Unstable vdd

[etamar]

Hi everyone,

I have a nrf52-DK, I made samples with the saadc unit and i noticed there are unexplained peaks. I connected the MIC's output (its VDD is from the board) to an oscilloscope and saw the peaks occurs when the vdd(provided from a usb cable) has minor fallings.

The circuit is in the picture below:

Here the green graph is Vdd, and is measured 2.97[V], the yellow graph is the microphone's output.

I then connected the MIC to a power generator and with the same input voltage the signal was clear. When i made the coin battary to power the board the voltages in the scope had bigger falldowns, and the MIC's output is worse: and after a few second suddenly everything clears out and everything is good:

Why from a usb it doesn't happen? What can cause this problem?

Thank you!

[Øyvind Karlsen]

How much current does the microphone draw? Possibly it could be too high for the coincell battery to be able to operate.

[etamar]

It is possible, only that with the coin cell it works perfectly, and from a USB it doesn't stabilize. To solve this for now, and to still have a uart connection with the computer I plugged in 2xAA batteries and shorted their negative side with the board's ground, it works good but still..

[Øyvind Karlsen]

Ah, my bad. I saw this as the kit not working when powered by battery, but working when connected to USB. USB noise is quite common, you can try to smooth it out with a large capacitor (µF or so) at the 5V terminal or use a "usb decrapifier" on the USB line.

[etamar]

The capacitor didn't change it : I will stay with the battery for now, if you will have any solution i'll be happy to hear :)