Author Topic: Battery Lead Noise [solved]  (Read 374 times)

wile1411

  • Jr. Member
  • **
  • Posts: 53
  • Country: au
Battery Lead Noise [solved]
« on: October 17, 2018, 08:18:21 AM »
I've got my Current Ranger and found that the lipo I'm using has 11cm of battery lead. I'm going to shorten this over the weekend. Just wanted to check if that lead this likely to be the main cause of the output voltage reading I'm seeing at the top left of the OLED jumping all over the place when there is no load? Or would it be mainly the OLED itself?

Without the LPF: in the mA range, it floats around 0 to -2. In the nA range it's between -14 to 25 (ish)
With the LPF: in the mA range, if floats around 0 to -2. In the nA range it's between -5 to 4 (ish)

I've got to buy some male JST connectors to have a detachable connector for the LIPO batteries to test my projects with the CR.
« Last Edit: November 19, 2018, 10:07:49 AM by Felix »

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 5850
  • Country: us
    • LowPowerLab
Re: Battery Lead Noise
« Reply #1 on: October 17, 2018, 12:14:53 PM »
Seems a bit high even with LPF, but in the nA range that could just be noise in general.
You would also want to shorten the inputs to see if that still happens, I would expect not under normal circumstances.
How do you mount your OLED, directly to the header as seen in the guide, or using wiring?

I do test all units for low noise and all that, including with OLED readings and without OLED (scope).

wile1411

  • Jr. Member
  • **
  • Posts: 53
  • Country: au
Re: Battery Lead Noise
« Reply #2 on: October 18, 2018, 10:21:14 AM »
I don't doubt it's probably noise in the area. I'm just struggling to first a way to test that is the case / find an area away from it. I've walked out into the yard and it was about the same. I'll need to cut the battery leads as that's my main suspect at the moment.  The OLED was mounted via the header (No wiring)

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 5850
  • Country: us
    • LowPowerLab
Re: Battery Lead Noise
« Reply #3 on: October 18, 2018, 11:45:52 AM »
One thing to note - when the I2C bus is used, there is more noise coupled on the CR output because of the I2C clock. This is visible on a scope.
But it's assumed you would generally not use the OLED when using a scope.
In any case the OLED is usable even in the nA range which tends to be the most sensitive to picking up noise.

wile1411

  • Jr. Member
  • **
  • Posts: 53
  • Country: au
Re: Battery Lead Noise
« Reply #4 on: October 18, 2018, 11:47:59 AM »
unfortunately, I've not been able to afford a scope for this hobby. I've seen the cheap one of aliexpress, but have hesitated getting those due to quality.

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 5850
  • Country: us
    • LowPowerLab
Re: Battery Lead Noise
« Reply #5 on: October 18, 2018, 12:02:44 PM »
You'd need at least a decent RMS DMM for use with CurrentRanger.
The OLED is certainly not at the same spec of the meter's output. It's more or less a very portable option and usable reading the more averaging is done by the SAMD21's 12bit ADC. The default firmware does "minimal" averaging to limit output noise and still give a usable reading. If your intent is to use it with the OLED exclusively I would ramp up averaging in firmware.

wile1411

  • Jr. Member
  • **
  • Posts: 53
  • Country: au
Re: Battery Lead Noise
« Reply #6 on: October 19, 2018, 03:22:00 AM »
I've got a Fluke 87 RMS DMM

Intent would mainly use it via the bluetooth & DMM while on the workbench. OLED would be used for initial/quick onsite inspections of motes in the field to verify sleep cycles.
Just going through the initial 'do it work / how did I stuff it up' stage. I'll report back once I've shorten the batt leads.

wile1411

  • Jr. Member
  • **
  • Posts: 53
  • Country: au
Re: Battery Lead Noise
« Reply #7 on: November 18, 2018, 04:38:14 AM »
Just to follow up this issue - I updated to the latest firmware and my current ranger is solid now. No flickering between na & ua.
Guess the updated averaging fixed what I was seeing on the DMM.

I also shortened my batt leads as much as possible just in case :)

alexsh1

  • Jr. Member
  • **
  • Posts: 50
  • Country: gb
Re: Battery Lead Noise
« Reply #8 on: November 18, 2018, 01:49:16 PM »
No flickering between na & ua.
Guess the updated averaging fixed what I was seeing on the DMM.

Correct. Due to picking up some noise the autoranging was going nuts before.
Averaging smoothed the output and autoranging became more stable.