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CC2540: Converting RSSI results between dBm units and 0-250 scale

Robin Howell
Prodigy 30 points
Part Number: CC2540

Context:

We are using the CC2540 to test BLE signal strength of our products in the UK, it reports RSSI results in dBm units (e.g. -30dBm is strong, -90dBm is weak).

We are also working with a far-east partner that also use the CC2540 to test BLE signal strength of our products. But they report RSSI results in 0-250 scale (0 is minimum strength, 250 is maximum strength). Due to communication issues and personnel changes, they are unable to explain how/why they report RSSI results in 0-250 scale, nor how to convert them into dBm units.

Questions: (I've already checked forums & datasheets and did not find specific answers to these)

  1. Do any of the drivers / firmwares / associated softwares from TI enable CC2540 to switch between dBm units and 0-250 scale?
  2. Is there a TI defined function / algorithm / conversion formula for converting CC2540 results between dBm units and 0-250 scale?

Thanks!

  • 0
    TI__Mastermind 40570 points

    Hi Robin,

    I would suggest using the HCI_readRSSI() function as this HCI command provides the last RSSI measured. With regards to switching between the 0-250 scale and dbm, it seems this was a custom conversion that was done internally by your partner. As far as I am aware, there is no function that returns RSSI in a 0-250 scale or converts it. I would try to find which dbm value corresponds to the 250 value and which value corresponds to the 0 value by performing some txPower testing, this may allow you to derive the conversion formula used. However, I would strongly suggest using the HCI_readRSSI() function if possible.

    Best Regards,

    Jan

  • 0 in reply to Jan
    Prodigy 30 points

    Thanks Jan

    I will try to confirm if our partner has implemented a custom conversion, then get them to switch to using the HCI_readRSSI() function. I'll report back on my findings to either close out or continue this thread

    Regards

    Robin

  • 0 in reply to Robin Howell
    TI__Mastermind 40570 points

    Hi Robin,

    Sounds good! I will close this thread in the meantime, once you have an update please reply to this message and it should open the thread back up.

    Best Regards,

    Jan