nRF52832 SAADC and small batteries

[PW]

Hello. 

I try to make audio noise meter on nRF52832. I used analog MEMS MIC with OPA which I turn on via MOSFET while before measurement. I'm using SAADC triggering by RTC and I take samples by about 25ms. Almost everything works fine. When I'm powering up device from LDO or large battery (CR14250), results are correct, but when I try to power up by two CR2430, device works not very well. Results are clearly to high. I tried to correct situation by couple of ceramic capacitors, but it wasn't helpful. I wonder if it possible to use SAADC in longer measurements (several dozen ms) when we use batteries like CR2430? Maybe better solution will be PDM mic? I wanna to do it on possibly the smallest batteries, eg. CR2450.

Best regards, 

PW

[awneil]

PW said:

I tried to correct situation by couple of ceramic capacitors, but it wasn't helpful.

As AmbystomaLabs asked, what values did you use?

Just randomly slapping on capacitors is not a very scientific approach!

You really need to use an oscilloscope to see what's happening to your supply voltage: if it is sagging, you need to fix that; if it isn't, then you need to look elsewhere for the problem.

Use your scope or a current profiler or similar to measure  your supply current...

[PW]

It wasn't randomly, I was increasing capacitance. I started with 22uF, finished with 3x47uF (X5R). Peaks during measurement decreased a bit, but it was still about 5mA/20ms. Much more efective is to decrease sampling, but I didn't finished that part. I'll back to this on Monday.