I am working on a project to find out the distance with 2 objects using radio waves. On one end we have a transmitter/receiver than sends a signal to another transmitter/receiver which spontaneously sends it back to the transmitting end. The first transmitter/receiver finds out the time it took for the signal to go and come back and uses that to calculate the distance between both of them.
The diagram below shows how it has been implemented by someone named Jones here. He uses counters, oscillators, dirty radios and a bunch of leds to show the results.
Not coming from a electronics background I am having trouble understanding parts labeled A,B,C of the Schematic Diagram which I have circled below.
Thanks for your help.