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HDC2080: HDC2080 sampling time

SONU GOYAL
Intellectual 530 points
Part Number: HDC2080

Hi,

We are working on a battery operated device in which we are planning to use HDC2080 temperature sensor with CC2642 BLE IC. We want to take temperature reading after one minute and after taking reading we have to keep it power off to save battery. In datasheet of HDC2080, response time is given as 8 seconds and additional conversion time.

Does this mean we need to keep HDC20280 keep power ON for more than 8 seconds ( response + conversion time ) ?

Please confirm for how much time we should keep temperature sensor power ON for taking one sample reading of temperature.

  • 0
    TI__Guru* 91206 points

    Dear Sonu - 

    You can have the HDC2080 wake your CC2642 up at the interval you decide (based on the available choices in the 0x0E register of the HDC2080). The one minute interval would be, with the interrupt enabled and set to active high: 00100110 or 0x56, also don't forget to write 0x07 register with 0x80 to make the interrupt fire on data ready. 

    Here also are some TI Reference Designs that may be of interest: 

    http://www.ti.com/tool/TIDA-01477

    http://www.ti.com/tool/TIDA-01518

  • 0 in reply to Josh Wyatt
    Intellectual 530 points

    Hi,

    I did not need to wake up the BLE IC. My question is different.

    I want to confirm for how much time I need to power ON HDC2080 to take reading from sensor. I want to keep sensor power off after taking temperature and humidity readings. 

    In our application, sensor will be powered ON/OFF through BLE IC GPIO to save battery. So when I will take reading from sensor I will keep it power ON and after taking temperature reading sensor will get power off.

    So please confirm the time duration for which we should keep HDC2080 keep power on for getting reading?

  • 0 in reply to Josh Wyatt
    Intellectual 530 points

    Hi,

    I did not need to wake up the BLE IC. My question is different.

    I want to confirm for how much time I need to power ON HDC2080 to take reading from sensor. I want to keep sensor power off after taking temperature and humidity readings. 

    In our application, sensor will be powered ON/OFF through BLE IC GPIO to save battery. So when I will take reading from sensor I will keep it power ON and after taking temperature reading sensor will get power off.

    So please confirm the time duration for which we should keep HDC2080 keep power on for getting reading?

  • 0 in reply to SONU GOYAL
    TI__Guru* 91206 points

    Dear Sonu - 

    The HDC2080 needs at least 3mSec after power up to be ready for a measurement. 

    For clarification, the CC2642 MCU consumes ~3.4mA in active mode, no radio. The HDC2080 consumes ~50nA when in sleep mode (state it would be in, in between measurements), so I think you are not saving much battery capacity by turning off the power to the sensor as compared to putting the CC2642 in standby (where it draws ~1uA) and waking it up with the sensor. Totally your choice here - just trying to point out what i think is best power savings approach. You may also benefit from putting the CC2642 in shutdown after defining an I/O pin to wake from shutdown. 

     

  • 0 in reply to Josh Wyatt
    Intellectual 530 points

    Hi,

    My device use case is:

    BLE IC will advertise after 1 minute interval and HDC2080 will take reading after 10 minutes. So HDC2080 will be in shutdown mode after taking reading but BLE IC will keep on advertising after one minute interval.

    So I do not need to wake up BLE IC from HDC2080 interrupt.

    As mentioned HDC2080 needs atleast 3mSec to get reading, please let me know what will be maximum time for HDC2080 to take reading.

    I am doing battery capacity calculation so we need this time required to take temperature reading.

  • 0 in reply to Josh Wyatt
    Intellectual 530 points

    Hi,

    My device use case is:

    BLE IC will advertise after 1 minute interval and HDC2080 will take reading after 10 minutes. So HDC2080 will be in shutdown mode after taking reading but BLE IC will keep on advertising after one minute interval.

    So I do not need to wake up BLE IC from HDC2080 interrupt.

    As mentioned HDC2080 needs atleast 3mSec to get reading, please let me know what will be maximum time for HDC2080 to take reading.

    I am doing battery capacity calculation so we need this time required to take temperature reading.

  • 0 in reply to SONU GOYAL
    TI__Guru* 91206 points

    Dear Sonu - 

    Datasheet, page 5 contains the  typical length of time it will take, based on resolution, as I stated in first post. 

    http://www.ti.com/lit/ds/symlink/hdc2080.pdf 

  • 0 in reply to Josh Wyatt
    Intellectual 530 points

    Hi,

    Thanks for your reply. We will use 14-bit resolution.

    In datasheet, conversion time is given as 8 seconds. Please let me know what is the use of this conversion time.

    Does this mean, we need add conversion time + 610 uSec ( TEMPct)  for this. Do I need to keep sensor power on for atleast 8 seconds to get reading.

  • 0 in reply to SONU GOYAL
    TI__Guru* 91206 points

    Dear Sonu -

    The conversion time for 14 bit resolution is typically 660uSec for %RH and 610uSec for temp. This is listed in datasheet as conversion time and is on page 5 of the datasheet. 

    If you add these together, you will get typically 1270uSec of conversion time for both measurements to be made. 

    here is what that looks like in action - click on image to make larger

    what you see here is start conversion command for 14 bit, interrupt fires around 1235uSec later, we read 0x04 register to confirm data is ready, then read out temp and %RH values. 

  • 0 in reply to Josh Wyatt
    Intellectual 530 points

    Hi Josh,

    Thanks for your input.

    I understood this timing 1270uSec. 

    Please confirm what is meant by conversion time 8 seconds as given in datasheet. Where it will be used?

  • 0 in reply to SONU GOYAL
    TI__Guru* 91206 points

    Dear Sonu -

    The response time (which is what you are referring to, not the conversion time) is the time the %RH sensor polymer needs to get to 63% of the final value after a change in relative humidity, which is independent of whether or not the device is powered. If you are measuring every ten minutes, since humidity normally changes very slowly, you should be fine turning the device on, making a measurement as discussed above and remove power to sensor, loop as mentioned. 

  • 0 in reply to SONU GOYAL
    Intellectual 530 points

    Hi Josh,

    Thanks for confirmation.

    It means I can take 1270 uSec time for battery capacity calculation. We will keep HDC2080 sensor powered on for 1270uSec to get reading.

  • 0 in reply to SONU GOYAL
    TI__Guru* 91206 points

    Dear Sonu - 

    1270uSec is not enough - please include 3mSec after power up and the time it takes to send the conversion command and retrieve the measurement bytes. 

    This would in total (running at 100kHz I2C) be around: >3mSec + ~300uSec + >1270uSec + (300uSec to check register 0x04 if not using INT/DRDY) + ~1mSec to read back registers 0x00 through 0x03) = ~5.87mSec, I would round up to 6mSec for any rough calculations you are making.