Need help troubleshooting sound-activated switch

Not open for further replies.

Thread Starter


Joined Jan 18, 2016
Hey all - I've been working on adapting a schematic I found here on youtube (versions of which seem widely available elsewhere).

I've successfully breadboarded a build of the above switch (version A in the drawing below). The only differences in my build (A) versus the above are the value of R1 and the fact my supply voltage is +9V instead of +5V. Even so, my build of the circuit works great. When I clap, I get DC voltage on the output of the 555.

The main alteration I require is to replace the electret condenser mic with an 1/8" input jack (which will be connected to the headphone jack of an iPhone). The schematic for the revised circuit is version B.

For some reason, however, as soon as I remove the condenser mic I get a constant voltage on the output of the 555 - there's no fluctuation and the signal from the input jack has no effect. I've experimented with the value of C1 in this version (the advice I was given was to work in the range of .01uF to .1uF) and every other variation I can think of to no avail. The circuit only works when the condenser mic is in it.

Does anyone have any idea how I might revise this design for use with a 1/8" jack? Or even a different design entirely? I just need the thing to work.

Ultimately I'm planning to run the circuit off +12V. I'll be using the output of the 555 to trigger a relay which will cause a solenoid to fire. I need the solenoid firing in time with a click track, hence the desire for an 1/8" jack. The solenoid is actuating the movement of a toy, making it appear to dance in time with a song.

I'd be most grateful for any advice. I'm happy to provide any more info that might be useful.

Thanks in advance!



Joined Jul 18, 2012
Look up the data sheet for the electret condenser mic. I think it draws quiescent current thus supplying bias for the first transistor.
Not open for further replies.