examples_linux/getting_started.py

Written by 2bndy5 in 2020

This is a simple example of using the RF24 class on a Raspberry Pi.

Remember to install the Python wrapper, then navigate to the "RF24/examples_linux" folder.
To run this example, enter

python3 getting_started.py 

and follow the prompts.

Note

this example requires python v3.7 or newer because it measures transmission time with time.monotonic_ns().

"""
A simple example of sending data from 1 nRF24L01 transceiver to another.
This example was written to be used on 2 devices acting as 'nodes'.
 
See documentation at https://nRF24.github.io/RF24
"""
 
import time
import struct
from RF24 import RF24, RF24_PA_LOW, RF24_DRIVER
 
print(__file__)  # print example name
 
 
CSN_PIN = 0  # GPIO8 aka CE0 on SPI bus 0: /dev/spidev0.0
if RF24_DRIVER == "MRAA":
    CE_PIN = 15  # for GPIO22
elif RF24_DRIVER == "wiringPi":
    CE_PIN = 3  # for GPIO22
else:
    CE_PIN = 22
radio = RF24(CE_PIN, CSN_PIN)
 
# initialize the nRF24L01 on the spi bus
if not radio.begin():
    raise RuntimeError("radio hardware is not responding")
 
# For this example, we will use different addresses
# An address need to be a buffer protocol object (bytearray)
address = [b"1Node", b"2Node"]
# It is very helpful to think of an address as a path instead of as
# an identifying device destination
 
 
# to use different addresses on a pair of radios, we need a variable to
# uniquely identify which address this radio will use to transmit
# 0 uses address[0] to transmit, 1 uses address[1] to transmit
radio_number = bool(
    int(input("Which radio is this? Enter '0' or '1'. Defaults to '0' ") or 0)
)
 
# set the Power Amplifier level to -12 dBm since this test example is
# usually run with nRF24L01 transceivers in close proximity of each other
radio.setPALevel(RF24_PA_LOW)  # RF24_PA_MAX is default
 
# set the TX address of the RX node into the TX pipe
radio.openWritingPipe(address[radio_number])  # always uses pipe 0
 
# set the RX address of the TX node into a RX pipe
radio.openReadingPipe(1, address[not radio_number])  # using pipe 1
 
# To save time during transmission, we'll set the payload size to be only
# what we need. A float value occupies 4 bytes in memory using
# struct.pack(); "f" means an unsigned float
radio.payloadSize = struct.calcsize("f")
 
# for debugging, we have 2 options that print a large block of details
# (smaller) function that prints raw register values
# radio.printDetails()
# (larger) function that prints human readable data
# radio.printPrettyDetails()
 
# using the python keyword global is bad practice. Instead we'll use a 1 item
# list to store our float number for the payloads sent/received
payload = [0.0]
 
 
def master():
    """Transmits an incrementing float every second"""
    radio.stopListening()  # put radio in TX mode
    failures = 0
    while failures < 6:
        # use struct.pack() to packet your data into the payload
        # "<f" means a single little endian (4 byte) float value.
        buffer = struct.pack("<f", payload[0])
        start_timer = time.monotonic_ns()  # start timer
        result = radio.write(buffer)
        end_timer = time.monotonic_ns()  # end timer
        if not result:
            print("Transmission failed or timed out")
            failures += 1
        else:
            print(
                "Transmission successful! Time to Transmit:",
                f"{(end_timer - start_timer) / 1000} us. Sent: {payload[0]}",
            )
            payload[0] += 0.01
        time.sleep(1)
    print(failures, "failures detected. Leaving TX role.")
 
 
def slave(timeout=6):
    """Listen for any payloads and print the transaction
 
    :param int timeout: The number of seconds to wait (with no transmission)
        until exiting function.
    """
    radio.startListening()  # put radio in RX mode
 
    start_timer = time.monotonic()
    while (time.monotonic() - start_timer) < timeout:
        has_payload, pipe_number = radio.available_pipe()
        if has_payload:
            # fetch 1 payload from RX FIFO
            buffer = radio.read(radio.payloadSize)
            # use struct.unpack() to convert the buffer into usable data
            # expecting a little endian float, thus the format string "<f"
            # buffer[:4] truncates padded 0s in case payloadSize was not set
            payload[0] = struct.unpack("<f", buffer[:4])[0]
            # print details about the received packet
            print(
                f"Received {radio.payloadSize} bytes",
                f"on pipe {pipe_number}: {payload[0]}",
            )
            start_timer = time.monotonic()  # reset the timeout timer
 
    print("Nothing received in", timeout, "seconds. Leaving RX role")
    # recommended behavior is to keep in TX mode while idle
    radio.stopListening()  # put the radio in TX mode
 
 
def set_role() -> bool:
    """Set the role using stdin stream. Timeout arg for slave() can be
    specified using a space delimiter (e.g. 'R 10' calls `slave(10)`)
 
    :return:
        - True when role is complete & app should continue running.
        - False when app should exit
    """
    user_input = (
        input(
            "*** Enter 'R' for receiver role.\n"
            "*** Enter 'T' for transmitter role.\n"
            "*** Enter 'Q' to quit example.\n"
        )
        or "?"
    )
    user_input = user_input.split()
    if user_input[0].upper().startswith("R"):
        if len(user_input) > 1:
            slave(int(user_input[1]))
        else:
            slave()
        return True
    if user_input[0].upper().startswith("T"):
        master()
        return True
    if user_input[0].upper().startswith("Q"):
        radio.powerDown()
        return False
    print(user_input[0], "is an unrecognized input. Please try again.")
    return set_role()
 
 
if __name__ == "__main__":
    try:
        while set_role():
            pass  # continue example until 'Q' is entered
    except KeyboardInterrupt:
        print(" Keyboard Interrupt detected. Powering down radio.")
        radio.powerDown()
else:
    print("    Run slave() on receiver\n    Run master() on transmitter")