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I'd like to create a small device that can tell when it's near another created device or sensor. When it detects the other device, it lights up an LED.

Maybe maximum detection range of a few feet. No need for any unique ID values or complex data exchange, just a simple "Yes I detect one, no I don't" sort of control.

Any suggestions on how this could be done in a low power, portable sort of way? Because its requirements are so simple, something like RFID seems overkill (even if it could be made to work).

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You could use a simple Infra-red LED, and a photo diode. You may have to adjust the LED intensity with a potentiometer to calibrate the range.

This will sense proximity providing there is line-of-sight.

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  • \$\begingroup\$ Hmm hadn't thought of IR. Have to think about the LOS thing and if that's an issue... \$\endgroup\$ – Tim Holt Mar 30 '11 at 20:55
  • \$\begingroup\$ Calling this good - thanks for that brain nudge I needed BG100! The first circuit on home.cogeco.ca/~rpaisley4/PhotoDetectors.html (lights when sensing) looks like it would do what I need. \$\endgroup\$ – Tim Holt Mar 30 '11 at 21:25
  • \$\begingroup\$ @Tim Holt: No problem... \$\endgroup\$ – BG100 Mar 30 '11 at 21:38

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