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Reduce range to less than 5 cm

Naresh Gupta
Prodigy 150 points
Other Parts Discussed in Thread: CC2541, BLE-STACK

Hi,

   I'm creating an application that will exchange data between two CC2541 devices over very short distances, say in the range of 5 cm or lesser.

  Is there a way to reduce the range so that only devices closer than 5 cm can see the advertisement packets and initiate a connection ?

Thanks,

Naresh

  • 0
    Intellectual 265 points

    You can look at the RSSI readings at the short distance of 5 cm for your devices. However note the RSSI measure is not very accurate in terms of monitoring for distance as it depends on various environment factors and presence of obstacles, etc. At such a short distance you might be ok to specify a RSSI threshold which the devices would accept. Need to experiment with that a bit to see if it would fit your needs. 

    Regards,

    Raj.

  • 0 in reply to Raj Sarkar
    Prodigy 150 points

    I tried the RSSI readings already using Central+Peripheral sample application but the problem is that these readings are not giving an accurate mapping with respect to distance.

    Is there a method to limit the Tx power while sending the advertisement packets? (For example any registers that set the Tx output power). Ideally what I would like to do is to allow connections at only less than 5 cms, but once the connection is made, I would like to increase the Tx power so that the remaining communication can happen at longer distances also.

    Thanks,

    Naresh

  • 0 in reply to Naresh Gupta
    Prodigy 150 points

    Hi,

       I tried setting the following:

           HCI_EXT_SetTxPowerCmd(LL_EXT_TX_POWER_MINUS_23_DBM)

           HCI_EXT_SetRxGainCmd( HCI_EXT_RX_GAIN_STD );

       Even with this the two devices can communicate (at least) to 3 m.

       Is there some other way to reduce the Tx power?

    Thanks in advance,

    Naresh

  • 0 in reply to Naresh Gupta
    TI__Mastermind 36395 points

    Naresh, 

    Cut the path to the antenna, this will reduce range significantly. You can try it by just removing a couple of series components on you existing hardware.

    Regards,
    /TA

  • 0 in reply to Naresh Gupta
    Prodigy 10 points

    could you please tell me how to setting these following:

    HCI_EXT_SetTxPowerCmd(LL_EXT_TX_POWER_MINUS_23_DBM)

           HCI_EXT_SetRxGainCmd( HCI_EXT_RX_GAIN_STD );

    which tool do i need? Thank you!!!

  • 0 in reply to giang pham van
    TI__Guru** 105180 points
    Hello,

    You are posting to a thread that has been dormant for over 3 years, so we may not have the full context to your inquiry.

    You can call these APIs directly from your application. Note that standard RX gain in the CC254x is the default setting in the BLE-Stack for CC254x BLE.

    Best wishes