# Using the RSSI value from BLE HM-10 to measure distance

Hi ,

I'm currently working measuring the distance in 1dimention from the RSSI value I obtain from the HM10 BLE module ( Basically converting from RSSI to meters ).

After some research , I found out that this equation is the way to go :

d = 10 ^ ((txPower-Rssi) / 10n) , where n ranges from 2 to 4

I tried finding out the value of Tx and based on data I'm receiving , the measured power is C5 which is 197 in decimal .

I looked into the data sheet for the HM-10 module to find out what value C5 means but I didn't find anything I also looked at the operating power for the BLE module and it was 0 dBm which is 1mW

so the main 3 questions for anyone who used the RSSI to measure distance or has an idea how to do this are :

1. what is the txPower in this case ? is 1mW ? or is it mapping 0.01-5mw(which is the possible operating power for the ble) to 0-255 ? or is it something else ?

2. what is the value of n for this module ?

3. is there another equation that would result in a better result ?

an answer for any question would really help I already have an idea on how to do Trilateration but I just want to get the main conversion done first

Thanks in advance RSSI measurements are more or less useless for distance measurements.

Antenna orientation and the presence of nearby reflecting and absorbing surfaces have a much stronger influence on RSSI than does distance.

I know but for this specific case I can only use BLE for distance measurement and the value that I found possible to do this is the RSSI

Let us know how well it works.

and the value that I found possible to do this is the RSSI

No. You found a value that you think varies with distance. While it does, there are other factors that have much more influence over RSSI than does distance.

If measuring distance based on RSSI was really practical, don't you think you'd see it being used in more places?

Each receiver's RSSI circuit has to be calibrated as a function of distance at some TX reference power output and antenna type. Also, the path has to be free of reflections from both ground and vertical objects. There are just too many factors that make this method unreliable. For these reasons, it is seldom used in any serious locator technique.