Looking to give the Lua interface access to the on-board ADC. Giving methods such as get_voltage and specifying which channel (6.6 or 3.3). Not sure how to go about this, looking for what steps to take to add this custom binding
The Lua documentation is here
https://ardupilot.org/dev/docs/common-lua-scripts.html
You can actually do this already if you go via a battery monitor. You can enable a battery monitor using the pin you need and setup the scaling if necessary. Then you can read the voltage from that moniter from lua uaing:
battery:voltage(instance)
You will need to turn off the failsafes for and warnings for that battery monitor.
So we are using a Pixhawk Mini, there is already a battery monitor being used via the Power input port. So would this be me setting up another instance of BatteryMonitor, and linking it to the pin corresponding to like ADC 6.6V?
yes, exactly right, bit of a workaround but should work fine