MicroPython for ODROID-GO - Battery

We will learn how to get the status of the battery with MicroPython in this guide.
The LCD will display how much battery voltage remains in volts.

ODROID-GO has a ~3.7V battery module.
We can read the battery level through one of the 12-bit SAR ADCs which are integrated in ESP32.

These ADCs are:

• ADC1: 8 channels, attached to GPIOs 32-39.
• ADC2: 10 channels, attached to GPIOs 0, 2, 4, 12-15, 25-27.

There are some restrictions for an application's use of ADC2.

The battery is attached to GPIO pin number 36, so we should read a value from that using ADC1.
Fortunately, we can use ADC1 with just putting pin number(32-39) on MicroPython using machine.ADC module.

In this guide, we're going to use that to read the current battery level in volts and display it on the LCD.

First, prepare the code like below to display on the LCD.
We are going to refresh the screen every 1 second so we need to import time module too.

from odroid_go import GO
import time
 
GO.lcd.set_font(GO.lcd.fonts.TT24)
 
 
def show_battery_voltage():
    # need to fill out
 
while True:
    show_battery_voltage()
 
    time.sleep(1)

And we defined one function show_battery_voltage() for showing current voltage on the screen.

Before filling it out, it's important to know the GPIO battery voltage is divided by 2 due to the input limitation of the integrated ADC.
So, if the original value coming from the battery is 3.7V, then the input value to the GPIO pin will be about 1.85V.
Thus, we have to multiply the value by 2 to know the actual voltage.
We use 12 bit SAR ADC for the channel with 11 dB attenuation. We should use these rates to calculate the result as well.

The width and attenuation can be set with

• machine.ADC.width()
• machine.ADC.atten()

so that we can get a voltage value correctly.

We prepared a battery module for ODROID-GO which has get_voltage() function for easy use.
So the code using the module will be shown like the below.

from odroid_go import GO
import time
 
GO.lcd.set_font(GO.lcd.fonts.TT24)
 
 
def show_battery_voltage():
    GO.lcd.erase()
    GO.lcd.set_pos(0, 0)
 
    GO.lcd.print("Current Voltage: " + str(GO.battery.get_voltage()))
 
 
while True:
    show_battery_voltage()
 
    time.sleep(1)

Note that,

• Each ESP32 chip has its Vref value for calibrating an ADC value and has a function for getting correct battery remains. But in MicroPython, we can't use them yet.
  
• To get an ADC value more correctly, consider sampling a reading value. When get_voltage() function in ODROID-GO module called, it reads a ADC value 64 times and returns its average.
  

Save and overwrite this code as boot.py in the ODROID-GO module installation directory.

Upload the boot.py file using rshell or ampy, enter to REPL prompt, and restart ODROID-GO.

Then, press any button to show “Pressed” string besides that button.
As you noticed, you need to keep pressing it until the LCD is updated due to the time.sleep(1) function.

The complete example is available in following path:

• odroid_go/examples/button/battery.py

Copy and paste to try the example.