Display the internal temperature of an RP2040 to an I2C LCD

In this article we look at display t he internal temperature of an RP2020 to an I2C 16×2 LCD to a raspberry Pi Pico

The internal temperature sensor that comes with the Raspberry Pi Pico is connected to one of the Analog-to-Digital Converters. The ADC pin supports a range of values, which is determined by the input voltage applied to the pin.

In the Raspberry Pi Pico Board, the ADC pins support 12-bits, which means that the value can go from 0 to 4095.

The MicroPython code though can scale the ADC values to a 16-bit range  which means the range of values that are available are actually 0 to 65535. The microcontroller operates at 3.3 V, this means that an ADC pin will return a value of 65535 at 3.3 V or 0 when there is 0v. So with some simple code we can easily get the value which we can then display on an LCD

The temperature sensor does not connect to a physical pin on the board but is actually ADC4.

Parts Required

 

Name	Link
Pico	Raspberry Pi Pico Development Board
I2C lCD	Aliexpress link
Connecting cables	Aliexpress product link Lysee 3D Printer Parts & Accessories – AHT20 Temperature and Humidity Sensor Module DHT11 Upgrade I2C XD Humidity Sensor Probe – (Color: Green) Ebay link

 

Schematic/Connection

To connect the display to your Raspberry PI Pico requires just 4 wires, you just need to wire the Vcc and GND PINs from display to VBuS and a GND PINs of RPI Pico, then SDA and SCL PINs from the module to suitable SDA and SCL PINs from Raspberry PI Pico

Here is a layout in fritzing to show this

 

Code Example

I use thonny for all development

Now its important to verify the I2C address of your LCD

sdaPIN=machine.Pin(0)
sclPIN=machine.Pin(1)
i2c=machine.I2C(0,sda=sdaPIN, scl=sclPIN, freq=400000)
devices = i2c.scan()
if len(devices) == 0:
 print("No i2c device !")
else:
 print('i2c devices found:',len(devices))
for device in devices:
 print("Hexa address: ",hex(device))

You will see the I2C address in the REPL

You then need to copy 2 libraries to your Pico filesystem

In Thonny, go to top menu File => Save Copy => Raspberry Pi Pico and save each file to the board with the same name as downloaded and with a .PY extension when saving it to the board.

https://github.com/T-622/RPI-PICO-I2C-LCD/blob/main/lcd_api.py

https://github.com/T-622/RPI-PICO-I2C-LCD/blob/main/pico_i2c_lcd.py

Now that you have done all that, lets create a simple clock which will display the date on line 1 and the time on line 2

Now lets look a complete example

from machine import I2C,Pin,ADC #import libraries to handle Pins, I2C and ADC
from time import sleep 
from lcd_api import LcdApi
from pico_i2c_lcd import I2cLcd

I2C_ADDR = 0x27
totalRows = 2
totalColumns = 16
#Internal Temperature sensor is connected to ADC 4
sensor_temp = ADC(4)
conversion_factor = 3.3/65535

#get temperature value from ADC 4 internal sensor
def get_temperature():
    reading = sensor_temp.read_u16() * conversion_factor
    temperature = 27 - (reading - 0.706)/0.001721
    return temperature

i2c = I2C(0, sda=machine.Pin(0), scl=machine.Pin(1), freq=400000)
lcd = I2cLcd(i2c, I2C_ADDR, totalRows, totalColumns)

#define a customized LCD icon for º (degree sign)
degree = bytearray([0x1c,0x14,0x1c,0x00,0x00,0x00,0x00,0x00])
#degree sign 'º' will be used as chr(0) in program
lcd.custom_char(0, degree)

while True:       
    lcd.putstr("Temperature:\n"+str(get_temperature())+" C"+chr(0)) #display temperature to LCD
    sleep(4)
    lcd.clear()

Now keep in mind this is internal temperature for t he Rp2040 and will all likelihood not be the same as  the ambient temperature of the surroundings. We will look at temperature sensors in future examples.