[Rajendra Bhatt] writes in to let us know about a nice simple IR bounce tachometer. The project uses a startUSB for PIC board and a 16×2 character LCD with a very basic Infrared bounce circuit.* Measuring either a reflective or non reflective spot in the rotating object, in this case a bit of white paper, the micro is supposedly capable of measuring up to 99,960 RPM (we think the paper might fly off at this point) with a resolution of 60 RPM. This is the same concept as a beam-break style tachometer but keeps all your electronics on one end of the spinning hazard.
The article also goes into detail about setting the PIC18F2550′s Timer0 register to enable 16-bit resolution.* The PIC is configured to turn on the infrared LED for one second, measure the number of pulses (through timer registers), and multiply that value by 60.* We would be more careful with the TMR0H and TMR0L counters as they have to be read and written in a certain order to preserve their values, but you’d need to be measuring upwards of 15,360 rpm to run into that error.
It is a quality writeup for anyone interested in learning about the start USB for PIC board, tachometers, or a new project. Thanks [Raj]!
Filed under: Microcontrollers, tool hacks
