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Topic: Microphone input help! (Read 2309 times) previous topic - next topic

plasmaninjaa



hello, I have been trying to make this circuit http://www.picaxe.com/docs/picaxe_sound.pdf

I have followed the instructions as best I can, however I get no input voltage from the input pin, no matter what sound. It always reads 0v on my meter and 0 in the serial port.

here are a few pictures of my circuit:

-http://i50.tinypic.com/15y9due.jpg

-http://i49.tinypic.com/2py2waq.jpg
-http://i50.tinypic.com/14wu4pi.jpg

unfortunately from lack of parts, I had to vary from the circuit slightly, perhaps one of these are the problem?

-2 100k resistors in series to make 200k instead of the needed 220k
-2 ~2nf caps in series to make ~1.3nf instead of the needed 1nf
-using the bc557b-4 transistor instead of bc558b
-using bc548-4 transistor instead of bc548b
- using polarized electrolytic caps might be a problem?


other than that, I cant think of anywhere I went wrong. Does anyone have any suggestions? I dont have access to an oscilloscope :/

any help is greatly appreciated!

Grumpy_Mike

What value are those capacitors? They do not look like 470nF more like 470uF. If they are too high then C4 will absorb all the sound you put into the circuit. The others do not matter as much but that one if it is too big will stop it working.

dhenry

Someone had trouble with that a while ago and sorted it out. You may search for that thread to see if it helps.

plasmaninjaa


Someone had trouble with that a while ago and sorted it out. You may search for that thread to see if it helps.



theyre all 0.47uf


Someone had trouble with that a while ago and sorted it out. You may search for that thread to see if it helps.



I looked for it and couldnt find it. do you have the link?

Grumpy_Mike

Quote
theyre all 0.47uf

Are you absolutely 100% sure of that? If so what is the working voltage, those capacitors are huge for 0.47uF.

plasmaninjaa


Quote
theyre all 0.47uf

Are you absolutely 100% sure of that? If so what is the working voltage, those capacitors are huge for 0.47uF.


yeah theyre 50v 0.47uf caps

rvasque

Can you signal trace and follow where the signal disappears?
re-check your wiring again.
Your transistors orientated right?  It's C-B-E  (with the flat side facing you).


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those capacitors are huge for 0.47uF.

I've used these kind of caps for a VU meter. They're available in this radial format.

dhenry

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Does anyone have any suggestions?


The first step in debugging would be to make sure that the dc working points are right. I would measure voltage on the key points (bias divider, b/c/e on transistors, diodes' a/k, etc. vs. ground).

Mark them on the schematic to help people see clearly where the circuit sits at idle.

plasmaninjaa

#8
Dec 18, 2012, 06:43 pm Last Edit: Dec 18, 2012, 07:22 pm by plasmaninjaa Reason: 1

Quote
Does anyone have any suggestions?


The first step in debugging would be to make sure that the dc working points are right. I would measure voltage on the key points (bias divider, b/c/e on transistors, diodes' a/k, etc. vs. ground).

Mark them on the schematic to help people see clearly where the circuit sits at idle.



here is a new picture with voltage readings from the point to ground: http://i50.tinypic.com/27zw8c5.jpg

both the pots were set to around 50% while measuring them.

I also realized that the two pins from the top pot were connected to ground instead of +v which I have fixed.




plasmaninjaa

should I go try some smaller 0.47uf caps that arent electrolytic?
anyone else have any other ideas why this isnt working? I'm assuming its a simple fix

dhenry

Quote
here is a new picture with voltage readings from the point to ground: http://i50.tinypic.com/27zw8c5.jpg


It is a lot more helpful if you mark the voltage on the schematic, rather than a picture of the actual wire-up: very difficult to read.

plasmaninjaa

i think I got it working. the diode was backwards -.- I thought the black line meant the flat line in the schematic... weird

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