071 circuit work better. link below.


http://www.elektropage.com/default.asp?tid=556

Ron H
11-14-2012, 01:19 AM
Do you have to run the op amp on a 5V supply, or do you have dual supplies available? if so, what voltages can you use?

Etronic
11-18-2012, 10:16 AM
Ron

I have either single supply voltage of 3.3V or 5V i need to use.I perfer 3.3V.

Audioguru
11-18-2012, 01:09 PM
The LM358 preamp uses the opamp as an inverting amplifier that has a very low input resistance of 1k ohms that attenuates the signal from the mic. The opamp should be a non-inverting amplifier with a fairly high input resistance.
The LM358 is too noisy to be a mic preamp. Use an audio opamp instead.
An LM358 is a dual opamp, a single opamp should be used instead.

The preamp with the TL071 audio opamp has the polarity of its HUGE 10uF input capacitor backwards and does not have biasing for an electret mic.
The 10uF capacitor passes earthquake frequencies as low as 0.68Hz.
For an audio response down to 20Hz the input capacitor should be a 330nF non-polarized film capacitor instead.

The minimum supply voltage for a TL071 is 7V so it can't be used with your 3.3v or 5V supply.

Ron H
11-21-2012, 03:17 AM
Here is an automatic gain-controlled amplifier that simulates well. With the level control set at 3.37V, the output will be ≈2V p-p, when the input is between 10mV and 100mV p-p.
The 2N5460 is available at Jameco (http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&search_type=jamecoall&freeText=2N5460)
MCP6401 is made by Microchip. It is available from several vendors.
The MCP6401 is a rail-to-rail I/O, low-noise op amp. You may not need the low noise feature.

Ron H
11-24-2012, 04:31 AM
I drew the boxes to highlight the functions of the various parts of the circuit.

See VCA810 (http://www.ti.com/lit/ds/sbos275f/sbos275f.pdf). Fig. 32 is an AGC amplifier.

Audioguru
11-24-2012, 04:44 PM
The microchip opamp might be too noisy (hiss) to be a mic preamp.

What do you have that produces DTMF tones that are heard as far away as 10 feet?

rogs
11-24-2012, 05:08 PM
I believe the HT9170 will work fine on square waves.

Sadly, not true. Although the chip itself actually 'squares off' the input internally, to present a better 'control' signal to the internal counters, this has to occur after the input band pass filters have split the signal into 'hi' and 'lo' group component signals.

If you 'clip' the incoming signal before these input filters, you will get a lot of false decoding. I made that mistake myself, some years ago! :)

The HT9170 (which is only an MT8870 clone) has quite an impressive input range -- almost 30dB, IIRC, so AGC is probably not necessary either.

As Audio Guru has pointed out, use a low noise audio op-amp, like the TLO71, to provide your initial mic gain. You can also use the internal op-amp in the HT9170, to provide a little extra gain, if necessary, but I suggest keeping the gain of that down to less than 10.

You really don't want to clip the signal before it reaches those internal band split filters.

Even with the system set up correctly to accept audio over your required range, you do need to make sure the system is only used in a reasonably quiet acoustic environment. Too much background noise will introduce artificial '3rd tones' into the signal, which will then be rejected by the decoder......

Ron H
11-25-2012, 12:23 AM
Sadly, not true. Although the chip itself actually 'squares off' the input internally, to present a better 'control' signal to the internal counters, this has to occur after the input band pass filters have split the signal into 'hi' and 'lo' group component signals.

If you 'clip' the incoming signal before these input filters, you will get a lot of false decoding. I made that mistake myself, some years ago! :)

The HT9170 (which is only an MT8870 clone) has quite an impressive input range -- almost 30dB, IIRC, so AGC is probably not necessary either.

As Audio Guru has pointed out, use a low noise audio op-amp, like the TLO71, to provide your initial mic gain. You can also use the internal op-amp in the HT9170, to provide a little extra gain, if necessary, but I suggest keeping the gain of that down to less than 10.

You really don't want to clip the signal before it reaches those internal band split filters.

Even with the system set up correctly to accept audio over your required range, you do need to make sure the system is only used in a reasonably quiet acoustic environment. Too much background noise will introduce artificial '3rd tones' into the signal, which will then be rejected by the decoder......Yeah, I rethought my ideas and came up with the same conclusion. That's why I designed and posted a circuit (that has too many parts) with low harmonic distortion.
Regarding the op amp, the OP requested a gain of 20 to 200. In my circuit, the output voltage is ≈2V p-p. When the gain is 200, the input will be ≈10mV p-p. I don't think op amp noise will be an issue with that input level. I do think a low-noise preamp will be required. In fact, I wonder if DTMF can be picked up by a mic from 10 ft away and decoded, unless the source of the DTMF tone is pretty darned loud.

Audioguru
11-25-2012, 02:02 PM
I was using a DTMF generator i found on the internet to generate the
tone sounds.From my computer.
Were the tones produced from fairly loud computer speakers?

The MCP6401 amp has .... low noise.
Audio Guru stated it will hiss.
How would it hiss if it states its a low noise amp?
The datasheet does not say low noise.
Its noise is much higher than a TL071 low noise opamp:

rogs
11-25-2012, 04:50 PM
To keep it simple, use an LMV358 op-amp. It's not especially 'low noise' but it's fairly modern, so at 33nV/vHz it's not bad. (TLO71 is 18nV/vHz by comparison). It also works from a 3.3V supply.

Using the circuit you linked to here: http://howcircuits.com/lm358-preamp.html


- Substitute the opamp for the LMV358

- make both C1 and C2 0.1uF

- make R2 4.7K

- omit R3 and R4, and connect pin 3 directly to pin 1 (and/or) 4 of the HT9170

- make R5 a 10K pot

- make the input resistor to pin 2 of the HT9170 10k, and connect C2 directly to that resistor

- keep the feedback resistor between pins 2 and 3 of the HT9170 as 100k

That will give you a gain range up to 200.

Because you are using an electret mic capsule, that will be the dominant 'noise' generator, so that's why an especially low noise op-amp is not so important in this case. The LMV358 will be fine.
Most modern electret capsules are OK, but I can recommend the Panasonic WM61A (which you can find on Ebay, or at Digikey). That's a pretty quiet device.

Ron H
11-25-2012, 09:33 PM
Rogs, did you slip a decimal point? R5/R2 goes from 0 to 2. The gain of the HT9170 is fixed at 10. That's gain range of 0 to 20.
I'm pretty sure that Etronic will remind you that he wants AGC (although I fail to see why he needs it).

THE_RB
11-25-2012, 10:03 PM
...
I making a remote security dtmf electronic lock opener.At a
range of 10FT.I need the AGC to get enough pickup.The HT9170 will not pick it up at that distance.I'm assuming a gain of 20 to 200 will be enough. Until i test it.
...

I think you need to re-think your "security" door lock!

If the door lock is opened by someone using a DTMF audible sound from any distance like a few feet, the security is totally compromised because the bad guys could just record the DTMF sound with a hidden device (like something with an auto-gain amp) and open the lock later using the recording. ;)

rogs
11-25-2012, 11:29 PM
Rogs, did you slip a decimal point? R5/R2 goes from 0 to 2. The gain of the HT9170 is fixed at 10. That's gain range of 0 to 20.
I'm pretty sure that Etronic will remind you that he wants AGC (although I fail to see why he needs it).

My bad -- sorry! Yup, the pot should be 100K not 10K. Variable gain of the first stage up to 20 (well, 21.28 actually!:)), second stage fixed at 10.

Thanks for that.

Not sure what any AGC is likely to achieve? (apart from 'hunting down' to max gain, and pick up noise!)

The input range of 'valid' DTMF signals for the HT9170 using a 3.3V supply is 30dB. (-36 to -6 dBm).
That's a pretty useful input signal range - in fact, better by some 10dB than your required '20 to 200' range (which is only a range of 20dB) - without making life more difficult with AGC, that would probably do more harm than good!:)

Ron H
11-27-2012, 04:49 PM
rogs

Thanks!

I will set the circuit up as noted.Once i receive the parts.
I will be back.

I thought about the AGC. As you guys stated i don't need it.
And just more added part to the circuit which i don't
want either. A variable pot gain will do.I just will need to
set the gain as needed.It seems that many people who ask for help have already decided what they need, and want help designing it, only to discover later that that a simpler approach will work. If you had been more forthcoming about your requirements in your first post, I would not have wasted my time designing an AGC amp. My bad for not dragging the details from you before I started designing.
It is always better to post too much info, rather than too little.
I am not asking for an apology. I'm just venting.

rogs
12-03-2012, 11:26 PM
I've not had any experience with those particular devices, but from the published data sheets they would appear to be fine. In fact, they appear to have a much higher spec than the op-amps we have been suggesting so far, so the only unknown would be with layout and supply decoupling.
The higher frequency specs might mean you need to pay special attention to those details, and follow good supply de-coupling practice, to prevent any unwanted oscillations.
That may not be a critical problem ---- as I say, I've not used these devices....

You do need to remember that an 'ultra' low noise op amp is not going to make a big difference to your project here, so opamps like the LMV358 would be fine in this application.
You are going to be using an electret mic capsule, which means that the internal premap within that mic capsule will be the defining noise source.
You are, however, expecting to pick up your signal from quite a distance, so the room ambient noise will also be a major factor here - even in a 'quiet' room!
So we're not dealing with a 'pro' level of low noise audio pre-amp here...... most modern op-amps, with the required 3.3V supply capability will probably be fine....

Audioguru
12-04-2012, 01:35 AM
The LMV358 is the noisiest opamp I have ever seen ("heard").
I am glad that they removed the crossover distortion from the original LM358.
Because its supply voltage is so low then its slew rate allows output up to 80kHz. The original LM358 had trouble above only 2kHz.

Audioguru
12-04-2012, 02:42 AM
I have never used an opamp on a supply as low as only 3.3V so I don't know about any low noise, low voltage opamps.

rogs
12-04-2012, 05:42 PM
I'll leave it to Audioguru to advise you on the best way forward......

Audioguru
12-04-2012, 06:35 PM
I'll leave it to Audioguru to advise you on the best way forward......
Sorry.
I have never used an audio circuit with a supply as low as 3.3V.

rogs
12-04-2012, 06:48 PM
Sorry.
I have never used an audio circuit with a supply as low as 3.3V.

The only one I have used at 3.3V - as an simple audio pre-amp for an electret mic - is the LMV358, which you have advised this chap is not suitable.

Although it is clearly not a good choice for a high quality low noise mic preamp - especially for use with dynamic mics - I felt it might well suffice here?

You disagree, and all we are doing is confusing this chap. So I'll step aside, and leave further advice in your more experienced hands.

No point in confusing the OP unnecessarily!....:)

rogs
12-05-2012, 08:24 AM
Certainly give it a try.

I suspect Audioguru was looking at the data sheet for the Texas Instruments version of the LMV358, rather than the much better version made by Fairchild Semiconductor. (National)....

Audioguru
12-05-2012, 01:56 PM
I suspect Audioguru was looking at the data sheet for the Texas Instruments version of the LMV358, rather than the much better version made by Fairchild Semiconductor. (National)
National was bought by TI recently.
The spec's should all be the same except Fairchild got a nOOb kid to wrongly make their datasheet graph of the noise voltage.

rogs
12-05-2012, 02:26 PM
As I said before, I defer to your greater experience....I simply do not have the expertise to know which manufacturers data sheets are right, and which are wrong.

I just use the devices, and comment on how I find them for a particular task, in practice.

Using a 3.3V supply for an audio project is something I've only done once before....

The LMV796 that the OP suggested earlier in the thread looks to be a lot better, noise wise, and retains the low voltage and rail to rail output capability. But I've never used one... so whether it has any other 'quirks'. I simply don't know....

Audioguru
01-16-2013, 11:08 PM
Read my first paragraph in my post #8 about the problems with that horrible mic preamp circuit.
An LMV796 opamp in that circuit will do almost the same.

The mic preamp opamp should be non-inverting so it has a fairly high input impedance that does not attenuate the signal from the electret mic.

Audioguru
01-17-2013, 03:13 AM
Sorry but it seems that you do not know the basics of electronics.
I will help you if you tried but you do not know enough to even begin to try.
Maybe there is a teacher here who can help you.

Audioguru
01-17-2013, 03:19 AM
Deleted my double post.

tshuck
01-17-2013, 11:36 PM
Audioguru

If you can't help then don't.And don't post in my theads anymore.
And you haven't help me anyway,So i don;t need you to help me.
All you do is dis poeple who need help.What help have you given me.
There more poeple on here who have help me then you ever will.

<SNIP>

I may be only 13 and starting out in this field of electronics. I do know some basics. but not in audio.

You come on here and dis everyone. So for the second time KISS MY ASS>
I haven't been a part of this thread yet, but this really angered me.

Please, please do not drag this respectable forum through the mud with your slander!

I don't care if your are 13 or 113, that is no excuse to act like a spoiled brat. People here are trying to help you and THAT is all you have to say.

If you are so aggravated by the lack of progress, perhaps you should learn these concepts on your own instead of belaying such a small attitude.

I haven't offered help because I work in digital electronics, however, Audioguru's name does him justice, he knows his stuff, so show a little respect.

tshuck
01-18-2013, 03:09 PM
Who care's if my statement angered you
Who's spoiled Brat. Not me.
case and point.

Good luck on your problem. You will be ignored by me henceforth...feel free to rant about me. I won't see it.

Georacer
01-18-2013, 06:45 PM
This is a borderline ban situation.

@Etronic
Please understand that this is a quite large forum and many different people come and go. If you see something you don't like, try to ignore it. If you see something that offends you, please report it via the http://forum.allaboutcircuits.com/images/buttons/report.gif mark at the top of the post.

However, there are some members that daily spend a large amount of time trying to help other members and are backed up by knowledge, experience and consistency. These members form the core of AAC and as a result have our respect.

In your case, Audioguru might have dropped in with no help, but you answered with swears and profanity. This, automatically, puts you in the wrong side, despite of any arguments of yours.
Firstly we establish a civil environment where we can discuss and then we will hear any arguments.

This is the second time you curse other members. On the third, a ban will be issued. Be warned.

Audioguru
01-22-2013, 02:11 AM
The datasheet for the opamp you are using shows inportant parts that are missing in your circuit:
1) A voltage divider using RB1 and RB2 to bias the input of the opamp at half the supply voltage.
2) An input capacitor to prevent power to the electret mic from messing up the bias voltage.
3) A capacitor in series with the feedback resistor to ground to prevent the opamp from amplifying the DC bias voltage.

Audioguru
01-22-2013, 12:31 PM
You must use a little arithmatic to select correct values of resistors and capacitors.
Your circuit has a gain of only 1 at high audio frequencies and it attenuates low audio frequencies.

Audioguru
01-24-2013, 03:53 AM
Is 200K enough for rb1 and rb2 for the the biasing of the opamp?
I can't remember which opamp you are using. Its datasheet says what is its maximum input bias current. Use 10 times the current in RB1 and RB2.

I changed some values on the opamp.
The low frequency cutoff is created by the 1k resistor in series with the 1nF capacitor which is 160,000Hz. Then 800kHz and higher will have a maximum gain of 21 and the maximum gain at 160,000Hz is 14.9. All audio frequencies will have a maximum gain of only 1.

I showed you the simple arithmatic to calculate it.
If the value of your 1nF capacitor is 1uF then 160Hz will have a maximum gain of 14.9 and only some DTMF frequencies will not be detected.

The lowest DTMF frequency is 697Hz. Then the cutoff frequency of your opamp should be 697/5= 139.4Hz or lower. If your 1nF capacitor is 2.2uF then the cutoff frequency will be 73Hz which is fine for DTMF.

Audioguru
01-25-2013, 01:35 PM
I know? But i can only use what i have in parts draw.
These are the only values i have.
.001,3.3uF,4.7uF,2pF,10uF Ceramic.
10uF,100uF,2.2uF Aluminum electrolytic. But? I heard these are to
noisy for audio. Is this true?
I said that the circuit will work fine if you replace your 1nF capacitor with 2.2uF. You have 2.2uF so use it.
Capacitors do not produce noise.

How did you come up with the number five divide by the low group 697Hz.
The level is reduced to 0.707 times at the cutoff frequency (but then DTMF might not work) but the level is almost flat at 697Hz if the cutoff frequency is 5 times less.

Was this base on the decoders output?
No, it is the required frequency response to the input of the decoder.
DTMF is two frequencies (a low frequency and a high frequency) and both must have almost the same level. The lowest frequency is 697Hz and the capacitor must have a high enough value so it is not attenuated compared to the level of the higher frequency.

There is no information in the LMV796 datasheet to calculate for 1RB and 2RB for biasing.The max input current is 100 fempto amps or 50pA at 1 volt. At 125degrees celius.Ambient Temperature.
That is what you needed to know. The maximum input bias current of only 50pA is extremely small so the value of RB1 and RB2 can be very high. 100k is fine.

Ron H
03-13-2013, 08:19 PM
Change the coupling cap between the op amp output and the decoder input to 1uF (or 2.2uF). You should also add a 100nF cap between the vcc and ground pins on the op amp, with leads as short as possible, to prevent oscillation. Otherwise, the circuit looks OK, assuming an overall gain <210 will be adequate.

Ron H
04-11-2013, 04:44 PM
Are you sure your microphone will work with such low voltage and current? Do you have a datasheet for it?
Why do you have 3 separate symbols for ground? Are they all connected to each other?
Do you have the negative terminal of your power supply connected to ground?

Ron H
04-15-2013, 03:55 PM
Do you have signal at the output of the op amp?
What pin are you monitoring on the HT9170?

Ron H
04-19-2013, 03:22 AM
It appears that you have swapped pins 4 and 5.

You need to add a 0.1uF cap between pins 2 and 5, after you get the wiring corrected.

I'm assuming that you are mounting the op amp upside down, also known as "dead bug".

Ron H
04-20-2013, 02:57 AM
Why did you post an inaccurate drawing for us to critique? Did you forget that you had made the error on the drawing?

Is the op amp mounted upside down, so that the orientation dimple is hidden?

You need to test the amplifier by applying a signal generator in place of the microphone.

WBahn
07-23-2013, 05:30 AM
Have you studied the data sheet for the HT9170?

Ramussons
07-23-2013, 01:09 PM
The terminals of the input opamp is clearly indicated. You can set the gain by selecting the feedback / input resistor combination.

Ramesh

Ron H
07-23-2013, 01:24 PM
Numerous sites explain how to calculate the closed loop gain of an op amp.
Study AAC's ebook chapter on op amps (http://www.allaboutcircuits.com/vol_3/chpt_8/1.html).
Here is a Wikipedia article about inverting amplifiers using op amps (http://en.wikipedia.org/wiki/Operational_amplifier_applications#Inverting_ampli fier).

Ron H
07-25-2013, 01:03 AM
Either the gain is set at gain of 10+1=11 or a gain of 10-1=-9
for the circuit in post 1 of the HT9170 circuit.Is this correct.if not
Please explain.

Gain = R1/R2+1Gain = -(Rf/Rs)=-(10k/1k)=-10.
See the links in post #5.

EDIT: corrected equation

rogs
07-25-2013, 11:14 PM
This HT9170 circuit. Can you tell me what is the gain set at.
And what resistor do i change to set the gain lower or
higher.Is it the 10Kohm connect to the 100kohm.
pins 2&3. How do i calculate for a gain of 1 to 20.


Gain is set to 10 (inverting mode).
To increase gain to 20 (actually 22) change 100K to 220K

To set gain to 1 change 100K to 10K.

Do not confuse yourself with the non inverting mode calculations you seem to be writing about.

Ron H
07-26-2013, 12:16 AM
http://www.allaboutcircuits.com/worksheets/opamp5.html
Question 11 in this link that you provided. In post #5 of my tread.

States voltage gain for feedback divider for non-inverting op-amp.

Is Av=R2/R1+1


But in the circuit i posted in post #1 the only two resistor are
the 10k thats connected to pin2 and the 100k that connected
to pins 2&3. Do these set the gain for the HT9170 decoder IC.

yes or no if no then how do i set the gain for this part.Sorry, I screwed up in post #8. I have corrected it. It now shows the correct equation for the inverting amp, which is what you have in your schematic.

Ron H
07-26-2013, 07:51 PM
inverting amp input is on the HT9170.

Ok! You are right.About the amp But? the audio amp.That was posted
in the original tread that closed.I just left that audio amp part out in post one of this tread.So not to be confuse on the two circuits.

I Enclosed the two Circuits together.Which i got the audio part to work correctly.Since i posted in the original thread that closed.

Im trying to understand all this.Circuit by circuit.Its confusing:confused: since
my original thread had more of the circuits.info.The input amp has a gain of (1+R2/R1), so, with R2 being variable from 0 to 20k, and R1=1k, the gain of that stage can be varied from 1 to 21. Multiply that by the gain of 10 in the HT9170, and your overall gain can be varied from 10 to 210.

Ron H
07-27-2013, 07:29 PM
I like to know what can i do to prevent the LED from coming on
when i power up the circuit.I only want pin 15 to come on when
there is only a valid tone.Not when i power up the circuit.

Any idea. Eclosed circuit.How long does the LED stay on when you power up the circuit? Maybe we can design a fix for you.


Also what resistor values can i use for leds on pins 11-14. Im using 330ohms on pin15 will
the same value work or should i use a higher value say 1K.You can use the same resistors for all LEDs. See the table at the top of p.5 in the datasheet. The values for source and sink current are pretty low.

DerStrom8
07-27-2013, 08:04 PM
Just wanted to mention, if your thread is "closed" (not locked) due to inactivity, you can still post to it. You just have to click the little checkbox saying you understand it's old and want to post anyway, down at the bottom before actually posting.

EDIT: I just did this for you, your thread should be back. I'm wondering if the two threads should be merged, since they are regarding the same topic? http://forum.allaboutcircuits.com/showthread.php?t=76609&page=7

Whaddaya say, mods? :D

Regards,
Matt

DerStrom8
07-27-2013, 08:06 PM
Just resurrecting this for you, Etronic. Perhaps the moderators can merge them now?

Regards,
Matt

bertus
07-27-2013, 08:19 PM
Hello,

The other thread was never closed.
It only gave a warning for "old age".
You could still have answered by ticking the warning of "old age".

The thread can be merged, if wanted.
The posts will appear in timeline order.

Bertus

Etronic
07-27-2013, 11:10 PM
Just resurrecting this for you, Etronic. Perhaps the moderators can merge them now?

Regards,
Matt



Thank! For getting this back for me.

I ask Bertus to merge these two thread to become as one.

rogs
07-27-2013, 11:30 PM
I like to know what can i do to prevent the LED from coming on when i power up the circuit..

The MT8870 - or indeed any of it's 'clones', like the HT9170 - does not have a guaranteed 'power on' reset state integral to the chip.
Without either 'firing' a valid DTMF code into the analogue input, or adding extra power on reset logic, you cannot guarantee the state of any of the output pins on 'power up'.
You could disable the outputs by holding pin 10 'low', until a valid input code had been received, for example.

You'll need to explain what you need the device to do, in its initial 'power up' state?....

Edit: a similar query came up a couple of years ago on this forum.

Thee's a sketch attached to this post that may help:

http://forum.allaboutcircuits.com/showpost.php?p=217156&postcount=2

Ron H
07-28-2013, 12:37 AM
Here is a circuit that should keep the LEDs off for about 1 second after power up.

bertus
07-28-2013, 07:44 AM
Hello,

The threads are merged now.

@RonH,
The post numbering has changed during the merge process.
When referring back to a post number, the numbers of the second thread started by Etronic will be different.

Bertus

rogs
07-28-2013, 08:58 AM
Here is a circuit that should keep the LEDs off for about 1 second after power up.

The resistors connected to pins 11 thru 15 may well be 300Ω ( 330Ω is a more common value) - although trying to source something like 3mA from the output of an 8870 (or 9170) is pushing it a bit. (about 3 times the specified source current!)

The resistor connected to pin 16 will need to be more like 330KΩ. ( any value between 100KΩ and 470KΩ should work OK)

As Ron points out, this mod will ensure the LED connected to pin 15 will not 'pulse' on once during power up. (It will only come on thereafter when actually receiving a valid DTMF code pair).
The LEDs connected to pins 11 to 14 will power up in an unknown latched on or off condition without a 'power on reset' of the type described in my post linked to above.
The mod Ron describes will only keep them off for a second or so after initial power up.. They may well come on after that. You simply can't tell.

Ron H
07-28-2013, 02:55 PM
The resistors connected to pins 11 thru 15 may well be 300Ω ( 330Ω is a more common value) - although trying to source something like 3mA from the output of an 8870 (or 9170) is pushing it a bit. (about 3 times the specified source current!)I had pointed out the wimpy drive capability in post #84.

The resistor connected to pin 16 will need to be more like 330KΩ. ( any value between 100KΩ and 470KΩ should work OK)Etronic originally had a 300k there, but I thought it was attached to the resistor in series with the LED on pin 15, so I changed it to 300. My bad.:( I have edited the schematic I posted to restore it to 300k.

As Ron points out, this mod will ensure the LED connected to pin 15 will not 'pulse' on once during power up. (It will only come on thereafter when actually receiving a valid DTMF code pair).
The LEDs connected to pins 11 to 14 will power up in an unknown latched on or off condition without a 'power on reset' of the type described in my post linked to above.
The mod Ron describes will only keep them off for a second or so after initial power up.. They may well come on after that. You simply can't tell.Thanks for the clarification, rogs. I sorta figured that was the case.

Etronic
07-29-2013, 06:20 PM
You guys are awesome! Thanks.


Thats what i need.To prevent the Led on pin 15 from just coming on when i power up.Then it with run as usual.I just don't want a false reading
when theres no valid tone at power up.

I like to use Rons added circuit do to less parts and lower current draw from the Battery.Will either one do the same function.Rogs or Ron.

Should i keep the 300k or change it to 330K on the steering on pin 16.:confused:

I will use 200ohms on all Leds on pins 11-15 Or should i use 300ohms.
As ron post in circuit.

rogs
07-30-2013, 01:18 AM
If you are using a 3.3V supply rail, then to keep within HT9170 spec, you really need to use 1KΩ resistors in series with the LEDs on pins 11 thru 15.
(The device is only specified as being able to source about 1mA from those output pins).

You will probably need to use 'hi-bright' type LEDs. With only about 1.3V across the resistor (red, green or yellow LEDs will have about 2 volts across them, when turned on) you will not see 'standard' LEDs very well.
You can't use blue LEDS here - they need more than 3V across them.

There are 4 identical gates in a 4093. You can use them any order you wish. See the data sheet here for pin outs:

http://www.ti.com/lit/ds/symlink/cd4093bc.pdf

(Pin 14 VDD is +V (3.3V) and pin 7 is 0V (gnd) )

Use a 330KΩ for the pin 16 resistor. It will be easier to find than a 300KΩ resistor, and as I mentioned above, the value is not critical.

Ron H
07-30-2013, 01:32 AM
If you are using a 3.3V supply rail, then to keep within HT9170 spec, you really need to use 1KΩ resistors in series with the LEDs on pins 11 thru 15.
(The device is only specified as being able to source about 1mA from those output pins).

You will probably need to use 'hi-bright' type LEDs. With only about 1.3V across the resistor (red, green or yellow LEDs will have about 2 volts across them, when turned on) you will not see 'standard' LEDs very well.
You can't use blue LEDS here - they need more than 3V across them.

There are 4 identical gates in a 4093. You can use them any order you wish. See the data sheet here for pin outs:

http://www.ti.com/lit/ds/symlink/cd4093bc.pdf

(Pin 14 VDD is +V (3.3V) and pin 7 is 0V (gnd) )

Use a 330KΩ for the pin 16 resistor. It will be easier to find than a 300KΩ resistor, and as I mentioned above, the value is not critical.Rogs, can you link to the HT9170 datasheet that has output drive specs for vcc=3.3v? The only one I can find is spec'ed for 5V, and absolute max specs for output current are not included on that datasheet.

rogs
07-30-2013, 09:28 AM
Rogs, can you link to the HT9170 datasheet that has output drive specs for vcc=3.3v? The only one I can find is spec'ed for 5V, and absolute max specs for output current are not included on that datasheet.

This official Holtek data sheet is the only one I've found

http://www.holtek.com/pdf/comm/9170v111.pdf

and doesn't specifically describe a 3V supply output rating separately.

Indeed, the only parameter which appears to have a separate 3V characteristic listed is the input signal level.
That's understandable.... as we've discussed earlier, you really don't want the audio input signal to clip!

The tristate output characteristics seem to be specified with regard to the effective output driver 'on' resistance, and the internal gate source 'on' voltage. That explains the difference between the sink and source capabiblites.

The relatively low current output capabilities suggest a fairly high 'on' resistance. That also explains why they don't quote a max rating. Try and draw more current, and the device either starts to turn itself 'off' (source limit) or the output voltage rises (sink limit). Neither, presumably causing any harm to the device?...

I was trying to keep the description simple, by just suggesting trying to draw less from these puny outputs.
Probably a mistake on my part. If you want to drive LEDs with any significant current - use an output buffer!

One further point.... I can see how your recommended circuit will hold the output pins 'low' for a few seconds (although as we have discussed, the condition after that would remain undetermined), but I can't see how it will stop pin 15 LED from 'pulsing' on during power up?
Pin 15 is not a tristate output, like the 4 outputs on pins 11-14?

I've never had a problem myself with pin 15 output 'pulsing' on power up -- only with the unknown latched states of pins 11-14.

I've also never tried to use this device with a 3.3V supply. From my comments above, I suspect the output source current capability will be even worse (the gate source voltage will tend to turn the output off at a lower current limit). But how much worse?.......
The sink capabilities should remain the same, I would imagine..

With a 3.3V supply, it's probably going to need an output drive buffer to light LEDS effectively.......

Ron H
07-30-2013, 02:55 PM
This official Holtek data sheet is the only one I've found

http://www.holtek.com/pdf/comm/9170v111.pdf

and doesn't specifically describe a 3V supply output rating separately.

Indeed, the only parameter which appears to have a separate 3V characteristic listed is the input signal level.
That's understandable.... as we've discussed earlier, you really don't want the audio input signal to clip!

The tristate output characteristics seem to be specified with regard to the effective output driver 'on' resistance, and the internal gate source 'on' voltage. That explains the difference between the sink and source capabiblites.

The relatively low current output capabilities suggest a fairly high 'on' resistance. That also explains why they don't quote a max rating. Try and draw more current, and the device either starts to turn itself 'off' (source limit) or the output voltage rises (sink limit). Neither, presumably causing any harm to the device?...

I was trying to keep the description simple, by just suggesting trying to draw less from these puny outputs.
Probably a mistake on my part. If you want to drive LEDs with any significant current - use an output buffer!

One further point.... I can see how your recommended circuit will hold the output pins 'low' for a few seconds (although as we have discussed, the condition after that would remain undetermined), but I can't see how it will stop pin 15 LED from 'pulsing' on during power up?
Pin 15 is not a tristate output, like the 4 outputs on pins 11-14?

I've never had a problem myself with pin 15 output 'pulsing' on power up -- only with the unknown latched states of pins 11-14.

I've also never tried to use this device with a 3.3V supply. From my comments above, I suspect the output source current capability will be even worse (the gate source voltage will tend to turn the output off at a lower current limit). But how much worse?.......
The sink capabilities should remain the same, I would imagine..

With a 3.3V supply, it's probably going to need an output drive buffer to light LEDS effectively.......My circuit does not hold the outputs low. The outputs are still free to go high or low. On power up, the MOSFET will be off for a second or so, which interrupts the current flow between the LEDs and ground. When the gate voltage gets high enough for the MOSFET to turn on, any outputs which are still high will turn on their respective LEDs.
Pin 15 is not tristate (according to the datasheet).
As I see it, if pin 15 does flash on power up,your circuit will force OE to be high immediately, allowing the DATA LEDs to flash if their respective outputs are high. And it won't prevent pin 15 from flashing, either. I realize that your circuit assumes that pin 15 will not come up high on power up, but that's the problem our OP is trying to solve.
CMOS source AND sink currents suffer as vcc goes down. I suspect that you could drive LEDs with no current limiting resistor, if you didn't need the logic outputs as inputs to another circuit, but I would probably still put in a low-value series resistor. As you said, buffers are required if you want significant light from the LEDs.

rogs
07-30-2013, 03:23 PM
My circuit does not hold the outputs low. The outputs are still free to go high or low. On power up, the MOSFET will be off for a second or so, which interrupts the current flow between the LEDs and ground.
Sorry Ron, I had misread your circuit. I had thought you had connected your 'on delay' circuit to pin 10, not the LED common. My mistake, sorry.
I can now see that you have disabled the LED common line, so as you say, all LEDS should power up off.. although any the output ones may still come on after the 2N7000 gate time constant has charged, without also including a power on reset bistable, along the lines of the one I'm suggesting.

As I say, I have not seen pin 15 pulse 'hi' on power up, but if it does then increasing the time constant on my bistable circuit (if necessary) should allow pin 15 to 'settle' lo before the bistable is 'reset'. It would then require a valid code to 'set' the bistable and set pin 10 hi, to enable the outputs.

Ron H
07-30-2013, 04:41 PM
As I say, I have not seen pin 15 pulse 'hi' on power up, but if it does then increasing the time constant on my bistable circuit (if necessary) should allow pin 15 to 'settle' lo before the bistable is 'reset'. It would then require a valid code to 'set' the bistable and set pin 10 hi, to enable the outputs.If pin 15 does pulse high on power up, it will drive OE high, irrespective of the time constant on the bistable reset pin. Only when pin 15 goes low on its own will the reset on the bistable have any effect.
If the pin 15 pulse is shorter than the reset time due to the RC, then OE will just be a copy of the pulse on pin 15.

Etronic
07-30-2013, 05:13 PM
I been having trouble with the outputs coming on to light up
with the 3.3V.So i increased my input voltage to 5.0V and works
much better for the LEDs.But that does not to say it didn't work it did.
but the leds are low.And i used a 200hm resistor.

Can i still use 1K resistor for the LEDs with a 5.0V power supply input.
Or will i need to use a resistor higher then 1k.As rogs suggested.


Also im more confused to which of the power on reset circuit to use.
after reading both of your post.Help!:confused:

Ron H
07-30-2013, 05:24 PM
I been having trouble with the outputs coming on to light up
with the 3.3V.So i increased my input voltage to 5.0V and works
much better for the LEDs.But that does not to say it didn't work it did.
but the leds are low.And i used a 200hm resistor.

Can i still use 1K resistor for the LEDs with a 5.0V power supply input.
Or will i need to use a resistor higher then 1k.As rogs suggested.


Also im more confused to which of the power on reset circuit to use.
after reading both of your post.Help!:confused:If they are bright enough with 1k, use that. If not, try 470Ω. You could have brighter LEDs with a hex buffer of some sort.
My opinion is that rogs' circuit will not prevent pin 15 from flashing the LED on power up, as I explained in my last post. If rogs can explain how I am wrong, I will humbly back down.:)

Etronic
07-30-2013, 09:43 PM
Hi Ron

Then i will use your added circuit Ron H.And i have most of those parts.And i don't want to add more
parts then i need to.Do to current draw from battery and size of the circuit.:)

rogs
07-30-2013, 11:48 PM
If pin 15 does pulse high on power up, it will drive OE high, irrespective of the time constant on the bistable reset pin. Only when pin 15 goes low on its own will the reset on the bistable have any effect.
If the pin 15 pulse is shorter than the reset time due to the RC, then OE will just be a copy of the pulse on pin 15.


As I mentioned before, I personally have never seen pin 15 go 'hi' during power up, although I concede it may do for a fraction of a second during the application of power to the system.....
If that is a problem, you can eliminate even the momentary 'hi' status of OE on power up, by connecting point 'c' in your drawing to one input of U3.
So, one input of U3 would go to pin 15, and one input to point 'c'.

OE would then never goes 'hi' until receipt of a valid DTMF code, and the output latches are maintained in a known (HI-Z) state until that first code is received.

I just can't see how using your 2N7000 'LED common' circuit to delay the LEDs coming on defines the output latch condition, once the gate time constant has charged?.....

Ron H
07-31-2013, 05:23 AM
As I mentioned before, I personally have never seen pin 15 go 'hi' during power up, although I concede it may do for a fraction of a second during the application of power to the system.....
If that is a problem, you can eliminate even the momentary 'hi' status of OE on power up, by connecting point 'c' in your drawing to one input of U3.
So, one input of U3 would go to pin 15, and one input to point 'c'.

OE would then never goes 'hi' until receipt of a valid DTMF code, and the output latches are maintained in a known (HI-Z) state until that first code is received.

I just can't see how using your 2N7000 'LED common' circuit to delay the LEDs coming on defines the output latch condition, once the gate time constant has charged?.....I thought we had already agreed that the data outputs may still come up in any state, and that 1 or more of the data LEDs may be on after the MOSFET turns on.
My circuit was to address the problem of DV flashing on turn on. I added the other LEDs to the circuit because it was a free "feature". :)
Rogs' circuit avoids having the data LEDs come up randomly on power up, but does not address the issue of DV flashing on power up.
I think the attached circuit will address both issues.

EDIT: Rogs, I couldn't figure out what circuit this refers to: you can eliminate even the momentary 'hi' status of OE on power up, by connecting point 'c' in your drawing to one input of U3.
So, one input of U3 would go to pin 15, and one input to point 'c'.
Maybe that solution is simpler than mine.

rogs
07-31-2013, 08:37 AM
I thought we had already agreed that the data outputs may still come up in any state, and that 1 or more of the data LEDs may be on after the MOSFET turns on.
My circuit was to address the problem of DV flashing on turn on. I added the other LEDs to the circuit because it was a free "feature". :)
Rogs' circuit avoids having the data LEDs come up randomly on power up, but does not address the issue of DV flashing on power up.
I think the attached circuit will address both issues.

EDIT: Rogs, I couldn't figure out what circuit this refers to: Maybe that solution is simpler than mine.

I have to admit, I thought the problem with the data output LEDs randomly coming on and staying on was a more serious issue than a possible 'momentary' flash of the DV output?..... but your latest circuit will deal with both issues! :)

Ron H
07-31-2013, 01:51 PM
I have to admit, I thought the problem with the data output LEDs randomly coming on and staying on was a more serious issue than a possible 'momentary' flash of the DV output?..... but your latest circuit will deal with both issues! :)I agree.
Maybe Etronic can explain why DV flashing on power up is so annoying.

Etronic
08-01-2013, 12:43 AM
ron

The DV LED flashing on power-up is not really that annoying.
I just don't want any false readings of any invalid tones coming on.
Before and after any audio sound is pick up from the amp.To the decoder.

rogs
08-01-2013, 03:58 PM
I just don't want any false readings of any invalid tones coming on.


DV (pin15) won't go high unless and until the decoder receives a 'valid' tone pair.
How long the tone pair needs to be valid before allowing pin 15 to go high, and indicate the updating of the output latches, will depend on the values of the pin16/pin17 time constant components....

Invalid tone pairs, third tone, dial tone and noise rejection are all pretty good with the HT9170.

The data sheet details the figures...

Etronic
08-10-2013, 12:57 AM
Update!

Enclosed circuit.

Its working.per-say but? theres a gitch in the circuit when the ouput tones come on.
Im using an online Dtmf tone Generator.
The audio amp is working fine.Tested the audio output.Theres a signal on the ouptput of the audio amp.So i know it is giving a valid signal ouput.

Example:
sWhen i press any key on this online key pad say #1 the DV led light up and led 1 lights up.Then i press key #2 and led DV lights up.
Now when i press #1 again it dose not light up.And this happens radomly
with each key i prees.Meaning sometimes they working and sometimes
the key i press are not working and i get no output and that number dose not light up.

What wrong any ideas. Help!:confused:

Ron H
08-10-2013, 03:32 AM
Are you sending the tone generator audio through the microphone and the audio amp? If so, post the schematic.

Etronic
08-10-2013, 09:14 AM
Are you sending the tone generator audio through the microphone and the audio amp?

Yes! The microphone picks-up the audio.Even at 1'' to 12'' away.

And theres a signal output from the amp.

Just don't understand what the gitch could be with the decoder.:confused:
As stated it my last post.

rogs
08-10-2013, 01:14 PM
Example:
sWhen i press any key on this online key pad say #1 the DV led light up and led 1 lights up.Then i press key #2 and led DV lights up.
Now when i press #1 again it dose not light up.And this happens radomly
with each key i prees.
What wrong any ideas. Help!:confused:

When you press key#1 again, does the DV led light up, even if the key#1 led doesn't?.....

If not, then the decoder is not seeing a valid code pair... or at least not for long enough continuously to update the latch.

You could reduce the value of the resistor connected to pin #16 to 100k, see if that helps......

If the microphone preamp is 'clipping' (because the input signal level is too high) then that may be seen as an invalid state.

When you press a new key that does not update the latch as you expect, I assume the existing 'state' is maintained? ....

Etronic
08-10-2013, 07:27 PM
When you press key#1 again, does the DV led light up, even if the key#1 led doesn't?.....

Yes! Sometimes that will happen.I also put a new LED for LED #1 to make
sure the LED works.



If not, then the decoder is not seeing a valid code pair... or at least not for long enough continuously to update the latch.


This also happens radomly.

If the microphone preamp is 'clipping' (because the input signal level is too high) then that may be seen as an invalid state.


How do i stop the amp from clipping if that is one of the problems.
How do i keep the signal level going to high.If thats preventable.






Thats correct! Help!:eek: What should i do?

Ron H
08-10-2013, 11:26 PM
[COLOR=blue]How do i stop the amp from clipping if that is one of the problems.Turn down the gain using the pot. You were originally thinking you needed AGC. If your signal source is not fixed relative to the mic, or is not nearly constant amplitude, you might need AGC.

rogs
08-11-2013, 12:42 AM
As Ron suggests, reduce the gain. The HT9170 will accept signals with a 30dB amplitude range as valid, so you probably shouldn't need AGC, if you've selected a useful gain range. Indeed , if an AGC circuit 'hunts down', it may pick up more room noise, which can cause problems.

You might be surprised just how little signal the device will accept as valid.

What it won't accept as valid are signals that are too large in amplitude, and which clip the analogue input before it is processed within the decoder.

One further thing that may be casuing a problem. The decoder is looking for a 'valid' tone pair. Not only will that need to be within the amplitude range described above, but it will need to be free from any other spurious noise introduced into the signal path. If the room acoustic is noisy, the device will not be able to 'hear' the tone pair accurately, and can reject the tone pair as invalid.

So to start with, reduce the gain,and make sure the 'room' is quiet!

Etronic
08-11-2013, 11:35 PM
This is really strange i got the circuit working at 2.5ft with the volume at its highest level away from my computer.Then it stop outputing some of the tone as i pushed any key on the online dmtf generator.And the gain on the audio amp was a gain of 20,and a gain of 10 on the decoder.In my
first in this thread that i want to be 10ft away.How could i do this with out an AGC in the circuit.

So Now I.
Reduced the audio's gain.The resistance on the Pot is now 14K instead of the 19K i had. I also put in another new LED on the DV pin.

I also changed the steering resistor from 300K to 100K as rogs suggested.
This change didn't make to much of a difference.So put back the 300K resistor back in.

And the room is very quiet!

What else could i do?

rogs
08-12-2013, 09:10 AM
The next step is to confirm whether the unreliabiblity problem is with your 'online generated' DTMF source, or the microphone audio path.

Disconnect the audio amplifier, and connect your DTMF source output directly to the 1uf capacitor point that was the audio amplifier output point. Reduce the signal gain if necessary, and confirm that the system works reliably.
If it does, the problem is in the audio path. If not, then the problem is with the DTMF source generator.....

Etronic
08-13-2013, 11:08 AM
Disconnect the audio amplifier, and connect your DTMF source output directly to the 1uf capacitor point that was the audio amplifier output point. Reduce the signal gain if necessary, and confirm that the system works reliably.
If it does, the problem is in the audio path. If not, then the problem is with the DTMF source generator

I've disconnected the audio amp from the circuit.And i connected the dtmf source generators output directly to the input of the decoder and the decoders output tones worked perfectly.
Each time a key is press the DV pin lights up and the decoders tone LEDs light up for each key that was pressed. Now we know its not the decoder.

I also tested the audio amps output for a signal.Thats good too.

So! further testing.
I connected the two circuits back up.And adjusted the gain on the audio amp from a gain of 9 to a gain of 20.What i found was the distance from
the dtmf source generator to the computer vs gain makes a big difference
in whether you get a signal for the audio amp to amplify that signal for the decoder to process it and for the DV to light up and to output a tone from the decoder.
Also the microphone has alot to do with picking up the signal before its
amplified.

First i set the audio gain to 9 then moved the mic at different distances
so at 1'' away form the computer i get perfect output tones.All LEDs
lit up when each key that was pressed.At 2'' only some lit up. Like keys 9,8,A,B,C,0.. Any thing pass the 2'' distance none of the LEDs lit up.
Then i increased the gain as i got farther away from the computer.
vs the distance from the microphone and found that at a gain of 12 to
20 i got a max distance of 6'' and all outputs tones worked perfectly.
Anything beyond the 6'' at a gain of 20...No lights will light up and no output tones on the decoder.

So i'm thinking i will need a much better low noise higher gain microphone for longer distances.Increase audio gain on amp But? could increase the noise factor of the amp.And also maybe increasing the gain on the decoder. Or a AGC low noise low current audio amp with high bandwith.

If this is the problem and increase the distance to 10ft. Any thoughts on this.

rogs
08-13-2013, 08:26 PM
It would be useful to hear a recording of the output of your mic and audio amplifier.. preferably a recording of your DTMF generator.
Then at least we might get an idea whether the problem is with noise, distortion or extraneous noise pick up.
You can find a short sample of the sort of thing you should be hearing here:
www.jp137.com/las/DTMF.mp3

(I would upload as an attachment, but for some reason I can't seem to upload an mp3 as an attachment????:confused: .. and it's only a small file! (about 150K)...

Anyway, this is a recording of DTMF from the 'handsfree' speaker output of my study phone, made at a distance of just over 10 feet.
It is using a cheap WM61A Panasonic electret mic capsule, and is recorded into my portable Olympus audio recorder. That recording should decode accurately.
If your audio amp sounds like that, I can't see why you have problems decoding accurately....even at a distance of 10 feet......

rogs
08-13-2013, 11:57 PM
I don't have a portable Olympus audio recorder to record too.
those recoders have filtering and dps in them to help the sound
come in clearer.I think thats way you recorded that dtmf tone sound
over ten feet.


No -- no filters or 'DSP' added to the recording. Just the internal mic preamp in the recorder, and the cheap electret mic capsule I mentioned. Recorded as linear PCM, to show a 'typical' audio ampifier response in a reasonably quiet room at 10 feet.

I have no idea what op-amp you are using? There is no reference number on your schematic.

There is no 'magic' about what I recorded. If you use a reasonable quality electret capsule (like the Panasonic WM61A I used --very cheap) and a reasonable audio preamplifier, you will get similar results.
You have to understand that analogue audio electronics is not the 'yes' and 'no' world of digital electronics. You still have to experiment to get the best results.
Without an oscilloscope -- or, at the very least, the ability to 'listen' to the output of your amplifier, you will have no idea where the reason for your false decoding lies....
A good way is to record the output........

rogs
08-14-2013, 08:05 AM
Where did you get yours.WM61A Panasonic electret mic capsule.
It looks like digikey don't stock them anymore.

Maybe i got a defected Mic.And its working but not correctly if that makes
any sense.

I'm in the UK, so I got mine from here:

http://www.felmicamps.co.uk/products/felconnectorsand.html


so that doesn't help you much I'm afraid...

I believe the WM61A is going obselete, so although it's simple enough to find them on ebay, you can't be sure they're not fakes... especially if the price starts to rise because of rarity.

It was just a suggestion.... most cheap electrets should be able to produce similar results.

As I say, you need to listen (and/or record) the output from your audio amp to get a real idea of what's happening. It doesn't have to be DTMF at this stage... even speech or music will do.....just plug the output from your audio amplifier into the 'line in' on your computer sound card (not 'mic in'), and record onto that....

Etronic
08-14-2013, 11:20 AM
As I say, you need to listen (and/or record) the output from your audio amp to get a real idea of what's happening. It doesn't have to be DTMF at this stage... even speech or music will do.....just plug the output from your audio amplifier into the 'line in' on your computer sound card (not 'mic in'), and record onto that....


What will this tell me about the amp. Say for instants the music i record.
If it sound OK...What will that tell me.

Also? What audio amp circuit did you use.To pick up the sound with.
Do you have a schematic for the amp.

Did you look at my amp.Is there anything out of the norm that i need to change.Or what needs to be added or removed to fix it.if you think that is the problem.

rogs
08-14-2013, 09:21 PM
What will this tell me about the amp. Say for instants the music i record.
If it sound OK...What will that tell me.

Also? What audio amp circuit did you use.To pick up the sound with.
Do you have a schematic for the amp.

Did you look at my amp.Is there anything out of the norm that i need to change.Or what needs to be added or removed to fix it.if you think that is the problem.


What it will tell you about your amp is whether there is any noise or hum being picked up via the supply rails, and distorting the output.

I haven't used an amplifer in a non inverting mode that you have chosen. I tend to use the inverting mode for this type of unit. Your circuit has a very high input impedance (not really necessary for an an electret mic) and the half rail supply to the non inverting input is not decoupled. Neither is the DC feed to the microphone.

It may work OK......listening to an actual recording would tell you a lot more. If there is any hum or distortion you will hear it.

I didn't use any amplifier other than the mic preamp within my Olympus recorder. I just connected the electret mic to the recorder.

If you connect the output of your sound card and replay my recording directly to the input of your decoder, and it decodes OK then you know that it can be made to work at a distance of 10 feet.. because that's how far away that recording was made.

I've attached a quick sketch of how I would have started out my experiments for a project like this. Not saying it will work OK first time, but it should keep out any hum or noise that might be introduced into the input via the DC supply.
It's just a suggestion. I've not built it.
As I say, you can tell a lot more about audio amplifiers by listening to them, rather than relying on the circuit diagram as just being 'right'.
As I said before, analogue audio is not like digital electronics... it's not just 'on/off ' or '1 or 0'. There are lots of 'shades of grey' in between, and they need to be tried out with practical circuits.....

Etronic
08-16-2013, 02:13 AM
If you connect the output of your sound card and replay my recording directly to the input of your decoder, and it decodes OK then you know that it can be made to work at a distance of 10 feet.. because that's how far away that recording was made.


I took a mono plug with wire on other end.Pluged THE PLUG into the output of ear phone on my computer. AND took the wire side and connected that to the 1uF cap thats connected to my decoder on pin 2.And then replay back your DTMF recording.The DV LED did not lightup nor did any of the output LEDs light up. So It didn't work.

I then played the DTMF app that i used online.Each key that i pressed
the DV LED lit up and the LEDs corresponded to that key lit up. So i know the decoder is working alright.

For some reason your DTMF recording that was recorded at 10ft,Just didn't work. I'm :confused:

NEXT! I'm GOING to add the parts to my audio circuit to what you
have in your schematic and see what happens when connected to the decoder.
Should i use the LVM796 audio amp with the parts added in your schematic.
With an inverting set up. THIS might not work.
>Look at all Audio gurus POSTS ABOUT USING AN INVERTING SET-UP IN THIS THREAD.
with this audio amp.This is way i chose this part for the high impedance.In a non-inverting set up.

I just don't want to go backwards and have to start all over again with a different audio amp.

Also what are these values that i circled in RED In your schematic.Are they, 2.2k, 2.2k,10uF,1uF,and .1uF

rogs
08-16-2013, 11:15 AM
Yes - those are the values in the red circled items.

I have chosen the input resistor value as 2.2k to match the effective output impedance of (now) decoupled microphone feed resistor. You could make that value higher -- it is often recommended that the input impedance of the preamp needs to be higher.. although other commentators suggest matching the impedances offers the best results.
If you do go higher, then your pot value will need to be higher too, to maintain the gain.
With an input resistor of say 10k you would need the pot to then be 200k, to get your maximum gain of 20.

With your non-inverting circuit you set the input impedance at 50k (the two 100k resistors connected to your non inverting input are seen in parallel from an AC (signal) point of view).
The disadvantage of that configuration is that any noise or hum on the supply rails will be subject to the full gain of the pre-amp. Hence my suggestion to record the output from your amplifier, so that you could check.

I think maybe I should now stand back a little and let someone else offer you some suggestions...I don't want you to feel you are going 'backwards'!
I just thought I'd suggest one or two ideas that I've used myself ( and which worked for me!) but I do understand that you may not believe me.
After all, this is the internet, and you have no idea whether I know what I am doing or not! :)

Maybe time for someone else to pitch in with some suggestions, perhaps?....

Etronic
08-16-2013, 01:59 PM
Yes - those are the values in the red circled items.

I think maybe I should now stand back and let someone else offer you some suggestions...I don't want you to feel you are going 'backwards'!
I just thought I'd suggest one or two ideas that I've used myself ( and which worked for me!) but I do understand that you may not believe me.
After all, this is the internet, and you have no idea whether I know what I am doing or not! :)

Time for someone else to pitch in with ideas, I think.....

I didn't mean you were giving me wrong advice.Your help is very appreciated.And i didn't mean you were taking me 'backwards'
Not in the lease.
I ment since i got a amp that seems to be working.
I just don't want to incorporate another amp to find its not going
to work in the circuit.From some one else who might post to this thread.
And start all over again.

You and Ron H are the only ones who been there to help me out on this circuit. And i appreciated you taking your time in helping me with this project.If you didn't.I don't think i would have gotten to where iam now with this project.
I think to many more suggestions from other posters will confuse the
situation further.And no one else has posted.

I just want to know the amp in your schematic is still the amp i have
in my circuit.LMV796.

I would appreciate if you would still help on this.

rogs
08-16-2013, 08:13 PM
I just want to know the amp in your schematic is still the amp i have
in my circuit.LMV796.


I didn't have any specific opamp in mind when I sketched out the circuit - and as I mentioned earlier in the thread, I've not used the device you are using. But it should work OK.

I did make sure that I could decode my 'recorded' file, using a software DTMF decoder (I don't have access to a HT9170), and it did work OK.
But I did notice it was a bit more fussy about the threshold range it would work over.
Your online DTMF encoder was more tolerant. ( I tried to find the link to that encoder you made in one of your earlier posts, but some of those seem to have disappeared?:confused: )...

Anyway, that is perhaps to be expected...software DTMF decoders (especially freeware ones!) do not have the sophisicated band splitting and clipping algorithms that the hardware decoder has. But it does show that you are likely to find some difference between decoding 'pristine' DTMF, and that recorded over a distance.

Once you are satisfied that the preamp is producing reasonable amplified 'copies' of your generated code, I should try and find a range of input levels that will work reliably with the source and microphone at fairly close range. Then slowly increase the distance, and the gain of the preamp, to see whether you can maintain a reliable decode at further distances.
You should expect to increase the gain by 2 (6dB) for every time you double the distance.

At some distance the corruption of the recorded signal -- by amplifer noise, room acoustics etc -- will make the reception unreliable. Only by experimenting will you discover where those limits are.

If it turns out that it's no where near as far as you'd hoped, then you can look at AGC to help. But that will bring a whole new can of worms to the project, so one thing at a time!

Without access to an oscilloscope, you really are going to find 'fault finding' your audio circuits a bit difficult. As I've said before, the next best option is to listen to your amplifer output.... connect it to your sound card input and use headphones. You'll soon hear whether your DTMF 'sounds' as it should. If you can't hear it sounding 'clean', neither can your decoder!

The audio side of this is not an ideal starting project.... it really is going to need methodical testing, to discover exactly where you are with the whole signal path....

Etronic
08-17-2013, 04:08 AM
rogs

I tryed your schematic sketch you posted in post #91.
Unfortunately it did not work with the LMV796 amp.In
the inverting setup.

So! I disconnected the circuit and connected the way i
had it.It worked perfectly then at the 6'' distance.
At 2.5ft it works But not all keys pressed from the online DTMF lit up.
The ones that did light up are A,B,C,D,8,9,.,#.. 1,3,4,5,6,7,0 did not.
Maybe the other lower FQ tones are being cutoff do to a low cc1 cap
and cc2 cap.Thats why at a shorter distance they pickup. but? cutoff the FQ at a longer distance.And the gain needs to increase as you pickup these low and higher FQ tones further away.Does this make any sence.
Also im thinging these FQs need to Be pick-up at Between 100hz
to 10,000hz. low and high frequencies.Just suggesting.

I was reading the LMV796 works better at shorter distances.
Maybe you can look at the Datasheet.Enclosed.



Once you are satisfied that the preamp is producing reasonable amplified 'copies' of your generated code, I should try and find a range of input levels that will work reliably with the source and microphone at fairly close range. Then slowly increase the distance, and the gain of the preamp, to see whether you can maintain a reliable decode at further distances.
You should expect to increase the gain by 2 (6dB) for every time you double the distance.

At some distance the corruption of the recorded signal -- by amplifer noise, room acoustics etc -- will make the reception unreliable. Only by experimenting will you discover where those limits are.

If it turns out that it's no where near as far as you'd hoped, then you can look at AGC to help. But that will bring a whole new can of worms to the project, so one thing at a time!


The best i got is 6'' Max with this Audio 0p amp
And all tones worked perfectly.So it dose work!

It did work at the 2.5ft range.But? like i said.Only certain keys
lit up. With the DTMF online encoder.


Link to the online encoder.
http://www.cs.washington.edu/education/courses/cse100/04au/misc/tones/dtmf.html

rogs
08-17-2013, 07:55 AM
Sorry to read that the inverting version did not work. As you will see from fig 49 and fig 50 of the data sheet (page 16) both versions are suggested.

I cannot believe that any bandwidth limitations will distinguish between the upper and lower tone groups. Plus the fact that the 'twist' (different levels) permitted between the two tone groups is quite substantial.

I think you need to record the output of your amplifier -- at a working, part working and non working range -- and post those sample recordings, so that maybe we can understand better where the problem is.
I can't think of any further to suggest, without hearing a sample.

Etronic
08-17-2013, 07:52 PM
Sorry to read that the inverting version did not work. As you will see from fig 49 and fig 50 of the data sheet (page 16) both versions are suggested

No! I didn't use the inverting circuit fig49-50 on page 16 in the datasheet.

I used your sketched schematic inverting circuit you posted #91 as you drew it.And with the parts you used. That schematic 'did not work'.

I haven't build the inverting circuit in the datasheet.With there parts.

rogs
08-17-2013, 09:24 PM
I used your sketched schematic inverting circuit you posted #91 as you drew it.And with the parts you used. That schematic 'did not work'.


As I mentioned before, it was only a suggestion to try. That schematic does work... but not necessarily using that opamp and that supply voltage, and using an unknown electret capsule...

As I mentioned before, I little or no experience with low voltage preamps -especially mic preamps - so to some extent you are a bit of a pioneer in that area.
All I can do is make suggestions.

For example, for this kind of project I would probably have started use a transistor front end, with a TLO71 opamp following stage, and utiltising a 12 or 24 volt DC supply. I would also choose a known mic capsule, with a low noise internal preamp.

But you don't have those options, so you're making the best of the options you do have.

From what has happened so far, it would seem as if you might be best carrying on with your non inverting amplifier.

Post a recording on what you've achieved so far, so that we can get some idea of the results you're actually getting....

Etronic
09-02-2013, 09:30 AM
rogs

Im going to try the circuit you suggested in post #15 where you stated
keep it simple by using the LM358 circuit.And subsituting it with the
LMV358 part.R3 and R4 would need to stay in the circuit
to bias the IC with a single power supply as stated in the datesheet.
But you suggest removing them. Why? The circuit my not function
correctly with out those resistors in the circuit.

http://howcircuits.com/lm358-preamp.html

If this circuit dose not give me the results i need. Maybe you got a completed circuit schematic that you
used and build for a Preamp.With these parts.

rogs
09-03-2013, 12:56 AM
rogs

Im going to try the circuit you suggested in post #15 where you stated
keep it simple by using the LM358 circuit.And subsituting it with the
LMV358 part.R3 and R4 would need to stay in the circuit
to bias the IC with a single power supply as stated in the datesheet.
But you suggest removing them. Why? The circuit my not function
correctly with out those resistors in the circuit.

http://howcircuits.com/lm358-preamp.html

If this circuit dose not give me the results i need. Maybe you got a completed circuit schematic that you
used and build for a Preamp.With these parts.

In post #15 I suggest removing R3 and R4 and then connect pin 3 directly to pin 1 (and/or) 4 of the HT9170 (as I have in my circuit sketch in post #92). This will let you use the internal 'half rail' voltage reference (2.5V) within the HT9170 to provide the bias for your opamp, rather than the resistors.
This is a much lower impedance reference than the resistors provide, and should help with any noise or hum problems that may come form either the supply rail itself, or from the high value of the resistors R3 and R4.
Not saying that will occur, but it may

As I mention in several of my previous posts, a recording of the DTMF you have manged to pick up so far would give a much better idea of what's actually happening, and hopefully give some pointers as to why you're not getting the results you need.....

Etronic
09-21-2013, 12:56 AM
I could not record any of the LMV796 audio's output.To check its output for any noise,hum,distortion,hissing,etc, etc.My computer will not record this data.Reason. I just don't know.


This is in reference to the LMV796 op amp that i used in my circuit.The non-inverting circuit. In the datasheet

As stated in post #93
With your non-inverting circuit you set the input impedance at 50k (the two 100k resistors connected to your non inverting input are seen in parallel from an AC (signal) point of view).
The disadvantage of that configuration is that any noise or hum on the supply rails will be subject to the full gain of the pre-amp. Hence my suggestion to record the output from your amplifier, so that you could check.


Couldn't record audio.:mad:

So lets say there is that noise and hum or distortion on the
supply rails and going into the input and coming out of the output what can i do to remedy these characteristics in the LMV796 circuit.May there is a problem with a combination of these characteristics.And thats why
i get DTMF pick-up at a maximum of only 6''.And not the 10ft i want.


Also in post #91 you made a sketch of a inverting set up circuit with
no bias resistors.
I was going to try that with LMV358.Would an inverting setup
work better then in a non-inverting set up.As in your sketch.

rogs
09-21-2013, 08:26 PM
Also in post #91 you made a sketch of a inverting set up circuit with
no bias resistors.
I was going to try that with LMV358.Would an inverting setup
work better then in a non-inverting set up.As in your sketch.

Both options should work OK. The idea of not using the bias resistors was to eliminate the possibility of high impedance hum pick up, when using 100k bias resistors, or the possibility of noise pick up from the supply rail, which is then amplifed by the preamp.

It is possible that neither of these things are happening, and that your problem is elsewhere. Which is why I keep suggesting that you record the output from your existing circuit..... Without access to an oscilloscope, listening to an audio output is the next best thing to give clues on what's wrong.....
If you can't record at the moment, I would suggest that your next best step is probably to fix the computer recording problem....

Etronic
10-04-2013, 08:59 PM
Has any one ''else'' on here ever build an audio amp using the LMV796.

I been try to get a distance of 10ft.But having no luck with that.

The most i could get is 6'' away form my computer using an online DTMF
generator. Could it be clipping on the output or something like internal
noise.

Would any one on here who knows about audio and use op amps
willing to help if i send them a Sample of the LMV796 AMP.
To see way its not picking up dtmf tone ten feet from there computer.
Maybe an ''engineer'' on here would be willing to test this amp out for me.
i could send you an sample.the circuit im use is the non-inverting setup
on page 16 in the datasheet.

http://www.ti.com/lit/ds/symlink/lmv796.pdf

It dose work. But i'm only getting 6'' picking up the dtmf tones generated from
my computer.Maybe it needs a AGC circuit.

Ron .H

Would you be willing to have a go at this amp if i send you a sample.

ronv
10-04-2013, 11:09 PM
I have no experience with this, but I think the minimum input is 27mv. Since you are using the inverting input for the preamp you lose about 1/2 the gain. So maybe a gain of 5. Another 10 in the chip so maybe 50 total. maybe a mv out of the mic at a couple of inches leaves it short. Maybe try a 200k pot on the preamp. It may never work very good at 10 feet - a lot of bounces.

Etronic
10-05-2013, 04:26 PM
I have no experience with this, but I think the minimum input is 27mv. Since you are using the inverting input for the preamp you lose about 1/2 the gain. So maybe a gain of 5. Another 10 in the chip so maybe 50 total. maybe a mv out of the mic at a couple of inches leaves it short. Maybe try a 200k pot on the preamp. It may never work very good at 10 feet - a lot of bounces.

Hi ronv

I'm ''not'' using the inverting input. I'm using the ''non-inverting'' input.
on page 16 in the datasheet. Figure 50.I have the mic connected to the non-inverting input.For a gain of 20. At 6'' away max i get.

What do mean by,alot of bounces.Please explain!

Which op amp would you use to get the 10ft distance.
Must be low noise,low current for battery use and high gain.
Also high slew rate and the supply voltage must be 2.7V-5.0V INPUT.

My circuit im using is from figure 50.
Why can't this circuit im using work at 10ft.

bertus
10-05-2013, 04:58 PM
Hello,

What type of mic are you using?
You can decouple the mic from the main power by a resistor and a capacitor.
I have drawn them in your schematic:

http://forum.allaboutcircuits.com/attachment.php?attachmentid=60005&stc=1&d=1380992247

This will prevent noise from the powersupply to enter the preamp.

Bertus

ronv
10-06-2013, 03:36 AM
Lots of schematics..:) He says as he adds one more. But you have the non-inverting one. Good.

Here is a simulation with a 60 dba spl. That's about like being in your living room listening to the TV. Maybe your tone is louder or quieter. I don't know. Anyway at that level you need more gain. So I took the bertus schematic with the filter and gained it up to where there is about 50 mv to the 9170.(see pot & resistor changes) Speaking of that what are pins 1 and 4 of the 9170 tied to now that you have the non inverting setup? :rolleyes:
Your op amp is ok - maybe a little fast for a breadboard so I added a 100pf cap across it so maybe it won't oscillate.
By bounces I mean echos in the room from walls and furniture and stuff.
You have a 5.5 volt battery?

Etronic
10-08-2013, 06:59 PM
Hello,

What type of mic are you using?
You can decouple the mic from the main power by a resistor and a capacitor.
I have drawn them in your schematic:




I'm using a electret mic capsule from digikey P9925-ND. But its it been replaced with another mic don't know the part number.

bertus
10-08-2013, 07:08 PM
Hello,

The following project from ESP might be an interested read for you:
http://sound.westhost.com/project93.htm

There is told how to use an electret microphone in combination with a preamp.

Bertus

Etronic
10-08-2013, 07:28 PM
ronv

So I took the bertus schematic with the filter and gained it up to where there is about 50 mv to the 9170.(see pot & resistor changes) Speaking of that what are pins 1 and 4 of the 9170 tied to now that you have the non inverting setup? :rolleyes:


Pin1 and Pin 4 are connected together.As in the datasheet of the 9170.
I connected the output of the lmv796 to pin 2 of the 9170 from the 1uF capacitor on the output.The 10K and 100k sets the gain of 10 on the 9170.

How would you connect the amp to the 9170.

I have 4 x1.5V cells for my battery which is 6V. But its been use in other circuits so its drain down some.
Thats why i get 5.5V-5.6V. No! there is no battery at 5.5V.

Etronic
10-13-2013, 10:29 PM
Lots of schematics..:) He says as he adds one more. But you have the non-inverting one. Good.

Here is a simulation with a 60 dba spl. That's about like being in your living room listening to the TV. Maybe your tone is louder or quieter. I don't know. Anyway at that level you need more gain. So I took the bertus schematic with the filter and gained it up to where there is about 50 mv to the 9170.(see pot & resistor changes) Speaking of that what are pins 1 and 4 of the 9170 tied to now that you have the non inverting setup? :rolleyes:
Your op amp is ok - maybe a little fast for a breadboard so I added a 100pf cap across it so maybe it won't oscillate.
By bounces I mean echos in the room from walls and furniture and stuff.
You have a 5.5 volt battery?

ronv.

Which electret Mic capsule would you use.In a project like this.

I'm using a electret mic capsule from digikey P9925-ND. But its been replaced with another mic don't know the part number.How high should the
dba spl be to pick-up sound at 10ft...Is that signaltonoise ratio.:confused:

Which one would you use from digikey.com.

There is no 5.5V battery.Its a 6V.Its been used in other projects.

ronv
10-16-2013, 01:29 AM
Sorry, I missed you. The wm61a should work ok. I would just raise the gain like in the schematic. Seems your hookup is ok.

Etronic
11-01-2013, 04:46 AM
Hi

ronv

In bertus post #107 he changed the 10k bias resistor that i had in the original circuit.To a 4.7K, and used a 10uF decouple capacitor.

In your post you have a 2.2K resistor for the mic bias and a 100uF
decouple capacitor.Is there a differance in the function on how the
circuit will react to using the different parts.

Which parts would be better to use in the circuit.:confused:

ronv
11-01-2013, 06:22 PM
It probably doesn't make much difference. The 2.2k will raise the gain slightly and the 100 Ufd. will filter a little more noise out.

ronv
11-22-2013, 02:41 PM
Try turning the volume up and down to see if the distance changes. If it does the gain may still be to low.

Etronic
11-26-2013, 10:01 PM
Hi
ronv

At 1-2'' all the tones come on.And that's at the upper sound level on my computer.
Now at the same level.I move my computer 6'' away with the highest gain
on the amp.And some of the tones only come on and some don't.
The same thing happen's at maximum distance of 12'' still some come on and most don't That's at the highest sound level on my computer and the maximum gain
on the amp.
The trimmer pot is 100K. I'm using the circuit with the added parts that you added to my circuit in, i think post #108.The maximum gain with your added parts is a gain of 212.
Now i only have a 500K and 1M trimmer pot.What values would i need to get a even higher gain.With a 500K or 1MK trimmer pot.

But? i want to know why are some tones detected and come on.And some tones don't come on.This confuses me.Why is happening.

ronv
11-27-2013, 01:02 AM
I'm not sure why it doesn't work. It would only work on my telephone from about 2 inches and it was much louder than when I push a button on the phone.

Etronic
11-29-2013, 03:15 AM
I'm not sure why it doesn't work. It would only work on my telephone from about 2 inches and it was much louder than when I push a button on the phone.


my work up to 12'' But? some tones come on and some tones do not come
on the LEDs light up on some tones and not on others.

What happening here?:confused: Why do some tones and not the rest at 6'' and 12''. But? at 2'' all the tones work when i press each key on that keypad. And each LED comes on for each key that i pressed at 2''.

If there's anyone else out there who would know this and what could
be the problem please post to this thead.

rogs
12-01-2013, 04:51 PM
OK --it doesn't seem as if anyone is going to jump in here, so I'll try one last time.......

The reason your circuit is not working could be for several reasons.
The HT9170 (MT8870) is looking for two tones. One from the high group, one from the low. If it detects anything other than a valid pair of two tones, it will not update the output latches.

'Other' could mean noise, non-valid alternative tones, hum, reflections from the room ambience creating false tones....or a combination of any of those things. Because your unit is working close up , but not further away, then the one thing it probably isn't, is clipping.....

There is no way that any of us can know which of those is causing your problem, without either seeing an oscilloscope trace, or listening to a recording of the audio being received at the input of the HT9170.

Readers of this thread will know I have suggested, on several occasions, that you record and upload a sample of your received audio.

You just say you can't - and then move on to your next attempt at trying something different, without really knowing if you're even moving in the right direction.....it's called 'thrashing around in the dark'......

If you really are keen to get this working - and over 100 posts suggests you are - then post an audio sample of what you're getting at the moment.

Then we can all can hear what's going on with your prototype, and maybe offer some suggestions?.

Although this may seem like a simple project, it's actually not that easy to make a high gain, low noise audio preamp -- especially only using a 5V supply -- as a beginners project....

Post an audio sample....

Etronic
12-02-2013, 12:06 PM
OK --it doesn't seem as if anyone is going to jump in here, so I'll try one last time.......

The reason your circuit is not working could be for several reasons.
The HT9170 (MT8870) is looking for two tones. One from the high group, one from the low. If it detects anything other than a valid pair of two tones, it will not update the output latches.

'Other' could mean noise, non-valid alternative tones, hum, reflections from the room ambience creating false tones....or a combination of any of those things. Because your unit is working close up , but not further away, then the one thing it probably isn't, is clipping.....

There is no way that any of us can know which of those is causing your problem, without either seeing an oscilloscope trace, or listening to a recording of the audio being received at the input of the HT9170.

Readers of this thread will know I have suggested, on several occasions, that you record and upload a sample of your received audio.

You just say you can't - and then move on to your next attempt at trying something different, without really knowing if you're even moving in the right direction.....it's called 'thrashing around in the dark'......

If you really are keen to get this working - and over 100 posts suggests you are - then post an audio sample of what you're getting at the moment.

Then we can all can hear what's going on with your prototype, and maybe offer some suggestions?.

Although this may seem like a simple project, it's actually not that easy to make a high gain, low noise audio preamp -- especially only using a 5V supply -- as a beginners project....

Post an audio sample....

rogs!

Where do i connect the wire leads to the audio output of the amp or the input of the decoder.Please explain how to connect them.

I will try and record this audio signal. Thats if my PC records it.

rogs
12-02-2013, 01:19 PM
Connect pin 3 of the HT 9170 to the line input of your computer sound card, via (in series with) a capacitor. ( A mic input will probably be too sensitive)
Any capacitor in the range 1uf to 100 uf should do fine.

Use a free app ( like Audacity (http://audacity.sourceforge.net/) for example) to record your audio on to your computer.

Etronic
12-02-2013, 07:54 PM
Connect pin 3 of the HT 9170 to the line input of your computer sound card, via (in series with) a capacitor. ( A mic input will probably be too sensitive)
Any capacitor in the range 1uf to 100 uf should do fine.

Use a free app ( like Audacity (http://audacity.sourceforge.net/) for example) to record your audio on to your computer.


Keeping the LMV796 amp connected to the decoder.Correct! Or disconnect it.

rogs
12-03-2013, 10:32 AM
Yes..keep the op-amp connected.
You're looking to record from the output of the internal op-amp in the HT9170, which is the last stage in your amplifier gain chain.
That way we shall be able to hear all of your analogue input circuitry....