Simple tachometer for 1 to 99 pulses per rev
This tachometer is designed to be used with lathes, mill or other machine tools. If there in an existing gear wheel on the shaft whose speed is to be measured then it is simple to mount a hall effect gear tooth sensor close to this gear. The number of pulses per rev is set to the number of teeth on the gear. If there no gear then a single reflective marker (A piece of aluminium foil for example.) stuck onto the shaft or pulley with a reflective opto sensor positioned close by is probably the simplest. A hall sensor could also be used sensing a hole drilled into the rotating part. To set the number of pulses per rev the setup button is held down and the unit then powered up. When the button is released the current setting of pulses per rev (PPR) is displayed. If the button is held down again this value increments about every 0.6 of a second. When the desired value is reached the button is released. At this point the top segment of the left hand display is illuminated to show that the new value has not yet been saved. After about 5 seconds the value is saved to EEPROM and the segment is extinguished. At this point the unit is powered off to take it out of setup mode. Next time it is powered up it is in normal mode using the new value of pulses per rev.