Author: Brett Stoddard

Hello all, today the RFID team figured out how to use the Cottonwood to communicate with the Dogbone tags. To celebrate, we measured the Dogbone tag’s RSSI value in wet and dry conditions. This was done to see if RSSI value could be used as an indicator of moist conditions.

RSSI value is a measurement of received signal strength. It’s an acronym for “received signal strength indicator”. It’s often used in WIFI signals. Here is a good article from MetaGeek that explains it further: http://www.metageek.com/training/resources/understanding-rssi.html

For this test, we read multiple RSSI values when the tag was dry first. We then wet a piece of paper behind the tag and recorded the RSSI values again. The picture below shows our setup. It should be noted that while wetting the tag we might have disturbed the system which would mean that our results will need to be backed up with further, more precise testing.

To receive the RSSI data, we sent an “Inventory Command with RSSI” command from the Arduino to the Cottonwood. The command was sent as a character array { 0x44 , 0x03 , 0x01 } and was taken from the Cottonwood’s datasheet. We got back a message that contained the RSSI value in the third byte of the response. Below is a table with the RSSI values measured in wet and dry conditions.

In conclusion, there might be a slight correlation with moisture, but further testing is needed. Also, the distance between the antenna and tag is a large factor in the RSSI value and should be taken into consideration before implementation.