My first "real" computer was a VIC-20. I used an optical detector hooked up to the joystick's ADC input to observe that my fluorescent lamps were not "steady"

My first "real" computer was a VIC-20. I used an optical detector hooked up to the joystick's ADC input to observe that my fluorescent lamps were not "steady" but instead flickered at some frequency. I became an embedded computing guy later on... :)