Easy to build using only a few components. With some modifications, it can be used in an automobile. This Tachometer uses a PIC 16F628.(06/12/2004)
CODE: JP6283 - PIC: 16F628
This digital tachometer can measure up to 30,000 RPM (or maybe more, none of my motors can rotate more than 35,000 rpm). Here is the pinout information:
Pin 3 defines the Display type: Common Cathode or Common Anode.
Pin 4 is the signal input, you can use optical sensors (Fototransistors, fotoresistors, etc), magnetic sensors (Hall effect, reed switch, etc) or using a switch.
DO NOT CONNECT ANY SIGNAL DIRECTLY TO PIN 4. High voltages can damage the PIC. If the input signal is more than 5 Volts, Use a driver as TTL, CMOS, Amp Operational or Transistors.
The RPM are divided by 10 when displayed, That means, a reading of 1200 means 12,000 RPM.
Download the HEX code HERE
NOTE: Use only 10Mhz xtal and 22pf or 33pf capacitors.