How to Build REST API on Raspberry Pi Pico W | Control LEDs via Postman

In this tutorial, I will demonstrate how to build REST API on Raspberry Pi Pico W microcontroller board and control the LEDs using Postman client. We will set up endpoints to fetch temperature readings and control LEDs connected to the Raspberry Pi Pico W. We will use the phew library to create the REST API server and interact with the GPIO pins.

We are going to use the Postman for making the GET and POST calls for our REST APIs in order to get the temperature and control 2 LEDs green and red.

Prerequisites

Before we begin, ensure you have the following:

• Raspberry Pi Pico W board
• Micro USB cable
• 2x LEDs of any color
• 3x Male/Male Jumper Wires
• 2x Resistor 330 ohm
• Thonny IDE
• Postman installed on your computer

Step 1: Setup Raspberry Pi Pico W

If you are beginner and just want to start setting up Raspberry Pi Pico W for the first time, I suggest you to follow this detailed guide: How To Get Started With Raspberry Pi Pico in 2024.

Step 2: Prototyping

• Connect your Raspberry Pi Pico W to a breadboard.
• Insert the green LED into one slot and the red LED into another.
• Connect the longer leg (anode) of each LED to separate GPIO pins on the Pico W (we are using GPIO0 for green and GPIO1 for red).
• Insert both the resisters into breadboard and connect LEDs (+) leg in series for both LEDs.
• Connect the shorter leg (cathode) of each LED to the ground.

Step 3: Install Phew Library

To create the REST API we are using Phew library, A small webserver and templating library specifically designed for MicroPython on the Pico W. It aims to provide a complete toolkit for easily creating high quality web based interfaces for your projects.

To install the Phew into Thonny IDE, simple lest approach is to type the below into the Shell (REPL).

pip install micropython-phew

There is other way to install which you follow along the video.

Step 4: Write the Python Code

Create the file name as main.py and write the below code for Build REST API on Raspberry Pi Pico W and Control LEDs via Postman and then upload to Raspberry Pi Pico W:

from phew import server, connect_to_wifi
import machine
import json

# Connect to Wi-Fi
ip = connect_to_wifi("YOUR_SSID", "YOUR_PASSWORD")

# Define LED pins
led_green = machine.Pin(0, machine.Pin.OUT)
led_red = machine.Pin(1, machine.Pin.OUT)

print("Connected to IP: ", ip)

# Endpoint to fetch temperature
@server.route("/api/temperature", methods=["GET"])
def get_temperature(request):
    adc = machine.ADC(4)  # Use ADC pin GP4
    conversion_factor = 3.3 / (65535)  # ADC conversion factor
    sensor_value = adc.read_u16() * conversion_factor
    temperature = 27 - (sensor_value - 0.706) / 0.001721  # Convert sensor value to temperature (formula may vary)
    
    return json.dumps({"temperature": temperature}), 200, {"Content-Type": "application/json"}

# Endpoint to control LEDs
@server.route("/api/control-led", methods=["POST"])
def led_command(request):
    led_red.value(request.data["ledRed"])
    led_green.value(request.data["ledGreen"])
    return json.dumps({"message": "Command sent successfully!"}), 200, {"Content-Type": "application/json"}

# Catchall endpoint for invalid URLs
@server.catchall()
def catchall(request):
    return json.dumps({"message": "URL not found!"}), 404, {"Content-Type": "application/json"}

# Run the server
server.run()

Replace "YOUR_SSID" and "YOUR_PASSWORD" with your Wi-Fi network credentials.

You can get the same from RajivCodeLab’s Gist.

Step 5: Use Postman to Interact with the APIs

We are going to use Postman for making the GET and POST calls for our REST APIs in order to get the temperature and control 2 LEDs (green and red).

1. Open Postman on your computer.
2. Send a GET request to http://<raspberry_pi_ip>/api/temperature to fetch temperature readings from the sensor.
3. Send a POST request to http://<raspberry_pi_ip>/api/control-led with the following JSON body to control the LEDs:

{
    "ledRed": 1,
    "ledGreen": 0
}

This will turn on the red LED and turn off the green LED.

Support the Creator

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Conclusion

In this tutorial, we learned how to build a simple REST API on Raspberry Pi Pico W to fetch temperature readings and control LEDs using the phew library. You can further extend this project by adding more endpoints for additional functionalities and integrating it with other IoT devices.

FAQs: