What's the fun of building this if someone spoon feeds you the circuit diagram?
Object chasing to me suggests you need video, like the CMUcam to be able to (a) recognize a color-coded object (b) determine what direction the object is moving. To recognize any generic object is rather non-trivial. To recognize a big orange spot on an object, using a CMUcam (not that I have done this, mind you, just based on what I have read/heard) is considerably easier and in reach of the hobbyist / amateur / etc.
**broken link removed**
You can pick one up at
Acroname among other places.
Something similar was intended for the FIRST Robotic Challenge 2008, I think -- kits included a color-sensitive camera and the trailers hooked to the robots had masts with color-coded flags so robots, during autonomous mode, could potentially chase each other / aim moon rocks at the trailer.
I suppose you could figure out a way to detect an IR beacon. That'd require, I guess, a bunch of IR detectors positioned to allow the robot to determine direction of the beacon. E.g., have a detector positioned on a circle, on a plane parallel to the 'floor' with ir becons aligned around the circle pointed radially, every, say, 15 degrees.
**broken link removed**
Or even a few detectors with a servo-mounted turret so it can 'scan'. The detectors could simply be IR phototransistors, or IR remote control modules that handle the detection of ~40kHz modulated signals.
Michael
PS: you could also create a simple light sensitive robot that steers towards light -- there are simple designs out there involving a sensor and motor on each side and the amount of light sensed on one side drives the opposite motor harder to steer the robot so the light is between both sensors. Like this:
http://www.geocities.com/lemagicien_2000/elecpage/ltch/ltch.html So then you just put a big light bulb on the robot being chased.