Herbie line follower

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Schematic for "Herbie"
Schematic for "Herbie"

Herbie is a fairly simple creature, with two light sensors and two motors. Herbie's only "brain" is an LM386 audio amplifier.

Depending on the state of Herbie's DPDT slide switch, he is either attracted to or repelled by light. Just adjust the trimmer until Herbie doesn't prefer one direction over the other too much.

It's pretty easy to hook up a few LED's facing downwards and turn the photocells downwards, put some black tape on a white floor, and make Herbie into a line follower (finished dead last the timed light following contest at the Seattle Robotics Society Robothon in April of 1996.


2 low-current (< 100 ma?), geared motors (there are sometimes hard to find).
2 CDS photocells
1 10K Trimmer
1 DPDT slide switch
1 LM386 audio amplifier

Note: To increase the gain on the amplifier from 20 to 200, you can connect pins 1 and 8 of the amplifier together (with just a wire -- the app notes for the chip say use a capacitor, but that's only if you want to drive a real audio load). This makes the bot respond a little more crisply to changes in light.

Note: Long time BEAM supporter Solarbotics sells a Herbie kit that is enhnced with functional whisker and tail sensors, so that it will be less likely to get stuck in corners.

[edit] External References

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