BEAM robots are microprocessor-less machines, invented by Mark Tilden, long ago. Maybe you've seen them on the big bad web or made one yourself. This is a little idea i like to share with all robotteers out there.
Distance measurement. Nice when your little bot has a microcontroller. But my BEAM has only a nervous network... Okay Baldrick, time for a cunning plan!
This little circuit (just one TTL ic does the job) compares the measured pulse with a (user adjusted) reference. A BEAM-backup-sequence can be activated if something comes too close.
For everyone who needs it!
The core element is the cheap US-100 sonar module (there are more, look-alikes). Google for "gizmo us-100 sonar" and find the pdf. The principle working is easy. Apply a pulse on the trig input and the echo output will throw a pulse length according the distance of an object; 60μs per cm. With a μProcessor you would measure the time of this pulse to get the distance.
But with my little BEAM, i do not need the exact distance, i just want to know if something gets too close.
It is made with the 74123 dual timer ic (TTL). The first timer is triggered by the US-100 (pin2) and starts a reference time. Let's say about 600μs (~10cm). The second timer 'compares' the original pulse and the reference pulse. If the reference pulse is longer than the US-100 pulse, than the second timer is triggered. And this can activate a backup-circuit in a walker or photovore or so...
Tested and working. As said: for everyone who needs it!