Vme290 v0.3.2 schematic?

[tiltec25]

I’m working with the VME290 and am having issues reading the battery voltage properly. Interestingly, I can find schematics for the VME290 v0.3.1 board, but not the v0.3.2 - anybody found one of those and can tell me if he power circuit and vbat reading has changed.

This looks like the currently shipping version from amzon, e.g., https://www.amazon.com/dp/B0D9JWT4P1?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

The main difference to previous versions is that the buttons are white and are pointing to the back instead of black and pointing out from the long side.

Documents that I did find are here: https://resource.heltec.cn/download/HT-VME290

[bns]

How do you infer that your board is v0.3.2?
Also, the link you shared shows the buttons point out from the long side, which matches with the VME290 that I have.

Regarding the battery monitoring: I hope to check this out later today when I am back home, and will report in the appropriate topic Analog Batt read in Vision Master E290 2.90 E-ink - at least for the version that I have, and I am not sure whether there are indeed different versions out there.

[toddnz]

I do have both versions of the board here, and the battery monitoring does seems to work the same.

[tiltec25]

Great - thanks for the replies. I get more reproducible results now after switching to different batteries (the ones I tried before have some circuitry in near the LiPoly cell - not sure what that does).

When I switch a partially charged battery from one board to another, the voltage reading comes along properly now.

Still slightly confused, since when I put a voltmeter on the 4th pin from the top of J2 it should be the vbat pin 7 - but even with full bat I read 3.3V instead of the 4.13V I get on the battery terminals. Attaching a couple of photos that show the v0.3.2 board. The J2 connector has pin 12 on the fourth pin from the top - so still slightly confused about the schematic.

[tiltec25]

[tiltec25]

@bns - here is a closeup of the buttons on my board.

[bns]

@richard3366 or @ashley can you please clear up on the version numbering in the downloads folder? And can the appropriate schematic for 0.3.2 be made available? Because it doesn’t match with the unnumbered 0.3 doc and also isn’t 0.3.1 given this silkscreen.

[toddnz]

Oh, you’re right, it does look like the pinout of the header changed… I suspect that VBat is probably still connected to GPIO7 internally though, and that it’s just no longer broken out on the header(?)

I’ve heard that ESP32’s ADC readings can be quite imprecise. I think(?) the ESP32 variant used on VM-E290 does actually have a factory calibration burned into it, which you can use to compensate the readings. Have you experimented with this?

It might not be necessary, but I believe you can also adjust the attenuation to place your expected voltage right in the middle of the ADC’s accuracy sweet-spot.

https://docs.espressif.com/projects/esp-idf/en/v4.1.1/api-reference/peripherals/adc.html#application-example

[tiltec25]

Thanks @toddnz - yes, VBAT is still on GPIO7 and by reading the ADC repeatedly and putting it into a better precision range by adjusting the attenuation works ok.

I’ll have to look at the factory calibration you’re referring to - not urgently, as for now I just needed a coarse vbat value.