Udif entered the TTL based range finder into the Open 7400 Logic Competition. It uses an ultrasonic sensor to determine the distance to an object.

The sensor outputs a pulse, the width of the pulse is proportionate to the distance measured. The sensor signal drives a clock which in return increments a counter. The clock is timed so that each tick of the counter responds to 1cm of distance, and the output is shown on a 7-segment display.

Via the forum.