Why would I get two different current readings from two different PCs using the same PPKII, circuit, and supply voltage?

[rjh]

Hello,

I was measuring the current of a circuit I made using a PPK II and noticed I am getting two different readings from the two PCs I used (a work and a home PC).

Both PCs have the same settings in the nRF Connect software and I am using the exact same circuit and LiPo battery to power it but my average current draw using the work PC is ~1.20mA and my home PC reads ~0.95mA. 

My home PC is much faster than my work one, would that cause a disparity in the readings?

Thanks.

[Håkon Alseth]

Hi,

 

LiPo battery to power it but my average current draw using the work PC is ~1.20mA and my home PC reads ~0.95mA. 

Was the battery charged fully in both scenarios? 

 

noticed I am getting two different readings from the two PCs I used (a work and a home PC).

 Is any of these computers an AMD build? AMD has had usb connectivity issues recently: https://www.tomshardware.com/news/amd-suggest-possible-fixes-for-usb-connectivity-issues

Also, make sure that you try to connect the usb directly to your PC (also; change usb cable if you're getting instabilities)

 

Kind regards,

Håkon

[rjh]

Hi Håkon,

Håkon Alseth said:

Was the battery charged fully in both scenarios? 

Yes, a brand new and fully charged LiPo with the same voltage level in both scenarios. The tests are very brief (<3min) so there isn't any noticeable battery degradation.

Håkon Alseth said:

 Is any of these computers an AMD build?

No, both have Intel processors. One is i9 and one is i7.

Håkon Alseth said:

Also, make sure that you try to connect the usb directly to your PC (also; change usb cable if you're getting instabilities)

I have the USB connected from the PC to the USB Data/Power port of the PPKII if that is what you mean (no USB extensions)? I have used two different USB cables and was able to get the ~0.95mA reading. I have not tried two cables with the PC giving me the ~1.2mA reading; will try today. 

[Håkon Alseth]

Hi,

 

rjh said:

I have the USB connected from the PC to the USB Data/Power port of the PPKII if that is what you mean (no USB extensions)? I have used two different USB cables and was able to get the ~0.95mA reading. I have not tried two cables with the PC giving me the ~1.2mA reading; will try today. 

I meant if you're connected through a usb hub, or directly connected to your computer.

If you have one specific cable that gives a higher reading, it might be that this cable is marginal, thus; the ppk might be missing samples.

 

Kind regards,

Håkon

[rjh]

No hub, direct to computer.

Tried multiple cables on the PC giving me the high readings and still get the same high readings. 

Any other ideas? Would it be helpful to post the graphs from the data logger from the two PCs?

[Håkon Alseth]

Hi,

 

It's hard to say what it can be, if it comes from the board itself or from the measurement.

Is the reading itself correct? Ie. have you tried to measure with a multimeter and see if the reading match with what PPK2 measured?

 

Kind regards,

Håkon

[rjh]

I believe the multimeter I have only goes up to a few μA and isn't very accurate, so of no use for this application. That was the reason I purchased/used the PPKII... to measure current readings in a wider range more accurately.

I looked more into the graphs that nRF Connect Power Profiler output and I did notice that the work PC's period was 11.67s consistently and the home PC's period was 18.56s consistently. That ~7s increase would explain why the average power draw is brought down (the graph spikes, decreases, and levels off) but if the test circuit, usb cable, power supply, and settings are all the same, what would be changing the time period between the two PCs?

[Håkon Alseth]

Hi,

 

rjh said:

I looked more into the graphs that nRF Connect Power Profiler output and I did notice that the work PC's period was 11.67s consistently and the home PC's period was 18.56s consistently.

This is an indication that the PC that is "off" is missing several samples from the usb bus. Which one is sampling incorrect? We have seen in the past that the one that samples slower is the one missing packets:

https://github.com/NordicSemiconductor/pc-nrfconnect-ppk/issues/141

The above issue is highly likely linked to recent AMD usb connectivity issues.

 

Try different ports (2.0 and 3.0), and see if your BIOS/chipset drivers are up to date.

 

Kind regards,

Håkon