Conception of an adaptative laser range finder based on phase shift measurement

The whole concept of a laser rangefinder, based on heterodyne phase shift measurement, is presented. Next to the optical head, an HF card is built to produce the two frequencies that are combined to give the measurement and reference signals. After amplification, with automatic gain control, phase-shift is measured by direct high frequency counting, with better than 10 bit resolution. An interface card is used for the first averaging treatment and direct connection to the parallel port of a PC computer. An easy adaptation of the modulation frequency, from some MHz to some hundred of MHz, allows fitting to the required resolution and range