Need to Build Two Circuits That Sense Proximity To Eachother

[marineman78]

Need to Build Two Circuits That "Sense" Proximity To Eachother

Hi all,

I am trying to build two circuits as part of an experiment that can "sense" proximity to one another. So basically, as they the two circuits get physically closer to each other (starting at a range of maybe 10-20ft), an output voltage increases in each of the units which I could then measure or connect to a small speaker. So the closer they get, the higher the voltage. Thoughts that come to mind are RFID, Bluetooth, etc. but I'd be interested in any ideas you guys have.

I also don't have a $100 to spend on this so it'd need to be relatively low cost. Thanks in advance!

-MM

 

[Mike_In_Plano]

Most receiver chips have an RFSS (RF signal strength) line that can give an idea of the signal level coming in.
Unfortunately, any RF technology you use has the weakness of being orientation sensitive. The angle of the antennas or coils will influence the reading greatly.
However, with three coils or antennas used during receiving, you can work out the vector sum of the input and get away from this weakness.
I think (not certain) that Microchip has an RFID chip used for vehicle key locks that has this three coil arrangement.

Best of Luck

- Mike