Finally, a complete schematic and working audio output

A project log for Classroom music teaching aid

An interactive device for helping a kindergarten class learn to play harmonica.

shlonkinshlonkin 04/14/2016 at 14:170 Comments

It's about time I got an actual schematic on here. This is likely to change a little as things develop.

I've also got the audio output part working now.

I am pretty new to audio circuits and the little I do know comes mainly from datasheets and schematics. After several frustrating hours trying to design an audio output circuit with the parts I had on hand, I picked up a hammer and chisel and took out my frustration on an old portable stereo from a garbage pile. Amidst the resulting plastic rubble and circuit boards I found just what I was looking for, the power amp circuit.

It's a pretty simple circuit that was designed to run on 9V and has reasonable quiescent current of about 20mA(compared to some of my larger amps that were over 100mA). The next task was to remove it from the rest of the board, so after carefully following all the relevant traces, I marked out the section I need. Then I grabbed a utility knife and pliers and recklessly scored and snapped the board, crushing unimportant components and tearing leads from things that got in my way. The result is not pretty, but everything I need is intact.

Just to make sure this would work I rigged everything up and plugged it into the headphone jack on my computer. Everything worked well. This is encouraging.