Has anybody made one from scratch? I recently got into writing software for PIC microcontrollers (for work) and it struck me that one could be used to monitor a series of pulses from a spindle-mounted transducer and display the RPM on a 4-digit display.
The point I've got to so far is getting the PIC to display numbers and to increment a value if it parses an 'on' from a button. Next bit to do, software-wise, is to set up an interrupt to increment the counter without polling the switch. Should manage that okay, but I'd appreciate comments on how to read the spindle's rotation.
My thoughts at present are to use a hall effect device and a small magnet, with a spindle-mounted vaned disc passing between device and magnet. To get a decent rate of display update (10 per second seems okay), I plan to cut several vanes into the disc to ensure that there are several pulses per rotation. I haven't thought much yet about converting the output from the hall effect device into something the PIC can read, but gather they're low voltage (I saw 0.4V in the spec for one).
Looking to fit one each to my Clark CL300 lathe and Cobra Micro mill (Clark CMD10). Haven't thought about how to fit the discs yet, but somewhere inside is the plan. The PIC is the Microchip 16F628.