Tag Archives: wireless

In this tuturial, we will establish a wireless communication between two Raspberry Pi Pico equipped with an nRF24L01 module each. We will use the MicroPython languge to program our Raspberry Pi Pico.

nRF24L01 modules are designed to transmit the information at a 2.4 GHz radio frequency. Each module can transmit and receive signals. The range can be a few tens of meters.

Connections

You need to have a pair of nRF24L01 modules. Depending on their brand, you may find:

• Green modules with 10 clearly marked pins
• Black modules with 8 pins that have no identification.

Wire each of your Raspberry Pi Pico to an nRF24L01 module as follows:

• VCC (nRF24L01) => 3.3V output (Raspberry Pi Pico).
• GND (nRF24L01) => GND (Raspberry Pi Pico).
• SCK (nRF24L01) => GP6 (Raspberry Pi Pico).
• MOSI (nRF24L01) => GP7 (Raspberry Pi Pico).
• MISO (nRF24L01) => GP4 (Raspberry Pi Pico).
• IRQ (nRF24L01) => not connected
• CE (nRF24L01) => GP12 (Raspberry Pi Pico).
• CSN (nRF24L01) => GP5 (Raspberry Pi Pico).

We highly recommend that you add a 10 µF capacitor between the GND and VCC pins of the nRF24L01 module. This is a solution to consider if you notice erratic operation.

Installing the nrf24l01.py library

After downloading the nrf24l01.py library, it is important to install the nrf24l01.py file in the flash memory of the Raspberry Pi Pico (using, for example, Thonny).

This library is accompanied by a very well done program called “nrf24l01test.py”. To use it with the Raspberry Pi Pico, however, you will need to change the pin numbers at the start of the program.
Based on this example, you’ll find two separate scripts below. These scripts was designed to be used simultaneously on two different Raspberry Pi Picos. The first script is for the transmitter, and the other one is for the receiver.

The transmitter’s script

Each second, this Raspberry Pi Pico increments an integer number and sends it to the nRF24L01 module. It then checks whether it receives a response from the receiver.

"""
nRF24L01 transmitter
Raspberry Pi Pico and nRF24L01 module
Once per second, a numerical value is sent, and we
checks if we receive a response.
For more info:
www.bekyelectronics.com/raspberry-pico-nrf25l01-micropython/
"""
import ustruct as struct
import utime
from machine import Pin, SPI
from nrf24l01 import NRF24L01

# pin definition for the Raspberry Pi Pico:
myPins = {"spi": 0, "miso": 4, "mosi": 7, "sck": 6, "csn": 5, "ce": 12}

# Addresses (little endian)
pipes = (b"\xe1\xf0\xf0\xf0\xf0", b"\xd2\xf0\xf0\xf0\xf0")

print("NRF24L01 transmitter")

csn = Pin(myPins["csn"], mode=Pin.OUT, value=1)
ce = Pin(myPins["ce"], mode=Pin.OUT, value=0)
nrf = NRF24L01(SPI(myPins["spi"]), csn, ce, payload_size=8)

nrf.open_tx_pipe(pipes[0])
nrf.open_rx_pipe(1, pipes[1])
nrf.start_listening()

counter = 0  # Increase the value by 1 with each emission

while True:
    # Stop listening, time to send a message
    nrf.stop_listening()
    
    counter = counter + 1 # preparing the message to send
    print("sending:",  counter)
    
    try:
        nrf.send(struct.pack("i",  counter)) # sending the message
    except OSError:
        pass

    # Listen if the other Pico answers us
    nrf.start_listening()

    # Wait for 250ms max
    start_time = utime.ticks_ms()
    timeout = False
    while not nrf.any() and not timeout:
        if utime.ticks_diff(utime.ticks_ms(), start_time) > 250:
            timeout = True

    if timeout:  # no response received
        print("failure, no response")

    else:  # a response has been received
        (response,) = struct.unpack("i", nrf.recv())
        print ("response recue:", response)

    # Wait a second before sending the next message
    utime.sleep_ms(1000)

The receiver’s script

If this Raspberry Pi Pico receives a message from the transmitter, it calculates the modulo of the number received and returns the result to the transmitter. It therefore returns the number “0” when it receives an even number, and the number “1” when it receives an odd number.

"""
nRF24L01 receiver
Raspberry Pi Pico and nRF24L01 module.
If an integer is received, it is acknowledged by flipping its modulo.
For more info:
www.bekyelectronics.com/raspberry-pico-nrf25l01-micropython/
"""
import ustruct as struct
import utime
from machine import Pin, SPI
from nrf24l01 import NRF24L01
from micropython import const

# delay between receiving a message and waiting for the next message
POLL_DELAY = const(15)
# Delay between receiving a message and sending the response
# (so that the other pico has time to listen)
SEND_DELAY = const(10)

# Pico pin definition:
myPins = {"spi": 0, "miso": 4, "mosi": 7, "sck": 6, "csn": 5, "ce": 12}

# Addresses
pipes = (b"\xe1\xf0\xf0\xf0\xf0", b"\xd2\xf0\xf0\xf0\xf0")

csn = Pin(myPins["csn"], mode=Pin.OUT, value=1)
ce = Pin(myPins["ce"], mode=Pin.OUT, value=0)
nrf = NRF24L01(SPI(myPins["spi"]), csn, ce, payload_size=8)

nrf.open_tx_pipe(pipes[1])
nrf.open_rx_pipe(1, pipes[0])
nrf.start_listening()

print("nRF24L01 receiver; waiting for the first post...")

while True:
    if nrf.any(): # we received something
        while nrf.any():
            buf = nrf.recv()
            counter = struct.unpack("i", buf)
            print("message received:", counter[0])
            utime.sleep_ms(POLL_DELAY) # delay before next listening
            
        response = counter[0]%2 # preparing the response

        utime.sleep_ms(SEND_DELAY) # Give the other Pico a brief time to listen
        nrf.stop_listening()
        try:
            nrf.send(struct.pack("i", response))
        except OSError:
            pass
        print("reply sent:", response)
        nrf.start_listening()

That’s it, this is how you establish wireless communication between your Picos using NRF24L01. I hope this tutorial was helpful for you. You can check other tutorials from this link.