REQ: Tach circuit for motorcycle (bargraph)

I would use a PIC 16F628 chip as the central processor interfaced to your cycle via a rare earth magnet & Hall sensor attached to the motor crankshaft. The PIC reads the magnet crossing the Hall sensor and counts time. At the next crossing the PIC computes the correct LED to light up the correct via program logic or a simple table. The 628 has enough I/O pins to read the Hall and light a ten segment LED bar display

I use the Hall from

and Radio Shack sells small rare earth magnets that can easily and reliably attached to a rotating hob or gear.

I am using a 16F628 and the Hall/magnet to measure RPM for a PIC controlled electronic ignition system for a 31cc gas engine for a R/C airplane. It does the job quite nicely. You do need a PIC programmer and the necessary software to program the chip.

I built something similar for the owner of a 1930 Benz. It uses Honeywell GT1 sensors picking up a signals from the bolts on the flanges that connect the driveshafts to the gearbox.

The processor is an Atmel AVR 2313 with 50 LEDs in a matrix configuration, (8 columns driven by a ULN200? and the rows driven by NPN's driven by a 4028 decoder. I had to add a FIR filter as the input turned out to be quite noisy.

Wim