Difficulty determining current consumption with oscilloscope

[ericoneill]

Hi, I'm currently trying to determine the power consumption of my nrf51DK during different states of my program using an oscilloscope. To do so, I am using an external power supply in series with a resistor on the external power supply pins, and then using an oscilloscope to measure the voltage across the resistor. Here is a picture of my setup:

Regardless of whether I turn on Bluetooth advertising or not or use the ADC or not, the voltage on the oscilloscope looks like the following picture

I am not sure why there is a periodic signal with a period of ~2ms, despite there being nothing in the code that executes at that frequency (That I set up, at least). Is there any issue of the way I am trying to measure power?

Any help would be greatly appreciated! Thanks

[Marco-Luis]

Hi, just two questions:

• What's is the value of the shunt resistor (should be a very low value)?
• Have you measured the Power Supply ripple without the nRF module?

In any case, I'm not sure if this suggestion can be useful to you, but I have read somewhere about placing two capacitors (10uF electrolytic and 0.1uF ceramic) near the nRF module can help smoothing the power ripple.

Just my two cents.

[awneil]

It looks like your series resistor is way too large!