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[on:]

Hi! First off, thank you so much for any help. I am slowly learning electronics and arduinos etc... maybe one day I will be smart enough to help people on here.

I am attempting to build the audio detection circuit found here: http://www.picaxe.com/docs/picaxe_sound.pdf

I arranged it all on a breadboard and I thought I did everything perfect...
I am powering the circuit by the 5v from the arduino.
The output (0-3v) is connected to an led. presumably the led should turn on when the circuit detects sound.

It does not turn on at all no matter what sound is made. I have tried changing the sensitivity of the two potentiometers. I have also hooked up the output to a multimeter.
it reads 0.52v no matter what sound is made or setting of the potentiometers.

Here is a high quality picture of the set up. Since some of the pins under the transistors and capacitors cannot be seen, I drew them in orange: http://i50.tinypic.com/r877r6.jpg

here are a few more pictures at different angles:
http://i45.tinypic.com/33dcs1z.jpg
http://i48.tinypic.com/18omdv.jpg
http://i46.tinypic.com/28vrvgn.jpg


Let me know if you have anymore questions.

Thank you for any help!

James Hutton

[Reply #1 on:]

a few tips:

1) power it up for the first time through a 100ohm resistor, and measure the voltage over that resistor: this assures you if there is short.
2) you need to make sure that the dc working points are correct. Measure voltage on Q1's b / c, Q2's b/e/c, Q3's b/e. and compare them to what you expect. For example, Q1's b should be about 0.7v, Q2's b should float with RV2, etc.
3) if you have a scope, it would be helpful but get the dc working points and report back.

[Reply #2 on:]

a few tips:

1) power it up for the first time through a 100ohm resistor, and measure the voltage over that resistor: this assures you if there is short.
2) you need to make sure that the dc working points are correct. Measure voltage on Q1's b / c, Q2's b/e/c, Q3's b/e. and compare them to what you expect. For example, Q1's b should be about 0.7v, Q2's b should float with RV2, etc.
3) if you have a scope, it would be helpful but get the dc working points and report back.

ok,
 
1) I measured the voltage over a 100r resistor in place of the led. It was 0v. I asume this is what you mean telling me there is a short.

2)    -i measured the voltage across q1. it reads 0.230mv from c-b, 0.6v from b-e and 0.85v from c-e.
       -q2: 4.5v from c-b, 5v c-e, 0.5v b-e
       -q3: 4.8v c-b, 5v c-e, 0v b-e

3) no scope :/

thanks!

[Reply #3 on:]

1) no idea what "led" you are talking about.

2) the voltage I was talking about was the respective points vs. ground.

[Reply #4 on:]

So Q1 is conducting, at about 0.8ma Ic. That's good.
Q2 is not conducting: RV2 is too small so you will need to raise the wiper towards the top (the rail).
As Q2 is not conducting, Q3 is not conducting.

[Reply #5 on:]

You need to raise RV2's wiper so that Q2's vbe goes towards 0.6-0.7v and Q3's base goes above 0.7v.

[Reply #6 on:]

1) no idea what "led" you are talking about.

2) the voltage I was talking about was the respective points vs. ground.

1) i meant from the output (0-3v) to the ground.

2) oh ok, sorry.

       q1: b = 0.63v  c = 0.86v
       q2: b = 4.5-6.5v (depending on sound)   e = 5v   c = 0 - 3.5v (depending on sound) (the led lights up to sound from this pin to ground, but it doesnt have the slow decay which i am assuming is what the next transistor is for)

       q3: e = 0v (no matter what sound), b = 0v (no matter what sound) c = 0v (no matter what sound)

so I am assuming the problem is somewhere around the last transistor...

[Reply #7 on:]

You need to raise RV2's wiper so that Q2's vbe goes towards 0.6-0.7v and Q3's base goes above 0.7v.

ok, the rv2 is at max and the vbe is 0.63v, but q3's base to ground is still like 300mv,

[Reply #8 on:]

If the circuit is powered at 4.5v rail, how can Q2's base go to 6v?

[Reply #9 on:]

In that event, R5 is too high. Get it down to ~100k.

[Reply #10 on:]

i turned the diode around and it seems to work now. weird. i thought the black line was the cathode. doesnt it look right in the picture?

[Reply #11 on:]

The circuit will work only with the diode as connected (in the schematic).

You can check for the diode's polarity by measuring voltages on both ends.

[Reply #12 on:]

OP, after you learn how transistors work, the next step is discovering that opAmp circuits
are a much better way to go, in general requiring far fewer components, and producing much
better results with a lot less effort,

http://www.google.com/search?&site=imghp&tbm=isch&source=hp&biw=1012&bih=811&q=electret+amplifier

However, it's always good to learn basic electronics, in any event.