Echo/Pitch Shifter megaphone
The entire device (megaphone and sound manipulation circuitry) are all battery powered off the same supply so I had to use a connection cable between the phone and control box which could send audio and power.
It passes audio from the mic on the phone down to the audio circuit, then send it back up to the phone amp and speaker. I also had to send power from the phone batteries to the sound circuit. I used an insulated XLR cable which worked well.
Old schematic below as of 2008. lots of weird stuff going on in there… but it took me a long time to hand draw and its fun to look at so I’m including it anyway: