My friend wanted to control the level of his home stereo system built into his house. No problem. Sorta.
I bought an off the shelf Bluetooth audio receiver, ran that through this Remote Audio Level Control box. The box is USB powered. I used XXXXXXXXXXXX I2C digital potentiometers to control the level. I used a XXXXXXXXXX microcontroller. My friend is crazy and refused to use wifi….even though he’ll be streaming his music from Spotify. Okie dokie. Challenge accepted.
It turned out I needed a second board to be mounted in the 2-gang panel outlet. It measured the level of the standard potentiometers on the wall and checked the state of 2 switches. My friend is also crazy and wanted to be able to cut power to the amplifiers when not in use. So the 2 switches control relays to the audio power amplifiers.
I really wanted this thing to last 15+ years and I was concerned about scratchy pots. I wasn’t exactly sure how long the cable from from the panel on the wall was going to be to the amplifiers. So, I decided to put a XXXXXXXXXXX microcontroller in the wall and send a UART signal to the controller on the audio level board. This worked out pretty well.
Problem #1: I used Fosi amplifiers from Amazon. These use a TI TPXXXXXXXX chip for impressive efficiency in audio power land. I’ve built one very similar. When power is cut to the amplifier, these amplifiers pop HARD. When power is first given to these amplified, they pop HARD. It’ll blow the speakers eventually. It turns out the soft turn-on circuit only works from the switch on the amplifier. It’s a simple MOSFET with a capacitor on the gate. So my relay approach would not be possible. HOW DID I SOLVE THIS?
