I decided to build an infra-red object detection system using High Output IR LEDs. For the controller of the robot I used the Parallax BASIC Stamp I. The latest greatest version of the software, at least as of 10/9/98, gives IRBOT three modes of operation. The default mode just does object avoidance, fun in itself, but I wanted more. So I added two new modes that are based on the CDS photocells that change resistance based on light intensity.
irbot - schematic

These are mounted in the front of the IRBOT and angled outward at about 30 degrees or so. The current code now has the ability to be light avoiding (photophobic) or light seeking (phototrophic). The mode is selected by triggering one or the other IR sensor for two seconds when you first turn it on. The specifics are further down this page. If you want to build this too, my advice is get the Scott Edwards book above and a Parallax Stamp 1. 4 rev. D. The rev D comes on a carrier board so no other expense is needed to get signals to and from it. The Scott Edwards book comes with programming software for the Stamp and it also comes with construction details to make the programming cable you will need to connect the Stamp to your DOS machine. The book is about $30 and the Stamp rev D is about $35. You now have a BASIC language interpreting microcontroller. You now only need two simple integrated circuits, some resistors, some capacitors, and a way to tie them all together. All of these components may be obtained at your local Radio Shack. This circuit works by modulating an IR LED at 40KHz, which is the center frequency of the Sharp GPIU5 IR Decoder module. Check what you get at Radio Shack, some GPIU modules are 38KHz, which really, is close enough anyway. When the modulated IR beam bounces off of something the IR module will react to the signal by giving a logic low on its output. The logic of this circuit functions by first...

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