How would one build a device that follows/is attracted towards a signal(IR, RF, etc.)?

Hello, what is the simplest way to control a device so that it is drawn towards a certain point? I'm sure there is already an instructable on such a device but I can't seem to find it. Sound or voice control, line following, and light following(except maybe IR) won't work. Any guidance would be greatly appreciated. Thank you!

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AndyGadget8 years ago
Forget radio - It would be very tricky!

THIS Instructable is not particularly detailed, but it gives you an idea of the sort of thing you'd want.  The circuit is designed for visible light, but if you replaced the LDRs with infra red photodiodes it should home in on a TV remote or a simple battery / resistor / IR emitter diode circuit. 
The variable resistors should be set so the motors are just below the point of turning on in normal lighting, then when light hits one of the sensors, it starts the motor on the other side turning, thus travelling towards the light.
mytleviathan (author)  AndyGadget8 years ago
Thanks! I'll give it a try!
lemonie8 years ago
These things ain't simple. You can get devices to "home" on radio, but it's not easy. Do you have a specific requirement?

mytleviathan (author)  lemonie8 years ago
Well the idea is to attach something to my belt that a cart would follow around. It would be operating in a loud, populated environment, so thats why light and sound wouldn't work as a good source of attraction. Any ideas or resources to get me started would be wonderful though. Thank you for your help!
If you use radio, you've got ranging and direction to use. But this is not going to be easy, think about aero-navigation systems & autopilot. Start reading, e.g.:

AndyGadget8 years ago
You're mentioning a lot of things there, but for all of them the general principle would be the same (with varying degrees of difficulty).
Mount two suitable sensors on the front of your device so each has a 'field of view' for 30 degrees or so over to it's side, but with some overlap directly ahead.
Your control circuit would compare the level of input from both sensors, and move and turn towards the one from which it received a higher signal.
This way it would home in on the source of the light, sound, IR etc.
Basically, you're giving your robot stereoscopic 'vision'.
mytleviathan (author)  AndyGadget8 years ago
What do you think would be the easiest way to do this? I'm just trying to get a cart to follow me around but I don't want to shine a light at it or yell at it, thats why I was suggesting IR or RF signals. I didn't know if IR or Rf could even be focused that well. I've seen the conversions that people have made to irobots/Roomba Creates, but it seems like it could be done a lot simpler. I don't even care about obstacle avoidance. Do you know where I could find a wiring diagram or anything to get me started? Thank you so much for your help!
seandogue8 years ago
I don't really know if there is an IR tracker instructable, but the concept is relatively straight forward.

use two receivers oriented at 90 degrees from one another to generate an error voltage for your guidance system.