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 :)
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.
Aha. Yup, that looks similar 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.
One place you can often find 5V relays is on old computer modems. They were used to switch the signal between the telephone jack and the modem jack.
But it’s true, the relay isn’t needed for the general “run around and chase light” operation of the robot – it’s part of the circuit that backs up if it runs into something, but I found that I didn’t have space to glue on the ‘whisker’ that would trigger the bump switch on mine, so I’m not even using that whole part of the circuit. If you don’t want the robot to be able to back up when it runs into something, then you can leave off a lot of the components – basically everything up at the front of my robot (the relay, capacitor, resistor, transistor, switch…).
The original circuit designed by Randy Sargent is available from Solarbotics: http://downloads.solarbotics.net/misc/herbie.txt . It’s just like you’re asking, just the op-amp part without any additional circuitry for backing up. Hope that helps.
That image is great. It really makes it clear how the op-amp is controlling the two motors.
BTW, as far as adding lights, one modification I read about (assuming you’re using light sensors that are sensitive to infrared light, like IR phototransistors) was putting an IR LED on the tail of the mouse, then building a second mousebot. The second one would tend to be drawn towards the big bright IR light on the butt of the first one, so he’d follow around the first one As long as the IR LED is pointing backwards on the first robot, it shouldn’t affect the light sensors on the front.
pretty cool mouse bot!! I been wanted to build one of these for a while and i was thinking,
is there any possibility you can use a dpdt miniature pc relay 12vdc coil will these burn out the little hobby motor’s 1.5-3vdc motors using a 9v battery?? just a question looking a answer. Thanx . And your Feivel packs a punch fast little mousy.
but instead of detecting light I would like to construct it to seek out a flame (i.e. a candle). Now I was wondering, can I do that simply by replacing the photodiodes with some type of sensors that detect fire? I think it would work but I’m not 100% sure. Let me know what you guys think. Thanks
You will need a thermal sensor. I have no clue to electronics, I just buy pre-made boards and put them to work with each other… And so I have no clue what your schmatic should tell me.
Er, did you watch the video I posted above? I’m not sure if I’d want to set a skittering robot chasing after a candle. What do you imagine will happen when it finds it? House burns down
The circuit works by comparing the voltages on each of the two diodes, so you should be able to drop in any sensor that varies its voltage output based on what it senses. If you use something that varies its resistance, then you’d need to use it in a voltage divider to produce a voltage change.
awesome! now I can give it awesome! now I can give it a shot. I plan on making a basic firefighting robot. It will seek out a candle flame and blow it out with the help of a fan. I’ll let you guys know how it comes along. Thanks again Dan and Frits! really appreciate the input!
