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    BME280: SPI modes and power consumption

    BME280: SPI modes and power consumption

    New Poster

    I have a BME280 connected to a ATtiny85 using SPI. There are 10k pullups because the module I bought can be used in SPI and I2C.

    As I don't have an accurante milliamps meter, I'm powering both using a 5V source via a LED. This gives me 5V - 1,4V = 3,6V. This is borderline, but it's the best I have. By the brightness of the LED, I have a clue about the current consumption.

    So I read the sensor, go to sleep and on wakeup, read again... Everything works except the power consumption during sleep is high.

    When I use SPI mode 00, the LED is always bright with short flickering when reading the sensor.
    When I use SPI mode 11, the led is off and only flashes when reading.

    Is the BME's power consumption different using the different modes?
    I can't find any clues in the datasheet.

    It could very well be that I somehow partially burned the sensor while testing/trying/... (=learning).

    PS I think the excess current goes via the SCK pin.

    2 REPLIES 2

    Community Moderator
    Community Moderator

    @Bert wrote:

    PS I think the excess current goes via the SCK pin.

    This would also be my expectation, due to the fact that SPI modes 00 and 11 have opposit clock polarity (i.e. one will have SCK idle at '0', and the other at '1') and that you mentioned pullups on your module.

    True, but the resistor is a 10k one. So 3.6V / 10k = 0.36mA. I would think this is too little to light a LED.

    I don't know the inner workings of the digital interface of the chip. My guess is that I somehow managed to damage it causing high current on this particular pin.

    I don't know if the high current is also there when the interface is enabled (low CSB). But at least when the interface is in high-z mode, there is excess current on the clock pin.