The sound from the speaker makes a loop with the microphone
Temporary solution, using an iPhone (which has an algorithm for echo cancelling)
Paper and tape prototype, very light collar holding a (heavy) iPhone
Bought a bluetooth handset,
Wired a very first version of my circuit,
Power supply + sound amplification + big speaker,
Testing the bluetooth connection to the phone.
Thanks to Théo Reichel, technology superviser.
http://www.complex.ch/ – modprobe.complex.ch