How to use a transducer?

theamber

Joined Jun 13, 2008
323
I think you just need to build an amplifier in order to make it noticeble to the input of your device. Then you need to experiment with it to see if is sensitive enough for your application.
 

Audioguru

Joined Dec 20, 2007
11,249
It doesn't say but I think it is a piezo type.
Its sensitivity is poor and will need a lot of amplification (hello noise) but its allowed output pulse power (at 140Vp-p!) is high.
 

Thread Starter

sitech

Joined Jul 3, 2008
23
So basically I just send a strong pulse through one and expect to see a pulse come out of the other one (presumably after amplification).

I'm practically a beginner at all this, is sending a 5V pulse through the unit (since I have access to a 5V source) sufficient and then amplifying the receiver output to have a high of 5V? I can imagine I could just have a simple transistor amplifier circuit for that?

If I need an amplifier on the sending end, what would I use since I only really have a 5V source? For the receiving end is there a more elegant solution to amplification?

As I said earlier, my knowledge on electronics is very very limited (this project is as much a practical application as a learning exercise!)
 

theamber

Joined Jun 13, 2008
323
It doesn't say but I think it is a piezo type.
Its sensitivity is poor and will need a lot of amplification (hello noise) but its allowed output pulse power (at 140Vp-p!) is high.
From the little info that you supply I can figure out this.
It looks to me that it is a piezoelectric microfone and looks like you want it to send and audio signal to your device in order to make your device follow a particular audio signal (making the transducer a sound switch).
The transducer must be capable of producing a reasonable sound pressure for it to be "hear" by your device.The pressure levels in the room never has to exceed the operating range you gave it. I asume that you want to activated it by any sound, or of a particular level or else you will have to determine at what frequencies you want the transducer to trigger your device. I think for this application a high sensitivity is desirable. If you want to eliminate a particular noise from entering the mic. then you can built a band pass filter and then only a specific frequency will reach your device in order to activate it. If you know the input sensitivity of the device you want to connect it to, you will know how much amplification you need to obtain. I think I saw at www.parallax.com an audio direction finder of some sort. According to tone, frequency, and sound pressure it will act. If it is ultrasonic then you may have to activate it with frequencies above 20Khz.
 
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theamber

Joined Jun 13, 2008
323
Check this page I found a circuit for your application. But it has a two stages amplifier.

http://www.electronic-circuits-diagrams.com/audioimages/audiockt10.shtml
If you are not comfortable building this I think I have seen units like your mic. that have a built in amp and just output a 5V dc when it is stimulated by a particular frequency,tone or a particular power level, so you just have to only connect it to the input of your device without building nothing in between. If you do not have it yet I suggest you get a simulation software like Electronics Worbench or Circuitmaker before you buy the parts and build it by real.
I hope this helps.
 
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Thread Starter

sitech

Joined Jul 3, 2008
23
Thanks for the help!

I'm assuming I have to give it a 40 KHz signal. I'm pretty sure the Arduino can do that effectively and it only has to be done for a pulse. Otherwise I can get that 555 chip in the example circuit and use that.

Thanks for the example circuit! I'll have to read up on amplifiers to see how they work and use that!

The transducer can be a receiver and a transmitter, so I plan to have one as receiver and one as transmitter :)
 

Thread Starter

sitech

Joined Jul 3, 2008
23
Anyone have any hints on how to calculate the required amplification based on:

Transmitting Sound Pressure Level: >105 dB
Receiving Sensitivity: >-74 dB
 

Audioguru

Joined Dec 20, 2007
11,249
The spec's for the transmitting trancducer is 105dB at a distance of only 30cm when it has a p-p signal that is 5.7 times more than your 5V supply. So its output will be only 90dB at 30cm.
 

theamber

Joined Jun 13, 2008
323
Anyone have any hints on how to calculate the required amplification based on:

Transmitting Sound Pressure Level: >105 dB
Receiving Sensitivity: >-74 dB
You can do the math or use one of the calculator all over the net already programed for that.
Look at this:
http://www.sengpielaudio.com/calculator-amplification.htm

Also, be carefull about the limits because if the amplification factor is too high, the slightest feedback can trigger oscillation, rendering your amplifier system inoperative.
 

Thread Starter

sitech

Joined Jul 3, 2008
23
Thanks!

I've been reading the eBook attached to this website.

Can anyone else suggest any other reading material? I know the basics of electronics up to transistors (through physics and tutoring people on the topic), but applying the theory is another matter.

Thanks
 

theamber

Joined Jun 13, 2008
323
If you have read Lessons in electric circuits then I will definitely will suggest you to read "The Art of Electronics" by Paul Horowitz. It has a very different approach to electronics designs and tells you what to do and what not to do when designing circuits. You can probably download this via a bittorrent.
 

Thread Starter

sitech

Joined Jul 3, 2008
23
Thank you for the suggestion of that book! It is excellent!

Been trying to make the transmitter with a 555 chip. I've got it outputting ~40 khz square pulse.

Now my idea was to just have the output going to the base of a transistor (like a BD139) and having the transducer on the collector side and a resistor to control the current on the emitter side.

Looking at this:
http://www.electronic-circuits-diagrams.com/audioimages/10.gif

The creator of the system has a more complicated circuit, which I'm unsure about. He uses two transistors with diodes as if there was a negative voltage coming out of the 555 chip, but AFAIK the chip is only outputting a square wave where it goes from 0v to ~9v?

The creator also has the speaker on the emitter side and the ground of the speaker in a voltage divider. I assume, if there IS negative voltage, this would allow it to swing either side of 4.5V, but where is the negative voltage?

Also, this may be an obvious question, but when i measure the output of the chip its about 2.5V ( i assume 0-5v, but just oscillating too fast for my multimeter), when I stick the transistor in, it drops to 0.4V at the base. I assume it has something to do with load resistance, but I'm not sure.

I've tried placing speaker on the collector and the base gets the expecting 2.5V

Can anyone help me understand whats going on? I know its probably obvious the answer, but I don't know much on the topic.
 

yubyub

Joined Aug 13, 2008
19


This diagram might help explain things. Essentially on the transmit side, the transducer is held at the 'middle' voltage so that oscillations from ground to Vsupply, on the transducer look like a +'ve and -'ve voltage.

This trick isn't neccessary when receiving because you can amplify the signal to a voltage range you want to use.
 
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