Using RF Modules with Raspberry Pi Pico

[Marin-Johnson]

Hello -

I have 2 Raspberry Pi Picos running MicroPython. I am trying to use a 433 MHz RF transmitter on one Pico and a 433 MHz RF receiver on the other Pico. I am currently using UART to transmit and receive data:

# Receiver

import os
import machine
from time import sleep

uart = machine.UART(0, 4800)
print(uart)

led = machine.Pin(25, machine.Pin.OUT)

b = None
msg = ""

while True:
    if uart.any():
        b = uart.readline()
        try:
            msg = b.decode('utf-8')
            print(str(msg))
        except:
            print("Failed (" + str(type(b)) + "): " + str(b))
            pass
        
    led.toggle()
    sleep(1)

and

# Transmitter

import os
import machine
from time import sleep

uart = machine.UART(0, 4800)
print(uart)

led = machine.Pin(25, machine.Pin.OUT)

while True:
    sleep(5)
    led.toggle()
    uart.write('Hello, World!')

But the receiver prints stuff like this even when the transmitter is not transmitting. (I can't paste it here as it messes with the formatting)

As an experiment, I connected the TX on one Pico to the RX of the other pico, and it was able to send the data successfully. Therefore, I believe it is the transmitter and receiver getting interference from other signals.

My Question:

Arduino has libraries for packet radio. (see this) Is there anything similar in MicroPython or for the Raspberry Pi Pico?

Thanks.

[peterhinch]

Yes, but not for these modules. See NRF24l01 which is a 2.4GHz radio.

Unless a receiver is explicitly designed for use with a UART you can't stick a UART on a receiver and expect it to work. Many receivers output garbage in the absence of a signal.

[Marin-Johnson]

Thanks, will use these instead.

[Marin-Johnson]

Unless a receiver is explicitly designed for use with a UART you can't stick a UART on a receiver and expect it to work. Many receivers output garbage in the absence of a signal.

I thought UART should work, as these modules say they support a "Direct serial interface." They also say

The CMOS-compatible data input on Pin 2 is normally supplied with a serial bit stream from a microprocessor or encoder, but it can also be used with standard UARTs.

So why does UART not work as these modules claim it does?

[scruss]

These modules are a step above the horrible cheap ones I've seen in the past. But to echo Peter's answer, a quote from the https://linxtechnologies.com/wp/wp-content/uploads/txm-fff-lr.pdf:

… Linx RF modules do not encode or packetize the signal content in any manner

So you have to encode the data yourself, usually a Manchester encoding.

The receiver will typically appear to be only picking up noise. That's because they usually have automatic gain control, and a transmitter has to send a series of training pulses before the data packet to get the receiver's attention. Since there's no error correction, you have to build that into your protocol, too. You also have to be really careful about building the right antenna. Without a library for MicroPython, this will be a lot of work

Peter's NRF recommendation is a good one: they do all the work of building a protocol.

[Marin-Johnson]

Got it, thanks.

[peterhinch]

This library may be of use for extending the basic functionality of the NRF24l01.