The three stages of Promimity

I am looking to build a treasure hunt system where people wear a little receiver on the arm which starts beeping when you get close to the object / turn yellow. As you get closer, the beeping get's faster or the colour changes to red. Could I test RF transmission quality? I don't want to use GPS as that is very expensive!
Thanks

Nick

Yes, RF signal strength is an option, but as the RFSS drops quite fast with the distance it might not meet the need.

What are the distances you have in mind?

There are a lot of little OOK (On/Off keying) radios out there that are very cheap, (like $5.00 for transmitter and receiver combined).

The transmitter just transmits a sine wave (in one of the public unlicensed bands), and the receiver asserts a high value when signal is detected. I am using a pair of these, and I get very good signal reception over a range of about 40 feet, through three interior house walls. Line-of-sight, I would bet at least 100 feet. When choosing, lower frequency provides better range.

The ones I found (EBAY, China) had a 25mw transmitter and a receiver sensitivity of -115 dBm, (433 Mhz) which is quite good and should provide maybe 200 feet line-of-sight. The receiver and transmitter combined would fit on one postage stamp.

I would suggest picking up a pair of these, and experimenting. If you put a digitally controlled resistor (see e.g., CAT5111) in the antenna input path, you probably could do a reasonable estimate of RSSI.

I'd like to know how this works, if you try it. Good luck.

John Doner

Broadcast at three power levels. Send a code to be picked up on the receiver. If it picks up one, you are at the farthest distance, two, getting closer, three, very close.

bushn:
I am looking to build a treasure hunt system where people wear a little receiver on the arm which starts beeping when you get close to the object / turn yellow. As you get closer, the beeping get's faster or the colour changes to red. Could I test RF transmission quality? I don't want to use GPS as that is very expensive!
Thanks

Nick

I think you have been taken in by too many TV shows. That is not how reality works.