nRF24L01/nRF24L01+ module principle introduction

The nRF24L01 module provides a very efficient and inexpensive way of communication, the nRF24l01 module is actually a radio transceiver module, which operates on the 2.4GHz frequency. This module has the ability to send and receive data simultaneously and can be used in various IOT projects to create wireless connections. By showing it's a very small module, but its functionality is amazing.

nRF24L01/nRF24L01+ modules

The nRF24L01 is a single-chip wireless transceiver chip produced by Nordic Semiconductor. Its radio frequency band is between 2.4GHz and 2.5GHz. This frequency band also belongs to the license-free ISM (Industrial, Scientific and Medical) open that we have previously mentioned. frequency band. The module designed around this chip is our common nRF24L01 module. There are many types of such modules, such as nRF24L01 module, nRF24L01+ module, nRF24L01+ PA/LNA module.

They are actually similar, nRF24L01+ is an upgraded version of nRF24L01 chip. nRF24L01 only supports 1Mbps and 2Mbps transmission rate, while nRF24L01+ also supports 250Kbps transmission rate. The nRF24L01+ PA/LNA module is an external antenna signal module that integrates transceiver amplification on the basis of the nRF24L01+ module, which increases the transmission distance of the module. In an open environment, the maximum transmission distance of the nRF24L01/nRF24L01+ module using the on-board PCB antenna is only 100 meters, while the PA/LNA module can reach 1000 meters.

How nRF24L01/nRF24L01+ modules work

The nRF24L01/nRF24L01+ module transmits and receives on a specific frequency, which is called a channel. One or more modules must communicate with each other on the same frequency. So this frequency must be at any frequency between 2.4GHz and 2.5GHz, more precisely, it should be 2400MHz to 2525MHz. Since the channel bandwidth (bandwidth) occupied by each frequency is at most 1MHz, in the same range, if the bandwidth is 1MHz, theoretically 125 independent frequencies can be used.

The nRF24L01/nRF24L01+ module provides a native multi-transmit and one-receive function, that is, multiple senders can send to one receiver, but the maximum number of senders is 6. Each physical channel (Channel) is divided into 6 software logical data pipes (Data Pipes), each data pipe has its own configuration address.

The nRF24L01/nRF24L01+ module in the center can simultaneously receive messages from other 6 nRF24L01/nRF24L01+ modules, and can also stop receiving and become a sending module at any time to send messages to other modules, but the sending process cannot be simultaneous, only one data pipe at a time.

Enhanced ShockBurst protocol

When the nRF24L01/nRF24L01+ module communicates, the communication information follows a certain format, which is the ShockBurst protocol. The original ShockBurst protocol format has only Preamble, Address, Payload and CRC fields.

After nRF24L01+, the ShockBurst protocol is upgraded to an enhanced ShockBurst protocol. Added Packet Control field. Adding the Packet Control field has the following benefits:

1. The length of the Payload field can be described in the Packet Control field, and the length of each packet data can be described.

2. The ID tag of the package, that is, the Packet ID, is added to the PacketControl field, which is convenient for post-processing data.

3. It can be specified whether or not to return an acknowledgment character (ACK) to confirm whether the sent data packet is received.

When two nRF24L01/nRF24L01+ modules communicate, the sender will send packet data to the receiver with the enhanced ShockBurst protocol, and after receiving the packet, it will reply an acknowledgment character (ACK) to the sender, so that a normal sending process is completed.

Of course, there are two other situations that sometimes occur in this process:

1. If the data packet is lost during transmission, the receiver will not return an ACK if it is not received, and the sender will resend it after a period of time without waiting for the ACK.

2. When the data packet is sent, the receiver returns an ACK to the sender, but the ACK is lost. In the same way, the sender does not wait for the ACK to send it again after a period of time.