function onTick()
  -- see stm32 reference manual to see which pins have DAC peripheral
  -- 1.5 volts on channel 0 which is always PA4 on stm32f407
  -- channel 1 would always be PA5 on stm32f407
  -- make sure that your firmware is compiled with EFI_DAC=TRUE
  setDacVoltage(0, 1.5)
  setDacVoltage(1, 2.2)
end