I am looking at building a modular half bridge driver for various projects, and i would like to galvanically isolate that bridge from the controller, which is no problem for the digital control signals (gate firing signals) of course, but harder for the analogue ones. It struck me that i could use something like a Tiny to read the supply voltage and the device temperature (from an NTC etc) and then encode those values into a single digital (square wave) data stream where the frequency is dependent on the voltage measured and the duty cycle proportional to the temperature. That way, i'd get two channels for the price of one, so to speak!
Neither of those signals needs to be measured at high speeds, as both change relatively slowly, and they could both be decoded by a single pin (ICP) on the controlling micro after coming across an optocoupler for isolation. Neither need to be very high precision or resolution either. The supply voltage is not that critical (it is just used to prechargeing control and to modify the output pulse width as the DC link slowly reduces) and the temp sensor is really only used for "oh c**p somethings about to catch on fire" so again, no great precision requirements.
Is this a sensible approach? There will be some trade offs between duty cycle resolution and wave form frequency, but as the Tiny will just be doing this task only, it can run a tight software loop and not rely on any particular hardware timers etc. (although i may be better to use the PWM hardware for jitter reasons)
(i could also just put an isolated RS485 bus between modules i guess, but there is some justification for using a simple V to F convertor made out of a cheap micro)