Sound detector

T

taux3

Member
Dear all,

I 've made the sound sensor circuit as suggested by the picaxe site under the 18X datasheets.
Unfortunatelly all I am getting through my multimeter as an output is 0 volts no matter how I adjust the pots. Is there a way to troubleshoot the circuit without an oscilloscope ? There is no circuit shorting and I am using a clean 5V DC supply. Mic polarity properly inserted (I am getting about 0.6-1V across the electret microphone)
Any step by step troubleshooting instructions would be great.
(I am more into digital elecronics and I am having troubles with this analogue circuit)


Best Regards
Antony
________
yamaha wiki
 
Last edited:
M

Michael 2727

Senior Member
If you remove the microphone you should get the full supply
voltage e.g. 4.5V across the terminals, R1 only limits the current.

With the microphone removed try touching the Pos+ Mic input
and with a speaker connected via a 1µF to 10µF series
capacitor (in Line), between the output and Earth/0V.
Or a Piezo straight across Output & Earth/0V.
This should produce something, hum noise etc.
A 1V Peak to Peak signal injector would be even better.
( you can prolly find a few on the Web, they ca be as
simple as a 1 or 2 transistor circuit )

If you have no tools test gear a finger is a good input
source at a pinch (NOTE: Low VOLTAGE ONLY PLEASE ! )

Try touching the base of Q3, Q2, Q1 working backwards
till you find the stage that is not working.
All this while you have a speaker or peizo on the output
to hear whats going on.

A Multimeter is not very good tool to measure sound
or audio outputs, in any way shape or form.
( see the notes on C4 values)
A CRO or a Speaker and Ears do a much better job.
 
Technical

Technical

Technical Support
Staff member
Most likely issue is a c-b-e swap up on one of the transistors - both NPN and PNP devices are there.
 
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