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8.12 Read data from bluetooth

In this project, the Pico 2 W functions as a peripheral device in a Bluetooth Low Energy (BLE) network. It offers a custom BLE service to control an LED-based traffic light system. This service includes a writable characteristic, allowing a central device, such as a smartphone or computer, to send commands. The Pico board processes these commands to toggle the red, yellow, or green LEDs, simulating traffic light operations. Debugging information, including received commands, is displayed on the serial monitor to assist development.

The onboard LED indicates the connection status: it lights up when a central device is connected and turns off when the connection is lost.

1. Build the circuit

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Pico 2 W Starter Kit	450+	Pico 2 W Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Getting to Know Pico 2 W	1
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	Resistor	3(220Ω)	BUY
6	LED	3	BUY

2. Upload the code

Copy the following code into your IDE. Alternatively, you can find it in our repository at the path: pico-2w-kit/micropython/iot/8.12-read_from_ble/ble_trafficlight.py.

Note: This code depends on the ble_advertising.py and ble_simple_peripheral.py file. Make sure to upload it to the Pico board before running the script.

# Import necessary modules
from machine import Pin
import bluetooth
from ble_example.ble_simple_peripheral import BLESimplePeripheral

# Create a Bluetooth Low Energy (BLE) object
ble = bluetooth.BLE()

# Create an instance of the BLESimplePeripheral class with the BLE object
sp = BLESimplePeripheral(ble,"pico2w")

# Create a Pin object for the onboard LED, configure it as an output
led = Pin("LED", Pin.OUT)

red = machine.Pin(13, machine.Pin.OUT)
yellow = machine.Pin(12, machine.Pin.OUT)
green = machine.Pin(11, machine.Pin.OUT)

def update_traffic(data):

    decoded_data = data.decode('utf-8').rstrip('\r\n')

    red.off()
    green.off()
    yellow.off()

    if decoded_data == "R" or decoded_data == "r":
        red.on()
    elif decoded_data == "G" or decoded_data == "g":
        green.on()
    elif decoded_data == "Y" or decoded_data == "y":
        yellow.on()


# Define a callback function to handle received data
def on_rx(data):
    print("Data received: ", data)  # Print the received data

    update_traffic(data)

# Start an infinite loop
while True:
    if sp.is_connected():  # Check if a BLE connection is established
        sp.on_write(on_rx)  # Set the callback function for data reception

3. Write data to bluetooth

To interact with the services and characteristics defined in this code, use a generic Bluetooth® Low Energy central app, such as LightBlue (available for iOS and Android) or nRF Connect (for Android).

This section uses LightBlue as an example to demonstrate how to control the Pico 2 W’s features via Bluetooth.

1. Install LightBlue

   Download the LightBlue app from the App Store (for iOS) or Google Play (for Android).

   

2. Connect Pico 2 W

   Launch LightBlue and enable location and Bluetooth permissions if prompted. On the Peripherals page, search for “pico” in the search bar, and tap to connect to the Pico 2 W device.

   

3. Send data to toggle the light

   After connecting, LightBlue displays detailed information about the Pico 2 W Bluetooth device. Scroll down to locate the Service (6E400001-B5A3-F393-E0A9-E50E24DCCA9E) and Characteristic (6E400002-B5A3-F393-E0A9-E50E24DCCA9E).

   Tap the characteristic 6E400002-B5A3-F393-E0A9-E50E24DCCA9E. The app shows the properties of this characteristic: it’s writable.

   

   In the top-right corner, select “UTF-8 String” as the data type.

   

   Click “Write New Value” and input R. This character will be sent to the Pico board via Bluetooth. The Pico board will interpret the received character and control specific LEDs accordingly:

   • r lights up the red LED

   • y lights up the yellow LED

   • g lights up the green LED