I like to see if I can monitor the strike voltage on a lamp by a ballast, the strike voltage is about 1400V, using R1 to be 1M ohms and R1 to be 2.2k ohms on the divider I should see about 3.0V on the MCU's ADC pin, this looks workable but the most I have tried and seen working was 300V in theory this should work. Anyone have any experience on this?
Your MCU is probably loading your divider making your calculated values incorrect. You could use a high impedance FET op-amp to buffer the divider or account for the MCU load with your calculated voltage divider.