Anyone had any luck or solution reading battery voltage via grove shield? https://www.seeedstudio.com/Grove-Shield-for-Seeeduino-XIAO-p-4621.html
I have examined the schematic and it does not seem to include a function to read the battery voltage. The battery terminal voltage must be resistively divided and connected to the XIAO port for AD conversion.
(The battery pad on the back of the XIAO is not connected to this Grove-Shield.)
Have you found anything interesting about this? i am planning on connecting a bare 18650 battery without protection and if what you mention is correct it is not safe…
If you use A0/D0 (GPIO2) to monitor battery voltage, you may not be able to upload your sketch. See the link below for details.
“XIAO ESP32C3, unable to upload sketch or re-write bootloader - #18 by msfujino”
Hi, I hope someone could help me with the problem I encountered. I am using XIAO SP32C3 together with BMP280 sensor in my product. The code and hardware are pretty simple, basically driving two LEDs depending on the pressure. It all worked well, until today I added this code for checking the battery voltage. The battery code works well, but the BMP280 stopped sending the parameters to the serial monitor, and I’m just getting NAN instead. I just added the voltage divider, two 220K resistors as suggested and I also added 3 colored LEDs to the free pins A1, A2 and A3, which wee previously unused, so in fact I haven’t changed anything, just added the above. If I upload previous code without the battery check part, BMP works without problems. So I wanted to ask if there may be some known issue with using both ADC and I2C, or something like that?
I would really like to be able to use the battery check part. I have 150 boards and this XIAO board really has some weird solutions, like almost no indication, charging current of 350mA which is pretty scary considering I’m using LiPo poach battery 150mAh and I’d really prefer if they don’t start exploding once delivered to users, etc. I’ve been using nRF52840, but decided to switch to ESP, frankly mostly because of the price, because any board would do, providing it has a charging capability, and that’s where I haven’t been careful enough. The battery does have some kind of protection circuit, consisting of 8205A and something called G3JS, but I don’t know if that’s sufficient enough, so if anybody knows more, I’d appreciate any help, with this and the problem above.
Cheers,
Miso
Hi Mishko959,
I wrote a proper sketch and tried it, it worked fine on 3.7V battery power.
If you give me your sketch, I can try to run the same configuration with battery voltage check, BMP280 and LEDs at the same time. You can direct mail me instead of posting it.
Battery voltage measurement can be used with A0 with some ingenuity, but I would recommend using A2 which is not a strap pin. Please also refer to the following link.
‘XIAO ESP32C3, unable to upload sketch or re-write bootloader - #18 by msfujino’
The charge current of the nRF52840 is 50mA or 100mA in the configuration, while the charge current of the ESP32C3 is 370mA. The link below has the results of my measurements. However, if there is some kind of overcurrent protection on the battery side, it should be protected. The 8205A you mention seems to have overcharge detection, but G3JS doesn’t have a datasheet so I don’t know if it can be used. I would recommend that you actually measure the charging current.
‘Charging characteristics of XIAO_nRF52840 and XIAO_ESP32C3’
Hi msfujino,
Thank you for the prompt reply. And I’ll only be happy to send you the code, of course. Where can I find your email address, in your profile? I’m a total newbie here, and haven’t even looked around properly so far.
Your code seemed spot on to me, though, and unless it was just some kind of coincidence, it was showing the correct voltage to the second decimal place. I took a brand new battery from the package, and checked the voltage before I attached it to the circuit, and it was around 3.8V, which is the same result I’ve got from your code. I used the standard resistors, because I don’t have any with tighter tolerance, although I did measure a number of them to select two with as equal resistance as possible. In fact, the only problem was that everything else stopped working, your code was working flawlessly. Now that I changed V0 to V2, though, it’s sending totally random values, although the actual voltage is the same as before.
I’ve read all the stuff from your links when I first visited this forum, and saved and checked your image about charging characteristics. I thing I have datasheets of both components, although I need to find the one for G3JS. If I find it, I can email you both.
Last time I visited this site, I stumbled upon some kind of XIAO dedicated page and there the charging current of ESPC3 was 350mA, not 370. I guess the designer of this board sobered a bit, and tried to tone down that epic choice of parameter a little 
I had other problems with this board today. The upload ended with fatal error a couple of times, with the message about lost connection, and I was using two boards, so it was not a malfunction of just one of them. I’ve read somewhere on this forum if I recall correctly, that I should always reboot by using both buttons in sequence before the upload, but I mostly did not do that and everything worked anyway, and then failed exactly after I did. So all in all, this board seems kind of inconsistent, at least in comparison with other XIAO boards, as much as I can say, although I’m far from being any kind of authority when it comes to programming…
OK, thanks again, I’ll try to find your email address here, and send you the code and datasheets, and if it can’t be found, you can PM me, or however it’s done around here.
Cheers,
Miso
When running on battery power without a PC, if there is a while(!Serial) in the sketch, it waits for the serial monitor and does not work forever.
Did you change the wiring to A0 to A2, and did you change the ADC input pin from A0 to A2 in the sketch?
The charge controller is an ETA4054, and the calculated value is 360mA with the set resistance R22=2.7k in the schematic, and the measured value is 370mA.
The solution to the problem of not being able to upload is on the ESP32C3 wiki.
For direct mail, click on my icon and then click on the message symbol and you will be able to write an email. But for anyone else having the same problem, I think it would be better to post it here.
edit:
I charged a 220mAh battery with built-in protection circuit as a test. The battery is charged at 370mA from XIAO. It seems that the protection circuit does not have a function to suppress the charging current to a safe value, and it is necessary to limit it on the charging circuit side.
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Hi msfujino.
I have stumbled on your post and wanted to replicate what you were doing on a XIAO ESP32-S3, using the A9 analog pin. I tried it with a battery pack I assembled using 2 Li-Ion batteries in parallel with ~10800mAh capacity, so the voltage was (at the time of testing, measured with 2 different measuring instruments) 4.11V. The measured voltage from A9 pin was 4.02V (average over 100 measures, with 100ms between every measurement). I used your code, only modified to measure 100 different values, instead of 15, to get a more realistic average and I added a function that sends the result from the measurement to Slack, as I already had code ready for that and the ESP wasn’t connected to a serial port.
My question is, why is there a 90mV error during measurement and what can I do to avoid it. I tried measuring different voltages from a programmable power supply, and the measurement error is not linear, so adding an offset is not plausible.
Thank you in advance!
i think the ADC is comparing to VCC, so if VCC fluctuates, then the reading also… it is not designed to truly be a multimeter
yall probably got past this already, but i am thinking that something in the circuit is causing a short circuit that is causing a high current draw and browning out the chip… atleast the chip browns out before it burns out…
Hi cgwaltney,
Have you read the following document?
The Vref of the ESP32S3’s ADC is 1.1V, which is internally generated, not VCC; it is not affected by VCC.
And you can use analogReadMillVolts() to get millivolt values with factory calibrated Vref.
‘Analog to Digital Converter (ADC) - ESP32-S3 - — ESP-IDF Programming Guide v4.4 documentation’
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Hi Bklaric,
- the first possibility is variation in the voltage divider resistors. The resistors should be selected and as close to the same value as possible, or the result of analogReadMillVolts() should be corrected for the variation, instead of multiplying by 2.
- The next consideration is the accuracy of your measurement device; you need to decide which of the ADC accuracy or the accuracy of the measurement device to use.
- connecting 100nF between the ADC input pins and GND may help.
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https://docs.espressif.com/projects/arduino-esp32/en/latest/api/adc.html
It is alot of complicated stuff going on in the background that may result in an error between what you read and what it says… like i said before, the chip is not a multimeter, at the end of the day it is taking a binary number and converting it into a decimal number that it presents to you as a millivolt
It is alot of complicated stuff
Have you read the function analogReadMillVolts() to see what complexities are involved?
at the end of the day it is taking a binary number and converting it into a decimal number that it presents to you as a millivolt
Have you estimated how much error is involved in converting binary to decimal and then to millivolts? If you know, please let me know.
I do not know
analogReadResolution
This function is used to set the resolution of analogRead return value. Default is 12 bits (range from 0 to 4095) for all chips except ESP32S3 where default is 13 bits (range from 0 to 8191). When different resolution is set, the values read will be shifted to match the given resolution.
Range is 1 - 16 .The default value will be used, if this function is not used.
Note
For the ESP32, the resolution is between 9 to12 and it will change the ADC hardware resolution. Else value will be shifted.
ADC OneShot mode
The ADC OneShot mode API is fully compatible with Arduino’s analogRead function. When you call the analogRead or analogReadMillivolts function, it returns the result of a single conversion on the requested pin.
analogSetAttenuation
This function is used to set the attenuation for all channels.
Input voltages can be attenuated before being input to the ADCs. There are 4 available attenuation options, the higher the attenuation is, the higher the measurable input voltage could be.
The measurable input voltage differs for each chip, see table below for detailed information.
ESP32ESP32-S2ESP32-C3ESP32-S3
| Attenuation | Measurable input voltage range |
|---|---|
ADC_ATTEN_DB_0 |
100 mV ~ 950 mV |
ADC_ATTEN_DB_2_5 |
100 mV ~ 1250 mV |
ADC_ATTEN_DB_6 |
150 mV ~ 1750 mV |
ADC_ATTEN_DB_11 |
150 mV ~ 3100 mV |
Blockquote
So back to the original question… 90mV is within the stated tollerance of the chip
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yes, take a look at the link i provided
https://docs.espressif.com/projects/arduino-esp32/en/latest/api/adc.html
Thanks for the reply. I will not discuss this any further as the discussion seems to be losing specificity.
I will wait for Bklaric’s reply.
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Thanks for the response msfujino and sorry for the late reply.
- The values of the resistors is not completely perfect, they are 215.4 kOhm and 218.1 kOhm. To account for the different values, I adjusted the multiplication with 2. Instead of 2, I used 2.01253481894, which corresponds to (215.4 + 218.1)/215.4. That seemed to make the error a bit better.
- I measured the battery voltage with 3 different measuring devices, which I tested before with constant voltage, and they are accurate.
- I haven’t tried putting a 100nF decoupling capacitor, but can try it later today.
I tried to ramp up the voltage and measure the difference. I used a lab power supply and got these values:
- Input Voltage: 3.50 V < → Measured Voltage: 3.41263 V
- Input Voltage: 3.60 V <-> Measured Voltage: 3.51939 V
- Input Voltage: 3.70 V <-> Measured Voltage: 3.60384 V
- Input Voltage: 3.80 V < → Measured Voltage: 3.70474 V
- Input Voltage: 3.90 V <-> Measured Voltage: 3.80346 V
- Input Voltage: 4.00 V <-> Measured Voltage: 3.90416 V
- Input Voltage: 4.10 V <-> Measured Voltage: 4.00318 V
- Input Voltage: 4.20 V <-> Measured Voltage: 4.10144 V
The input voltage corresponds to power supply voltage. The measured voltage uses your code for one value, then repeats that 100 times and extracts the average from that. The error fluctuates between 0.081 and 0.099, with the average of 0.093 and the delta difference between min and max error from 0.018.
If you have any more suggestions, how I could solve this, would be pretty nice, as adding an offset is not exactly the solution. But thank you in any case!
Bklaric,
Since the internal circuit is not disclosed, this is a general theory and my imagination.
The reason why the AD conversion value is smaller than the input voltage may be due to the effect of the voltage divider circuit.
There is a sample-and-hold circuit at the input of the AD conversion circuit, which samples and holds the input voltage in a small capacitor and converts the voltage of the held capacitor to AD. If there is no voltage divider circuit, the input voltage is sampled and held with a small time constant, and the input voltage and the capacitor voltage almost match.
However, if the resistance of the voltage divider circuit is as large as 220k, the capacitor voltage rises slowly with a fairly large time constant and is held before it fully reaches the input voltage. As a result, a value lower than the input voltage is AD converted.
To check this, try 2k2 instead of 220k, and the difference will be smaller. Also, if you connect 100nF to the input pin, the difference will be smaller because the capacitor will sample and hold without passing through 220k.
In any case, if you are using an accurate measuring instrument, I would recommend adopting its value to correct the AD conversion result.
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