i spent some time cleaning up the new s.bus controller code and making sure it reads channel pulses accurately. it does and can be used at this point. the benefit of switching to s.bus is that reading channels no longer requires an interrupt routine. i can now use the interrupt routine to read the RPM pulses without concern of an interrupt happening while insude another interrupt routine (which would prevent the interrupt from being recognized and the rpm pulse would be lost).

the s.bus signal needs to be inverted before going to pin 7 of the seeeduino xiao and that can be easily accomplished using a transistor and 2 resistors or, even better, one channel of a uln2003a and a single resistor. i'm leaning towards the uln2003a solution because it can also be used to buffer the solenoid signal without any added parts which reduces the total part count bcause it eliminates the mosfet and resistor we currently use. it also reduces cost as the uln2003 is about a quarter the price of the mosfet we've been using.

i'll be adding RPM sensing to the controller and using another channel of the uln3002a plus a resistor for that. i also plan to add the air pump control (using yet another channel of the uln2003).

'll use 2 channels of the uln2003a to control a high current power supply (such as to power the ignition which would eliminate the cost of the opti-kill switch and it's required channel input). i plan to thoroughally test this to make sure there's no interference from the ignition but we already connect the RPM signal to our telemetry devices/radio without any isolation when we use openxsensor devices without issue.

there's one more channel on the uln2003a available for future use and i'll not connect it at this point.