How to calculate tx power using HC-05

I want to calculate tx power of any android device's bluetooth. Can someone suggest some AT commands for this?

google can help you find stuff like this.

I am able to find rssi value, I want to find tx power.

couldnt find any at command , can u help

click the link I provided, it seems to me they mention AT commands

yeah i did, only rssi calculation is described there, using AT commands

RSSI = Received Signal Strength Indication

There is no standardized relationship of any particular physical parameter to the RSSI reading. The 802.11 standard does not define any relationship between RSSI value and power level in milliwatts or decibels referenced to one milliwatt (dBm). Vendors and chipset makers provide their own accuracy, granularity, and range for the actual power (measured as milliwatts or decibels) and their range of RSSI values (from 0 to RSSI maximum).[2]

what are you looking for?

If the android device had a socket between the bluetooth device and its antenna then you would insert a RF power meter and measure it.

Telling from the outside, what TX power the device was using, would be a bit impractical.


The Tx level is the power in decibels per milliwatt (dBm) at which a modem transmits its signal

I actually saw a formula for calculating distance using rssi which involved tx power.

I actually want to calculate it and use it in my code, can AT commands sort this

No, since the HC-05 does not know how far away the other Bluetooth device is or the characteristics of its antenna.

You could in a series of comparisions with a 2.4Ghz transmitter of known power and antenna gain do some comparative field strength measurements. But that would still not provide the TX power of the android device unless you knew the exact performance characteristics of its antenna.

Why do you want to know the TX power of an Android Bluetooth device ?

As mentioned, the HC-05 will only give you the RSSI information and this is an arbitrary number that is vendor dependant.

See this PDF for more information

There are four units of measurement that are all used to represent RF signal strength. These are: mW (milliwatts), dBm (“db”-milliwatts), RSSI (Receive Signal Strength Indicator), and a percentage measurement. All of these measurements are related to each other, some more closely than others. It is possible to convert from one unit to another, albeit with varying degrees of accuracy, and not always in the extremes of the measurement range

I want to calculate distance between hc-05 and any android device using rssi and tx power, I have found rssi and the formula for this, just need the tx power
I have another doubt ,would i need tx power of android or HC-05 in this formula

No you dont.

You need to know the performance characterics of the Bluetooth android devices antenna as mentioned in post #10.

In the UK we are in the middle of a 'pingdemic', with currently over 600,000 people self isolating, caused by the utter folly of those who assumed that acccurate distances can be measured using Bluetooth RSSI measurements between devices such as smartphones.

i understand that these distances are not at all accurate, but that's what my mentor needs me to do
Actually we dont need accurate measurements for our project

also pls answer this

tell your mentor to read this article How Far Can You Go?

so use RSSI as a proxy for distance like "possibly close", "possibly nearby", "possibly far".. and this won't be foolproof at all...

1 Like

thanks and yes our project fits in this, because we dont want exact measurements

Nope, doesn't work, hardly at all. path loss is highly variable depending on relative antenna position, orientation, metal objects in the vicinity, RF-absorbent materials in the path - all that without even considering multipath fading.

To measure distance with RF requires clear line of sight, no multipath and calibrated antennas and cable runs. Its almost impossible in the real world to avoid multipath.

The best you'll be able to do is probably plus or minus an order of magnitude, on average - is this actually useful?

Well, that's a relief because you can be sure you won't be getting any.. You might check a nearby thread about using the STATE pin. This can be used to tell if Bluetooth is connected or not, which may be interpreted as "in range" or "out of range", and there are no ifs, buts, or maybes about it. This may turn out to be something useful, which is more than can be said for this pointless RSSI saga.

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.