Heavy calculation could make battery life shorter?

[benevbright]

Hi,

I'm making device with nrf51822 chip and 400mA battery. It connects to smart phone. It has to calculate heart rate and some other things, so it's doing it on device side(it has to do work without connection with smart phone sometimes) and I think amount of calculation is not that small.

So, now I wonder how much complexity of calculation effects to battery life.

how many times difference between heavy calculation and idle process for battery life?

I just wanna know roughly, so that I could change plan to better plan.

and PLUS How does Fitbit have such a long battery life?

Thanks.

[Susheel Nuguru]

Its not about heavy calculation, its about how long those calculations are keeping the CPU active. Heavy calculations are not different than any other CPU instructions (as nRF51 does not have FPU) If the calculations are keeping the CPU active half of the time that is heavy draining of battery. I have tried beacon module to keep active all the time to see how fast it drains the battery and keeping the CPU 100% active drained a lithium coin cell in 5-7 hours.

[benevbright]

Oh great help. Thanks. Then is there any way to make cpu inactive by firmware code? sleep(XXXX) makes cpu inactive?

Thanks for help.

[benevbright]

How about fitbit? to calculate steps, I think they should keep device's cpu active all the time but their battery life is so long. OK maybe not all the time. when it detects that user walks.

[Susheel Nuguru]

fitbits does BLE communication like any other low power gadget. I am not expert in their operation, but i would think that they make the cpu go to sleep majority of the time and let all the calculations in the application inside the peer device(phone or other gadget with more battery power). The basic idea of BLE is to transmit as little as possible (and sleep immediately) to the device with more battery and allow it to make calculations.