Hi folks, i`m doing my own little HDD Clock project and using the "LED sensor" method for measuring RPM.
The output waveform actually looks pretty good about 1.25V, at least up to ~6000rpm with a 2mm slit. Have not tried any higher speed.
What i`m unsure of is if the current generated in the led would be sufficient to drive a small BJT, say a BC237 or similar, without any biasing? Load will be an AVR input. Or would it require a schmitt-trigger?