1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice
bill nahd

Distance trigger

Distance measurement without a microcontroller (BEAM).

  1. bill nahd
    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! :cool: