Good Morning,

I have a project I want to complete, and half of finding the answer on the internet is knowing the right question to ask. I feel like I've been asking the wrong questions, so I apologize if the information is easy to find!

My project is as follows: The end goal is to build both a transmitting device that is small and easily hidden, and a receiver that is small enough to insert in a piece of costume jewelry or some other small object. The receiver would have to be able to detect the signal strength from the transmitter, and would have an LED output that would glow brighter the closer it came to the transmitter. I'd like to be able to set it up so the LED began to glow within 200 - 300 feet of the transmitter. Essentially a flashy version of hide and seek. I was thinking of building a little RF beacon, but I am stuck on the receiver. My thought was I should be searching for something that functions like a photosensor, but for RF waves - so the resistance in the circuit would decrease as the receiver got closer to the beacon - but I might be barking up the wrong tree. I was initially considering an IR LED and an IR sensor, but I was uncertain if that would have it's own complications - I don't know if staring at an IR LED for a half an hour or so while they closed in on the source of the signal would be bad for their vision.

Thoughts folks?

 

Some of the small transmitter and receiver pairs working on 315MHz or 433MHz (or whatever depending on the legislation of your location) have an RSS output.
RSS is Received Signal Strength and is the closest you can get to what you want, but other signals in that band (and noise) will show up as well and RSS isn't an exact measure where you can derive a distance from the amplitude.

You'd have to check the range possible yourself (200..300' might be optimistic with the cheaper models) and make a small circuit which translates a varying voltage to a varying LED current.