This old ( Bluetooth connected) phone Part 2:

Since the old carbon microphone was not operational anymore, I needed to up grade to a more modern approach for the BC127 module. I found an inexpensive electret condenser microphone. Working with these can be a little tricky and not quite straightforward depending on the gain of target application  and how much voltage you intend to run it off. Given that I am trying to run this all off of a 3 V source, I didn’t have enough amplification to directly drive the microphone into the input of the BC127.

This this little circuit came in handy:

I built the circuit on a solder-able  breadboard and tested it with an oscilloscope first.  I verified the circuit by  testing it on the prototype platform, currently resembling a mad scientist’s tangled mess of wires.

Success! A call made from my land-line to my cell phone paired to the purpletooth jamboree board connected to this kluge of wires, iron and alligator clips was rather exciting for a geek. I was able to test the microphone’s ability to pick up my voice from about 3 feet away before dropping off.

 

Next step: In part 3, I really want to ring an old time ringer which I purchased. This will requiring hacking into the code a little bit to set a GPIO active to engage the bell. The problem is that the bell will require a higher voltage too and may defeat my dream of being somewhat rechargeable and running off of a single battery and voltage source.  At the very least, I will test the connection to the switch which will engage the “answer” mechanism ( play button on the Jamboree board).