Current Work
The Mobile Coaster operates by following a flashing (1kHz) IR LED on the user.
I use the variable resistor to tweak the frequency.
This signal is recieved by two IR photo transistors on the front of the robot.
The black bands you see surrounding the transistors is some shrink tubing. I did this so they would be more directional and damp out some of the ambient light
The received signal is filtered by a bandpass
circuit. The output is made into a clean digital signal by some Shottkey inverters.
Unfortunately, the circuit is a little unstable. It tends to oscillate sometimes. This is likely due to a combination of the breadboarding mess (it is a bit of a rat's nest) and the loose tolerances of the parts.
I intend to fix this by dumping this circuit altogether. I will be replacing it with a LM567 based design. Doing so will lower the component count and size so that I can actually use the breadboard on the Sumobot base. That, in turn, will allow me to remove a tier from the bot, making the center of gravity lower.
Okay. I have now fixed that circuit. It is still sensitive to noise but filters MUCH better now.
Here is a short film of it in action. The mpeg is ~2MB in size.
LED Detector
So far the platform looks like this:
The big black block is a 6V, 1300mAh, sealed lead-acid battery. I didn't feel that the four AA batteries would provide enough current to last driving around laden down by a full drink holder. Unfortunately, it is now even heavier! If I can find some rechargable AA batteries that have a high mAh (milliamp-hour), I will consider using them. One of the other advantages of using the sealed Pb-Acid is that I can charge it without taking the bot apart.
Let's talk code. The robot kit is based off a Parallax BASIC Stamp controller. The big drawback with this is that there are NO INTERRUPTS OR TIMERS... aaarrgh! So difficult to do even light duty signal processing and asynchronous control...
But that is what I have to work with and I am sure I can find a way around it. In fact, I have kludged some test code together that even works! Please keep in mind that this code is only prototype and is neither complete, pretty, nor entirely functional. I still have yet to add forward motion and collision avoidance, for example.
This code only detects and turns toward the LED emitter: Proto Code.
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