calculate current

RE: calculate current

Bjørn Kvaale — Thu, 12 Oct 2017 11:07:54 GMT

These two blogposts (1 & 2) might also help a bit.

RE: calculate current

Bjørn Kvaale — Thu, 12 Oct 2017 11:06:39 GMT

Communication over I2C requires CPU or DMA and the HFCLK (high frequency clock) in order to operate. So you will need to add CPU or DMA current calculations + the HFCLK current consumption. In practice, the average run current for I2C communication is around 1.2 mA. This would lead to around 864 mAh, which is unfortunately more than a coin cell capacity. I would double check this once you get your PPK, but you might unfortunately need to buy a Li-Po battery (or another higher capacity battery) to let it run for >= 30 days straight. This blogpost might help to lower current consumption on I2C bus.

I would also take a look at these two cases if I were you: case 1 & case 2. Case #1 is slightly similar to your query & in case #2, endnode says that from his experience, theoretical calculations can often vary quite drastically with the actual values.

RE: calculate current

Kristian Hansen — Mon, 09 Oct 2017 14:06:07 GMT

Hi, thank you for your reply. Yes, I think a coin cell should be enough for the nRF. I still haven't received my devkit so I can't do any measurements yet, therefore am I trying to do a calculation I can work with for now. I'm asking mainly if there is any big calculations I might have missed that could change the consumption by a lot.

RE: calculate current

Bjørn Kvaale — Mon, 09 Oct 2017 13:32:43 GMT

But given you're usecase, I'm pretty sure a coin cell battery should work. This is again assuming the current estimates are quite correct. You could also consider using a multimeter or buying a power profiling kit to more accurately measure the current.

RE: calculate current

Bjørn Kvaale — Mon, 09 Oct 2017 13:29:59 GMT

Hi Kristian, I am a bit uncertain what your question is. I guess you are wondering if a coin cell battery would be enough to power the nrf52840 for >= 30 days? Is that correct? Considering coin cell batteries can have a capacity of roughly 225 mAh (see this great blogpost), one coin cell battery would last roughly 3214 hours before it would need to be switched out (i.e. 225 mAh/0.070 mA avg total consumption). That is more than the 720 hours in one month. So basically, if your consumption estimates are accurate, you should easily be able to use the nrf52840 for >= 30 days! Worst case, you could consider attaching a Li-Po battery to the nrf52840 (see infocenter).