Need to get RSSI (~range) output of a module (< $ than XBEE)

Wireless & IoT
1

I would like to know when two transceiver modules are within a given, nominal distance, to within some arbitrary accuracy. Distance may be 10-50ft, say. There may be multiple nodes, so I need to associate the RSSI with certain address (s) .

I’ve been playing with the XBEEs, and it looks like I can make those work. I’m also looking at the Nordic modules. With the Nordic’s, I’m not sure I can observe the RSSI. With the XBEE’s, this is possible via a PWM output or a digital message in the API layer. The Nordic module is about 1/4 of the cost of the XBEE.

Are there any other FCC approved transceivers that may give some kind of representation of range, which are significantly cheaper than the XBEE’s?

One possibility is turning the transceivers power down to some value (possible with the Nordics) and then yield a binary representation of range. The Nordic’s can do this, but I’m not sure if one of the settings would meet my spec.

2

I think that the TI transceiver chips have RSSI, unlike the Nordic ones. They are harder to use, though.

3

Some experimentation should reveal that the RSSI value is useless as a general range indicator. This is because the value depends very strongly on the relative orientation of the transmitter and receiver antennas and the presence or absence of nearby surfaces that absorb or reflect radio waves, as well as the distance between the receiver and transmitter. However, in certain carefully defined setups, you might be able to make use of RSSI values to determine distances.

Pololu sells a cheap, C-programmable module (Wixel) based on the TI radio chips that is great for experimentation on various related topics.

4

jremington:
Some experimentation should reveal that the RSSI value is useless as a general range indicator.

I would tend to agree. However in this case, I am needing more of a qualitative assessment of range. These modules will be attached to humans, and they add sort of a natural dithering which actually help the situation. Add to that the fact that you have the redundancy of two units, each with their own RSSI (observation of range), and it is looking like I might have a chance. I will hopefully be testing the first implementation of my filter later today.

Thanks for the heads up on the TI chips, I will be trying to track those down.