Years of experience are not important, but they need to be able to work semi-independently, learn quickly, solve problems, etc. So usually this is at least 3 to 5 years of experience for talented engineers)
Expert at low level C coding for bare metal architecture (custom round-robin, interrupts, configuring io registers, time critical control loops at 10 msec and 1 msec, PWM control) pretty much an old school firmware/embedded software engineer with an EE degree.
Experience implementing control loops for basic PID up to more complex control algorithms
Experience reading hardware schematics and debugging embedded software on the HW with debuggers, oscilloscope, function generators, DMM, etc
Location REMOTE
Nice to have experience modeling control algorithms in Simulink