I an VERY poor at C programming so someone else will be better to comment on the software. (I would have written it in assembler and used an Attiny13A.)

Les.

I am very poor at C programing and haven't a hope with assembler. But agree when the logic and all signal filtering is all sorted out I will find someone who knows how to put it in a nice neat package with automotive quality, durability and minimal hardware. And that could be you or anyone else on this sight that might be interested.

 

Interesting results today. I received my new Yourdrino RoboRed board. Testing showed that with the MOSFET installed and running at 5V, the new board would reset itself without the need for using the reset pin and capacitor as required with the old board. Testing also showed that running the fan direct 5V PWM signal both new and old board required the reset pin and capacitor to reset. Testing at 3.3V with the MOSFET,does not required the reset pin and capacitor for both the new or old board. Note that running directly at 3.3V without a MOSFET cannot be performed because the voltage needs to be above 3.8 for the fan to run.

In conclusion I cannot say if I damaged the old board or are they operating on the edge of where they reset by themselves or not, and just a small differences in the boards could be putting one over the edge. But I believe the cap and reset pin is probably prudent to use.