I have a quite simple task I can't wrap my head around. I have an old home 5.1 sound system with optical input that plays sounds from my media center. Its remote broke, and while I tried to fix it, I understood how much I hate having one more remote on my desk.
I'd like an microcontroller to "push" the required sequence of buttons to wake sound system up and make it switch to desired AV2 audio input.
I found service manual with schematic in PDF, it appears that buttons are just a "voltage ladder":
The device guesses which button was pressed by measuring the resistance (ranging from 200 Ohm to 1K). In theory I can easily solder 2 wires and apply the required resistance between them myself.
The problem is that I don't really know how to do that.
Do I need to make an array of transistors with similar resistors and close the circuit through required resistor one at a time? But won't the voltage drop on a transistor make this approach impossible?
Or should I use some form of analog output (PWM + "low pass filter")? But won't the voltage of my microcontroller fry the circuit of the audio system?
I can fit a relay board inside, after all, but it is stupid.
Please point me in the right direction.
(as far as I can understand, the circuit operates on 4.8V)