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The BEAM Circuits Collection is a BEAM Reference Library site.

Contact sensors
Making contact

Contact sensors (as their name implies) require physical contact with some other object in order to "trigger."

While this is sometimes a bit inconvenient for your 'bot (unlike proximity sensors, contact sensors won't help a 'bot avoid an obstacle before it is within "arm's reach"), it has two big advantages:

  • Contact sensors are very easy to build at home from various bits & pieces you probably already have lying around.

  • Contact sensors don't draw power until contact is made.


Obstacle avoidance contact sensors

Contact sensors for obstacle avoidance are essentially the electronic version of a cat's "whiskers." In most designs, a whisker is attached to one electrical contact, and this contact gets pushed into another one if the whisker touches something. You can also just mount a "whisker" to a small pushbutton switch (you can salvage some nice "soft" ones from floppy drives).

Ian Bernstein's site has an excellent tutorial for one contact sensor design here.


Ground contact sensors

Some BEAMbots may want to know when a leg touches the ground. Here, you'll need some sort of a foot contact sensor. Again, you can use a "soft" pushbutton switch (preferably salvaged) for this job. You can also build a fairly simple ground contact sensor of your own.

Clifford Boerema, Jr. posted a nice design for a foot contact sensor.

Foot sensorI enlarge!

I drew up a similar design for a normally-open sensor, using a spent .22 cal cartridge (if you're a "plinker," you should be able to come up with lots of these).

NO foot sensorI enlarge!

It's normally-closed cousin is here.

Coming soon...

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Page author: Eric Seale
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