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BOOSTXL-CC1120-90: Interference when using 2 pairs of CC112-90 coming in each others range

Arun Raj
Prodigy 30 points
Part Number: BOOSTXL-CC1120-90
Other Parts Discussed in Thread: CC1190, CC1120

Tool/software:

Dear TI,

We are using combination of CC1120-90 in a weighbridge project, where we are connecting a Master device to a Digital Load Cell(10 Nos) wirelessly with one pair of radios, In this system Master Device polls the Load cells every 40ms and reads the Load cells and read the values in case of any loads on the weigh bridge... Another pair of radios are used to send the measured Load cell/ weigh bridge value from the Master device to a seven segment Display Unit, These values are send to the Display Unit every 1000ms approximately.. All radios were configured to work at 868MHz, 50Kbps, 2-GFSK modulation, We have implemented Address Filtering feature in these radios and tested, which seems to work fine. In this scenario when the radios communicating between the Master and Load cells are enabled, the system seems to work fine with few misses/errors... but when the radio between the Master and the Display Unit is turned on simultaneously the misses/errors seemed to increase exponentially and the system fails to read the Load cells correctly...
To mitigate this issue we changed radio's (connecting the Master device to Display) settings to 200Kbps bit rate and 4-GFSK modulation, keeping the setting of the other radios as default 50Kbps, 2-GFSK. We observed that the system is now reading the load cells properly (with still few misses/errors) and the Display Unit also is working as intended. Thus we are somewhat certain that the errors were caused due to interference of the nearby radios.
We would like to understand if this is something we should expect in this scenario, can you please suggest us methods that we should adapt to reduce error due to interference of nearby radios.

  • 0
    TI__Expert 4860 points

    Hi Arun,

    From your description, I think the issue is that the master is both trying to transmit to the display unit with one radio and at the same time receive from the load cell unit with another radio. Because both radios on the master device seem to be very close, the Tx radio interfering the Rx radio is expected, especially if they are on the same frequency.

    Changing to 200 kbps on the master device to display probably reduced the errors because the transmission are shorter. To be sure of this I would need to see some kind of traces that show when each radio is in Tx, Rx, or off.

    My recommendation would be to synchronize the radios so that the master can't be transmitting at the same time that it is receiving on the other radio.

  • 0 in reply to Diego P
    Prodigy 30 points

    Dear Diego,

    Thanks for your reply
    As mentioned in the forum, there are 2 pairs communicating as shown in the attached picture.
    When pair one alone is operating the system is working as expected. When pair 2 is turned on , there is a lot of package losses on pair 1.
    1. Can we isolate pair 1 from pair 2
    2. Can we maintain pair 1 and pair 2 in two different channels so that no inteference can occur
  • 0 in reply to Arun Raj
    TI__Expert 4860 points

    How close are unit 1 and 3 on the master? Are they on the same PCB?

  • 0 in reply to Diego P
    Prodigy 30 points

    They are on different PCBs and are kept around 10 cm apart

    Is there any constraints on this?

  • 0 in reply to Arun Raj
    TI__Expert 4860 points

    Being only 10 cm apart when one unit transmits the other device will pick up a relatively high signal especially with the CC1190 and it is blocking the other unit from receiving from one of the other 2 units.

    You can try using different frequencies, but may still have interference issues because unit 1 and 3 are physically very close. If you do this you should choose frequencies that are 10s of MHz separated.

    Another option is to synchronize unit 1 and 3 so that when one needs to transmit or receive the other unit doesn't transmit.

    Finally you can also use the carrier sense functionality of the CC1120 to check if there is a device transmitting on the channel or not.