In the midst of the Corona Pandemic we are looking to develop a wearable sensor that when within approximately 2m of another (of the same type) of wearable sensor will log an event.
The ideal would be a low cost and very low power. It must work without line of sight since the sensor can be in your pocket etc. I've looked at all sorts of proximity sensors and none seem to be able to do the job.
My only solution I could come up with is a sub Ghz RF transceiver that polls (twice every second) and is in receive mode for the rest of the time and when a message is received an ACK is sent. The output power will be set very low (0 dbm) without an antenna so should get around 1.5 to 2.5 m range irrespective of a human body that is in between sender and receiver (If I go with my intuition).
Problem is that lowest RX current is around 7mA which means on a 1000mA battery will last less than a week.
Has any body done anything similar or have any advise on maybe another type of technology I can use?
Location is not important and it is most likely going to be indoor.
Any advise will be highly appreciated
Best Answer
I once designed a non contact telephone line tracer. The specification was to be able to detect a 1Vpp 1kHz sinusoid signal on a 1 metre length of wire at a distance of 1 metre. The input was a probe tip connected to a static protected FET opamp with a high Q filter. I imagine a 2 metre range could be achieved by pushing the voltage up to about 9V.
The method I used was essentially an electrostatic pickup. A homemade near field RFID type thing might work as well. Hi Q Coil being fed at (say) 100kHz, with a simply LC being used as pickup. Similar to resonant power transfer.