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CC2640 BLE Module with LMT85 temperature sensor

Other Parts Discussed in Thread: CC2640, LMT85, SMARTRF06EBK


We are planning to use LMT85 temperature sensor with CC2640 BLE Module for our BLE Beacon project.

We want temperature sensor to be on when beacon will transmit which we have set time of 1s(Advertising interval 1s ) otherwise we don't want to on temperature sensor.

Is there any way to turn off temp. sensor when not in use and when beacon will advertise then it will wake.

The other question can this sensor be able to take correct reading(Ambient temperature reading) in short span of time when it awake.

Can we able to power, temperature sensor through GPIO.Can this will effect our system.

I have asked this question to BLE low energy community and they have referred to sensor community for more details.

  • Hi Jasbeer,

    One solution is tying the VDD connections to a GPIO on the CC2640. The CC2640's GPIO pins can supply a max current of 8mA and the LMT85 will pull a maximum of 9uA so you should be fine. This way you can power the LMT85 through a GPIO pin and set the output to high impedance to turn it off when you are not using it.

    The start up time of the LMT85 from applying power to seeing a stable output is 0.7ms (typical) and 1.9ms (max) with a 0 to 1100pF load on the output pin. This will meet your 1s spec.

    Let me know if you have any other questions.

    -Michael Wong
  • Hi
    Thanks for response ,this was very helpful for us.
    Now we have changed our interval to 1 hour i.e our temperature sensor will wake in 1 hour through GPIO and it will wake for 5ms.
    Can anybody tell how much current it will consume.Is it will consume 9uA(taking max. for calculation) for every 1 ms.
    We have to do battery life analysis with swara478 considering temperature sensure consumption also.
    What should I have to edit in swara478 calculation sheet for including temperature sensor.
  • Hi Jasbeer,

    The SWRA478 is only for the BLE power estimation. I suggest you prototype your system on the CC2650DK (SmartRF06EBK) and take actual power measurements as prescribed in the app note. Note that it looks like you're going to be running the CM3 MPU very infrequently, so the bulk of the energy is going to be consumed with the BLE Advertisements.

    Best wishes