Digital Read Out Caliper Guage

By Kevin Timmerman

This is an electronic digital caliper to computer (RS-232) interface. This will work with the inexpensive calipers, micrometers and height gauges that are typically made in China. The connector on the measuring instrument will have 4 pins, and the owner's manual will typically describe the output as 24 bit 90 kHz synchronous. This does not work the name brand instruments - Fowler, Mitutoyo, Brown & Sharpe, etc..

The code contains examples of:
 * 9600 bps asynchronous receiver/transmitter
 * 90 kHz synchronous receiver
 * host command processing
 * tables for data and text
 * sending text to host
 * 24 x N bit fractional multiplication
 * 24 bit addition
 * binary to BCD conversion
 * BCD to ASCII conversion
 * ASCII transmission with leading zero suppression and fixed decimal place
 * operational mode set by jumpers or override by host
 * Use of watchdog timer

The circuit contains examples of:
 * +5V/-1.5V power from serial port
 * 1.5V to 5V logic level conversion
 * minimal PIC to RS-232 interface

P.S. An updated version is available at:

This board is available from Olimex