I want my Teufel e450 to automatically turn on when Echo dot starts playing music. With its capacitive touch buttons and glue sealed housing, there is no simple way to hack it direcly into the device. But luckily it comes with a remote control at least able to power on/off, select next audio source and volume control.
The Teufel Puck-Control uses a NRF51822. I first have tried to figure out the wireless protocol, but without success. So I ended up cloning the firmware (luckily there is no read out protection enabled) onto a cheap NRF51822 board and hooked it up to an ESP32, which then is controlling the "buttons" by setting the input levels. The rotary encoder is emulated by a simple state machine.
For audio level detection I use a coupling capacitor connected between the line-out and the ADC and used a high pass filter feeding a low-pass-filter which then triggers the turn-on-command when hitting a threshold value.
Quick & dirty hardware. small pitch of NRF518022 module requires magnet wire