Hall Effect Tachometer

For measuring RPM and SFM (surface feet per minute). Based on a Motorola 6805 microprocessor and hall-effect sensor technology. The microprocessor code is programmed in assembly language and stored on an EPROM. A small bar magnet is fastened as a "T" across the end of the input shaft. Each pole generates a pulse as it passes by a hall-effect sensor. The pulse rate is measured by the microprocessor and the RPMs or SFM computed and presented on an LCD display. All functions are controlled with two switches. A toggle switch selects between very low and normal speed resolution while a momentary pushbutton selects the different calculation and display modes necessary for RPM or SFM display. RPMs are input with a cone shaped rubber tip. SFM are input using a small o-ring tired wheel of known circumference. Everything is housed in a custom machined aluminum case.