How to Build a REST API on Raspberry Pi Pico W & Control LED

In this tutorial, you'll learn how to create a REST API using Raspberry Pi Pico W and control two LEDs — one red and one green — via Postman. For this project we are going to use Phew MicroPython library.

This project not only provides a practical introduction to hardware interaction through APIs but also demonstrates the capability of the Raspberry Pi Pico W in building IoT solutions.

🔌 What You'll Learn:

• How to connect to Wi-Fi using Phew library.
• How to Create REST API on Raspberry Pi Pico W.
• Creating the GET API for reading the temperature sensor value on Raspberry Pi Pico W.
• Creating the POST API for controlling the LED from Postman using Raspberry Pi Pico W.

Step 1: Setting Up Hardware

First, 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). Use resistors if desired to protect the LEDs. Connect the shorter leg (cathode) of each LED to the ground.

Step 2: Connecting to Wi-Fi

Before deploying our code, ensure your Raspberry Pi Pico W is connected to the internet through WiFi. Use the following segment in your script to connect:

from phew import connect_to_wifi
ip = connect_to_wifi("YOUR_SSID", "YOUR_PASSWORD")
print("Connected to IP", ip)

Replace "YOUR_SSID" and "YOUR_PASSWORD" with your actual WiFi credentials.

Step 3: Writing the API Code

Utilize the Phew! framework to write and run a web server on the Pico W:

from phew import server
import machine, json

led_green = machine.Pin(0, machine.Pin.OUT)
led_red = machine.Pin(1, machine.Pin.OUT)

Temperature Sensor Endpoint:This endpoint returns the current temperature using the Pico W’s ADC capabilities:

@server.route("/api/temperature", methods=["GET"])
def get_temperature(request):
    adc = machine.ADC(4)
    conversion_factor = 3.3 / 65535
    sensor_value = adc.read_u16() * conversion_factor
    temperature = 27 - (sensor_value - 0.706) / 0.001721
    return json.dumps({"temperature": temperature}), 200, {"Content-Type": "application/json"}

LED Control Endpoint:Create a POST endpoint to control the LEDs:

@server.route("/api/control-led", methods=["POST"])
def ledCommand(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"}

Step 4: Running the Server

Ensure your server is set to run with the following line:

server.run() 

Step 5: Testing with Postman

Open Postman and create a new request to control the LEDs. Set the type to POST and enter your Raspberry Pi Pico W's IP address followed by /api/control-led. In the body of the request, specify the state of each LED in JSON format, e.g., {"ledRed": 1, "ledGreen": 0}.

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Conclusion

By completing this tutorial, you've taken a significant step into the IoT world using the Raspberry Pi Pico W. You've learned how to set up hardware, write a server using the Phew! framework, and control electronic components over the internet. Experiment with different configurations and expand upon this project to explore more possibilities.