longer range TCPIP via NRF24L01 for a pair of Raspberry PIs

Intro

This tutorial is trying to use NRF24L01 to create a TCP/IP link between two Raspberry Pi boards. Due to long range of NRFs, some of those have 1800 meter wireless range, it would be good to have a TCPIP link between two RPi via NRFs so it would be possible to have a TCPIP connection between two RPi in longer range. The onboard wifi of RPi cannot do long ranges like 50 meter even in clear sight.

schematics

Hardware Configuration

1. wiring: Here is how I did connect the module to the RPi as described in the main RF24 documentation here.
2. Noise on 3.3v on RPi: Put some capacitor or L-C filter to reduce the noise on 3.3v supply from RPi.
3. Shielding PA/LNA module: Shield your radio module, if it has none. See more details in the RF24 Common Issues document

Software Configuration

1. Enable SPI from raspi-config. Select "Interface Options" -> "SPI" -> "Yes" -> "Ok", then exit and reboot the RPi (sudo reboot).
2. Install nRF24 library stack on each machine. See more detail in the RF24 docs.

sudo apt-get update
sudo apt-get upgrade
wget https://raw.githubusercontent.com/nRF24/.github/main/installer/install.sh
chmod +x install.sh
./install.sh

Installer will promp which modules you want to install. I did installed all modules: "RF24", "RF24Network" "RF24Mesh" "RF24Gateway". Also please select SPIDEV driver during installation.

after installation done, and if there are no errors in the process, there will be these directories inside the RPi:

~/rf24libs/RF24
~/rf24libs/RF24Network
~/rf24libs/RF24Gateway
~/rf24libs/RF24Mesh

Next we need to choose a master/primary node (as discussed here). so one RPi will be primary, and another one will be secondary. we'll use the official example named ncurses in RF24 repo to establish the network. this code is already cloned to local device in process of installation. so we need to have some edits on the code. On the Master/Primary machine no need to do edits, but on the secondary machine we need to edit ~/rf24libs/RF24Gateway/examples/ncurses/RF24Gateway_ncurses.cpp file, first lines of method main()

Before edit (first lines)

int main()
{
 
    gw.begin();
    //mesh.setStaticAddress(8, 1);
 
    //uint8_t nodeID = 22;
    //gw.begin(nodeID,3,RF24_2MBPS);
 
    //uint16_t address = 0;
    //gw.begin(address,3,RF24_2MBPS);

after edit:

int main()
{
 
    //gw.begin();
    //mesh.setStaticAddress(8, 1);
 
    uint8_t nodeID = 3;
    gw.begin(nodeID);
 
    //uint16_t address = 0;
    //gw.begin(address,3,RF24_2MBPS);

Again, the above edit is only done in the secondary machine, the primary machine needs no edits.

Next, we need to recompile the ncurses example and run it in the terminal:

cd ~/rf24libs/RF24Gateway/examples/build
make

Primary machine config

sudo ip tuntap add dev tun_nrf24 mode tun user pi multi_queue
sudo ifconfig tun_nrf24 10.11.2.2/24

The following commands can be run to modify the default TCP/IP window sizes. This can severely impact other network functionality. Run sudo sysctl net.ipv4.tcp_wmem and sudo sysctl net.ipv4.tcp_rmem to get the defaults so they can be restored.

sudo sysctl net.ipv4.tcp_wmem="1500 1500 1500"
sudo sysctl net.ipv4.tcp_rmem="1500 1500 1500"

These changes are only temporary and need to be run each time after reboot of the operating system.

Secondary machine config

sudo ip tuntap add dev tun_nrf24 mode tun user pi multi_queue
sudo ifconfig tun_nrf24 10.11.2.3/24

The following commands can be run to modify the default TCP/IP window sizes. This can severely impact other network functionality. Run sudo sysctl net.ipv4.tcp_wmem and sudo sysctl net.ipv4.tcp_rmem to get the defaults so they can be restored.

sudo sysctl net.ipv4.tcp_wmem="1500 1500 1500"
sudo sysctl net.ipv4.tcp_rmem="1500 1500 1500"

These changes are only temporary and need to be run each time after reboot of the operating system.

Run the ncurses example on both machines

cd ~/rf24libs/RF24Gateway/examples/build/ncurses
./RF24Gateway_ncurses

Done. The primary machine IP is 10.11.2.2, and the secondary machine IP is 10.11.2.3. One could ping machines from each other.

pi@pi:~ $ ping 10.11.2.2 -c10
PING 10.11.2.2 (10.11.2.2) 56(84) bytes of data.
64 bytes from 10.11.2.2: icmp_seq=1 ttl=64 time=15.6 ms
64 bytes from 10.11.2.2: icmp_seq=2 ttl=64 time=13.6 ms
64 bytes from 10.11.2.2: icmp_seq=3 ttl=64 time=14.2 ms
64 bytes from 10.11.2.2: icmp_seq=4 ttl=64 time=14.8 ms
64 bytes from 10.11.2.2: icmp_seq=5 ttl=64 time=13.0 ms
64 bytes from 10.11.2.2: icmp_seq=6 ttl=64 time=14.9 ms
64 bytes from 10.11.2.2: icmp_seq=7 ttl=64 time=14.0 ms
64 bytes from 10.11.2.2: icmp_seq=8 ttl=64 time=14.0 ms
64 bytes from 10.11.2.2: icmp_seq=9 ttl=64 time=14.1 ms
64 bytes from 10.11.2.2: icmp_seq=10 ttl=64 time=14.7 ms
 
--- 10.11.2.2 ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 9013ms
rtt min/avg/max/mdev = 13.014/14.281/15.603/0.698 ms

The resulting latency when pinging primary machine from secondary is about 14 millisecond. Let's check the transfer speed. The speed, most of the times, is about 10 kB/s (equal to 100K bits per second) but sometimes less. 5 kB/s should be good approximation for an average.