nrf24l01

I have 1 master board with nrf24l01 and three slave
I need them to communicate with each other and send sensor data to the master also need the sensor data to be saved on an sd card
the first two slaves have the sensor data
the last slave have relays on it

Have a look at this Simple nRF24L01+ Tutorial.

Wireless problems can be very difficult to debug so get the wireless part working on its own before you start adding any other features.

The examples are as simple as I could make them and they have worked for other Forum members. If you get stuck it will be easier to help with code that I am familiar with. Start by getting the first example to work

There is also a connection test program to check that the Arduino can talk to the nRF24 it is connected to.

A common problem with nRF24 modules is insufficient 3.3v current from the Arduino 3.3v pin. The high-power nRF24s (with the external antenna) will definitely need an external power supply. At least for testing try powering the nRF24 with a pair of AA alkaline cells (3v) with the battery GND connected to the Arduino GND.

The Tutorial includes an example for a master and 2 slaves that can easily be extended to a larger number of slaves.

...R