Author Topic: Bias mode OLED only shows output to about 70 (in any range) - Raw out is correct  (Read 1620 times)

Raydur

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Hi. I've got a peculiar issue. When the CurrentRanger is in Bias mode, the measurement shown on the OLED is incorrect once it goes above about 70. At that point, the OLED stays near 70 (anywhere between about 65 and 75 with some fluctuation). It shows this regardless of what range is selected (they all show about 70 if the actual value is above that). If I measure it manually on the Raw Out using a DMM, it has the correct value. Please see attached pic showing the discrepancy between what is shown on the OLED vs the DMM. I've tried this on 3 different CurrentRanger units (all shipped in the last few months), and the behavior is consistent. The CurrentRanger is powered from a LiPo battery and no USB is connected. This occurs whether the test circuit is powered from a battery or from a DC supply. Test circuit supply voltage is 3.3VDC. If I disable bias mode it seems to work as expected (for positive voltage).

The reason I am operating in bias mode with a DC source is because there are capacitors on the test circuit and the current could be both positive or negative depending on whether the source voltage is higher or lower than the state of charge on the capacitors.

Have I found an issue or am I doing something wrong?

Thank you.

Felix

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Thanks for posting this. I think you have just found a bug, I can replicate on a known good unit.
May have been introduced when I added split supply ADC referencing.
I will have to look into it and come up with a fix, should be pretty straight forward, hopefully I have an update in the coming days.

Felix

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I made a new release v1.1.1, this should fix the bug you reported and add a few more other changes. See this commit for details.
There is also a v1.1.1 .uf2 available so you can just reflash your CR with it. Please ensure you write down the startup calibration values, or better - just backup the old current.uf2 file from the CR before you overwrite it with the latest version. The update procedure is described in the guide.

Raydur

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Hi Felix,

Possible new bug with the new units/firmware - I hooked up a 46uA resistive load (3.4VDC, 74k) and it reads fine without BIAS enabled. As soon as I enable BIAS mode it locks up and restarts. I've tried 3 of the new units/FW and all behave the same. The unit doesn't lock up until I connect the load (or enable BIAS if it was already connected).

Regards

Felix

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Hi Raydur,
Thanks for reporting this, indeed there is a lockup+restart in firmware 1.1.1 when you apply more than a few uA LOAD in BIAS mode.
This looks to be a firmware issue and not hardware related, since it's not present in previous firmware 1.0.0.
I am investigating and looking for a fix.
Thanks for your patience.

Felix

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I released v1.1.2, this should take care of the latest issue you reported above.
You can update the firmware from the latest .uf2 file in that repository. Please ensure you write down the startup calibration values, or better - just backup the old current.uf2 file from the CR before you overwrite it with the latest version. The update procedure is described in the guide.

Raydur

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Hi Felix.

I'm having a bit of trouble getting the firmware updated with the .uf2 file. I double tap the reset button and can get to the bootloader and CURRENT.uf2 file. I then replace the CURRENT.UF2 file with the new uf2, but I'm not sure what I'm supposed to be doing at that point to get it to use the new file. I've tried the reset button and just powering it off/on. The guide is indicating this is just drag and drop, so I'm sure it's something simple but I'm just not getting it to work. When I power the unit back on it is still showing 1.1.1.

Am I missing a step?

Thanks

Felix

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Sounds like it is not accepting the uf2. Which means there will be a very quick blinking activity and it will stay in bootloader.

Make sure you download the whole Github repository as a ZIP file, otherwise github can remove \r characters.
After you get the ZIP, unpack and get the uf2 that way.

A successful uf2 firmware update automatically resets the board and starts the new firmware without any required action from the user.

Raydur

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That worked! Thanks, Felix!