Let's Make Robots!


Seek the brightest light in the room

Feivel was my very first robot. He's a little phototropic (light-seeking) robot built into an old computer mouse case. I'm nowhere near clever enough to come up with the simple circuit that controls him -- it's the classic 'Herbie' circuit by Randy Sargent, using an LM386 op-amp (originally intended for use as an audio amplifier) to read the difference in light level between the two infrared phototransistor 'eyes' and use that to split the voltage between the two motors. When both eyes are seeing the same amount of light, the 9V gets split evenly into 4.5V for each motor. When one eye sees more light than another, the op-amp directs more voltage to the motor on the opposite side, which makes the robot turn towards the light. The end result is that Feivel seeks out the brightest light in the room. It also has the added side-effect (as you can see in the video) that when he finds himself on a shadow with bright floor on either side, he'll tend to follow along the shadow, since neither eye wants to move into the shadow. Emergent behavior!

One surprising fact I learned while working on this robot is that, just like a motor will also function as a generator (and vice versa), and a speaker will function as a microphone (and vice versa), LED's also function as light sensors. Any plain old LED will produce a slight voltage across its pins when exposed to light. The 'eyes' on Feivel are actually the infrared emitters that used to be inside the mouse to determine the position of the ball -- it turns out that the emitters work better than the receivers as general light sensors. Crazy.

Since this was my first robot, I took a bunch of pictures of the entire construction process. Since I have no code or programming logic to share for this one, I'll just post some of those :)

Prototyping the circuit




Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Haha, yeah, probably scary. But I appreciate it all the same :)

Man, CowGod, I already love you :-D... You make some pretty cool robots!

Can't wait to see more of that kind.

- Jimmy

So THAT's what they are for:


- And no gears!?! Seems surpringly effective!

/ Frits

Aha. Yup, that looks similar to what I used. Mine were just the rubber feet from an old joystick that I pried off, rubbed off the sticky stuff, and poked a hole in them with a nail.

Now this is a fun robot! It's simple but with great effect. I really like it. In fact, this is my second favorite so far (after the YDM of course, nothing beats that beat). 


We don't stop playing because we grow old, we grow old because we stop playing.

Hey, thanks. And I agree about YDM, that thing is just too cute :)