The spark coil and injector drivers

As far as My16M is concerned, these four output are handled identically. Both represent a highly inductive load. The injector coil required about 1 or 2A to activate. The spark coil takes about 5 to 6A to activate and furthermore the voltage kick when turning off the spark coil current is around 400V. I have used the MTP6N60E FET as it can handle a continuous current of 6A (18A pulsed) and can withstand 600V. It has an inbuilt diode for protection and at AU$5, a bargain. The following circuit is used for all 4 coil/injector outputs.


The FET requires about 10V to turn on fully so an extra stage of buffering with the BC549 is used to raise the microcontrollers 5V to the 12V of the bikes electrics. The BC549 is normally held on by the microcontroller, thereby holding the gate of the FET at 0V. This leaves the FET off. The microcontroller sends applies 0V to the BC549's base turning it off. This allows the gate of the FET to go to 12V, turning the FET on and drawing current through the spark coil/injector