main.c

#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/adc.h"
#include "lib/fonts.h"
#include "lib/st7735.h"

/*
this task covers how to use the on-board temperature sensor in the RP2040 chip on the Raspberry pi Pico
it uses the analogue to digital converter (ADC) in the Pico to read the internal temperature of the RP2040 and
does the necessary data conversion to output the temperature of the chip

also covers how to perform the required data processing to take the raw ADC output and convert it
into a voltage and then into temperature

the temperature sensor might not be calibrated so temperatures might differ in different
boards due to manufacturing inconsistencies
as such, if you will be using this in a serious project that requires an accurate temperature value,
I would recommend using an external sensor.
*/

int main() {

    stdio_init_all();  // Initialise serial in/output

    //Configure ADC
    adc_init();
    adc_set_temp_sensor_enabled(true);  //Enable temperature sensor
    adc_select_input(4);  //Select fifth channel of the adc as the input

    sleep_ms(1000);  // Wait 1 sec
    ST7735_Init();  // Initialise the screen

    //Update temperature display every second
    //Infinite loop
    while (1) {
        uint16_t raw = adc_read(); //Define a variable to store the raw output value from the adc

        //Do the conversion
        const float conversion = 3.3f / (1 << 12);
        float voltage = raw * conversion; // convert raw value to voltage
        float temperature = 27 - (voltage - 0.706) / 0.001721; // convert voltage to temperature value

        char strArray[25];
        sprintf(strArray, "Temperature: %d", (int) temperature); //store output on char buffer

        ST7735_FillScreen(ST7735_BLACK);//set screen color
        ST7735_WriteString(0, 0, strArray, Font_16x26, ST7735_GREEN, ST7735_BLACK);//display temperature on screen

        //can also use any other function from the library to display the temperature differently

        //wait 1 sec
        sleep_ms(1000);
    }
}