# How to Measure Battery Voltage?

**URL:** https://xrp.discourse.group/t/how-to-measure-battery-voltage/590
**Category:** Hardware
**Created:** [January 8, 2025, 3:56am UTC](https://xrp.discourse.group/t/how-to-measure-battery-voltage/590 "2025-01-08T03:56:38Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![swansfan](https://avatars.discourse-cdn.com/v4/letter/s/9d8465/32.png) [@swansfan](https://xrp.discourse.group/u/swansfan)
#### Post date: [January 8, 2025, 3:56am UTC](https://xrp.discourse.group/t/how-to-measure-battery-voltage/590/1 "2025-01-08T03:56:38Z")

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Hello,

I would like to learn how to measure the remaining battery charge using GPIO28.

I have tried reading the value on GPIO28 but I may not be doing this correctly and I am also not sure how to convert reading this to the correct voltage using the XRP controller board.

My attempt is below.

```auto
from XRPLib.defaults import *
from machine import Pin, ADC
from time import sleep

pinVin = ADC(Pin(28))

while True:
  voltage = (pinVin.read_u16()/65535) # am unsure about this calculation 
  print(voltage)
  sleep(0.5)

```

Thanks in advance for any advice/assistance.

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### Author: ![SparkFro](https://yyz1.discourse-cdn.com/flex011/user_avatar/xrp.discourse.group/sparkfro/32/12_2.png) [@SparkFro](https://xrp.discourse.group/u/SparkFro)
#### Post date: [January 8, 2025, 5:42pm UTC](https://xrp.discourse.group/t/how-to-measure-battery-voltage/590/2 "2025-01-08T17:42:15Z")

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You’re close! 2 things you need to add:

1. Multiply by the reference voltage, which is 3.3V
2. Multiply by the voltage divider ratio, which is about 4
  1. If you look at the [XRP Control Board schematic](https://docs.sparkfun.com/SparkFun_XRP_Controller/assets/hardware_files/XRP_Controller.pdf), the “VIN Measurement” section in the middle includes a voltage divider circuit (just 2 resistors) to allow measurements above 3.3V. Because a 100k and 33k resistors are used, the output voltage is `(100 + 33) / 33 = 4.030303...` times smaller than the input voltage (4.030303… is close enough to 4 for me 😉)

So just need to do:

`voltage = (pinVin.read_u16() / 65535 * 3.3 * 4)`

Note that due to imperfections of the ADC on the XRP, the measured voltage may fluctuate a little, and it may not be exactly the same as what your voltmeter measures.

I’ve also put a [feature request into XRPLib](https://github.com/Open-STEM/XRP_MicroPython/issues/75) for a pre-defined `get_input_voltage()` function to be added, hopefully we’ll see that in the future!

Hope this helps!

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<div class="post-metadata">

### Author: ![swansfan](https://avatars.discourse-cdn.com/v4/letter/s/9d8465/32.png) [@swansfan](https://xrp.discourse.group/u/swansfan)
#### Post date: [January 8, 2025, 11:16pm UTC](https://xrp.discourse.group/t/how-to-measure-battery-voltage/590/3 "2025-01-08T23:16:36Z")

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Brilliant!

Thanks for taking the time to post such a detailed answer, much appreciated.