Do you have signal at the output of the op amp?
What pin are you monitoring on the HT9170?
What pin are you monitoring on the HT9170?
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.
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.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.
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.
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.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 since
my original thread had more of the circuits.info.
How long does the LED stay on when you power up the circuit? Maybe we can design a fix for you.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.
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.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.
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.I like to know what can i do to prevent the LED from coming on when i power up the circuit..
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!)Here is a circuit that should keep the LEDs off for about 1 second after power up.
I had pointed out the wimpy drive capability in post #84.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!)
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.The resistor connected to pin 16 will need to be more like 330KΩ. ( any value between 100KΩ and 470KΩ should work OK)
Thanks for the clarification, rogs. I sorta figured that was the case.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.
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by Jake Hertz
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