Have you ever wanted to determine how fast something was turning? With a few parts and a microcontroller, monitoring something spinning is a simple task, you just need a way to get an input into the microcontroller so it can count pulses. In this case Chris from Pyro Electric used an infrared beam to monitor a spinning fan, as the fan blades turn they interrupt the IR beam made using a IR LED and a IR transistor.
Read about the DIY PIC Microcontroller Based Digital Tachometer Project.
“The IR circuit will output pulses whenever it is interrupted (this type of IR circuit is also known as a ‘photo-interrupter’ circuit). The PIC microcontroller will stand by waiting to see the rising edge of one of these pulses. Anytime a rising edge is detected the PIC will interrupt the current software and run a special subroutine to take note that the change on the signal occurred. Now, if we keep track of how often that change occurs using a timer, we can estimate the instantaneous RPMs, making a digital tachometer!”
