Building a Temperature Sensor with Raspberry Pi Pico's RP2040

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The Raspberry Pi Pico, powered by the RP2040 microcontroller, is a versatile and affordable development board. One of its hidden gems is the on-board temperature sensor, which allows you to measure the chip's temperature itself. In this blog, we'll explore how to utilize this sensor and create a simple temperature monitoring project.


 Introduction to the Temperature Sensor


The RP2040's temperature sensor works by measuring the voltage across an internal diode within the chip. Keep in mind that this diode voltage doesn't directly represent the ambient room temperature; instead, it reflects the chip's temperature. To convert this voltage to temperature, we'll use the following equation:


Temperature (°C)= 27 -( Voltage - 0.706 )/0.001721


Setting Up the Project


Prerequisites


Before we dive into the code, make sure you have the following:


- A Raspberry Pi Pico

- A USB cable for programming

- A development environment (such as Thonny or Visual Studio Code)


Writing the Code


1. CMakeLists.txt:

   - Start by creating a new project using the standard CMakeLists format.

   - Add the necessary libraries: `pico_stdlib` and `hardware_adc`.

   - Enable USB serial output.


2. C File:

   - Include the required libraries: `stdio.h`, `pico/stdlib.h`, and `hardware/adc.h`.

   - Initialize the standard I/O (`stdio_init_all()`).

   - Initialize the ADC (`adc_init()`).

   - Enable the temperature sensor (`adc_set_temp_sensor_enabled(true)`).

   - Select the ADC input corresponding to the 5th ADC channel (`adc_select_input(4)`).


3. Temperature Calculation:

   - In an infinite loop:

     - Read the raw ADC value (`adc_read()`).

     - Convert the raw value to voltage using the conversion factor.

     - Calculate the temperature using the equation mentioned earlier.

     - Print the temperature over the USB serial interface.

     - Sleep for a second (`sleep_ms(1000)`).


Putting It All Together


Now you're ready to measure the temperature of your RP2040! Build the project, upload it to your Pico, and open your preferred serial monitor (baud rate: 115,200). You'll see the temperature output change as the chip's temperature fluctuates.


Keep in mind that the sensor isn't perfectly calibrated, so your readings might differ from room temperature. But that's part of the fun—exploring and tinkering with the RP2040!



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