current measurement with an external accelerometer.

[Lei]

Hello there,

I know how to measure the current based on Nordic tutorial. However, if I connected an external accelerometer by connecting Vdd and Gnd from nordic ev kit to accelerometer ev board, the current consumption from external accelerometer could not be measured/reflected with ampere meter. I wonder if there are other VDD on nordic 51832 ev board can be used to power external sensor and count the current consumption into current measurement (ampere meter).

Thanks,

-Lei

[Simonr]

Hi

First off, I would suggest using a voltmeter to check if there is any voltage at all when trying to provide power to a device. What voltage range does the accelerometer you're using support?

I assume you're using the nRF52832 DK. Please check out the DK user guide for a good description of all VDD pins on the board.

Best regards,

Simon

[Lei]

Hi Simonr,

Thanks for your reply.

Absolutely. I measured the voltage on VDD. The VDD voltage is about 2.9 V with battery powered. I did it following tutorial (e.g. cut sb9, solder sb11). The external sensor worked well through TWI. I could get all sensor data I wanted.

But I noticed the current measurement with nRF52832 DK didn't count the current consumption from the external sensor . More specifically, I even shorted VDD and GND with a 500 ohm resistor, which supposed to give 5 to 6 mA. I measured the current through 500ohm resistor was about 5.8mA. But from ampere meter with P22, it still showed less than 100uA. I speculated the current measurement introduced in DK guide didn't count current consumption from external sensor. 

BTW, DK manual didn't mentioned details about each VDD on board. I measured them. They were all connected (shorted) together.

I wonder if anyone had similar situation before.

Thanks

-Lei

[Simonr]

Hi

Just to clarify. Your accelerometer works as intended, correct? At first, I thought you were struggling to get it up and running, but it seems like you are only struggling to measure its current consumption, am I right?

The VDD_nRF pin on P22 is only the current to the nRF chip, which explains why you don't see a change in the current when connecting an external accelerometer. To measure the current draw of the accelerometer you should place the ampere-meter in series with the accelerometer to get an exact look at the accelerometer current consumption.

Best regards,

Simon

[Lei]

Everything worked okay. I wanted to evaluate the current consumption for nRF52832 + external sensors. True, I can just measure the current through external sensor and add it into total current consumption. But that's not I originally wanted. Ideally, the current measurement through P22 gives overall current evaluation (e.g. 52832+any external sensor).

So my understanding is that the nRF DK currently cannot measure nRF+external sensor through P22. Is it correct? Just want to clarify.

Thanks,

-Lei

[Simonr]

Lei said:

So my understanding is that the nRF DK currently cannot measure nRF+external sensor through P22. Is it correct?

 That's correct!

Best regards,

Simon