Atmega328P bootloader for use with GRBL using the spindle direction as spindle enable option.
*Optiboot bootloader github: https://github.com/Optiboot/optiboot
*GRBL github: https://github.com/gnea/grbl
Running grbl V0.9 and above you can use a compile time option " USE_SPINDLE_DIR_AS_ENABLE_PIN " to turn your router / spindle on or off via a relay using G-code ( M3 / M5 ) over the Arduino pin D13 while leaving variable spindle pwm on Arduino pin D11.
This can have the effect of our router / spindle relay being triggered every time the atmega starts up or resets due to Optiboot flashing the led that resides on arduino pin D13. Not a behavior we want in our cnc. To fix this we can run without a bootloader and burn grbl over icsp or update Optiboot to change this behavior.
This is a repository for Optiboot 6.2 compiled using the following command to disable the flashing led on Arduino pin D13. “make LED_START_FLASHES=0 atmega328”