Allow adjusting PWM output range for lights, fan or heater channels

[EliotBR (Eliot)]

Hi @BStiles, welcome to the forum

@BStiles

We’ve tried tinkering with RC8_MIN, RC8_MAX, SERVO8_MIN and SERVO8_MAX, and monitored the values in MAVLink Inspector and on a scope, but the range of PWM output stays resolutely between 1100 and 1900us.

We’d kind of like to be able to map a joystick input of 1100-1900us onto a PWM range close to 0%-100%. 10 steps would probably be fine. Other ranges might be good for other purposes, of course.

…
we can’t find where this is implemented in the code or available in the QGC setup.

ArduSub’s joystick button function handling for Lights1 is here:

ArduPilot/ardupilot/blob/Sub-4.0/ArduSub/joystick.cpp#L246-L263

Somewhat confusingly, the output values are determined by the lights1 input channel range (rather than the SERVOn_ values for the assigned lights1 output channel, which are apparently ignored). That’s probably a bug, but for now you can set the values corresponding the the RC Input channel for the control you’re working with.

For Lights1 that’s RC9 (note the RC_Channels::rc_channel(8); in the implementation is zero-indexed). I’ve confirmed that setting RC9_MIN=1 (0 skipped the lowest step, 1 is still ~0% duty-cycle) and RC9_MAX=5000 (100% duty-cycle for a 200Hz output) or RC9_MAX=20000 (100% duty-cycle for a 50Hz output) allows whichever output channel is assigned to Lights1 (e.g. MAIN 8/servo 8 for your described use-case) to take on values in that range by checking SERVO_OUTPUT_RAW. I imagine that works fine for the actual outputs, but I’ll leave that for you to check with your LED or oscilloscope.

Number of steps can be controlled as usual by the Brightness Steps control from the Lights page, or the JS_LIGHTS_STEPS parameter if for some reason you want more than 10 steps.