First contact with nRF2401A/nRF24L01/nRF24L01+ wireless module

      As the saying goes: Everyone is born knowing everything, and they have learned everything through their own efforts and exploration. When I first started to tinker with the NRF series chips, I was curious and interested. When I first started to work on hardware and software, I was so confused about sending and receiving data that my head almost exploded. So I would like to share the experience of my predecessors with you, hoping that you will avoid detours.

Q: When I was selecting a model recently, I found that most common wireless modules are powered by 3V, but the microcontroller I use is 5V. How should they be connected? Will direct connection damage the module?

      Answer: If the P0 port of the 51 microcontroller you are using is a high-impedance pin, you can directly connect the IO pin of the wireless module to the P0 port, and place a bias resistor of about 1K~10K between the corresponding connection and the 3V power supply.
 

If the microcontroller does not have a high-impedance pin (AVR microcontroller and some models of STC microcontroller, etc.), the above method is not applicable.

nRF24L01+ can withstand an input voltage of 5V. Directly connecting it to the IO pin of the microcontroller will not burn out the module. However, the output end of the wireless module can only output a maximum voltage of about 3V. Please pay attention to whether the voltage value can be correctly recognized by the microcontroller.

 

Q: Can the wireless module be directly connected to the serial port and communicate? I want to directly connect the nRF24L01+ module to the serial port circuit. Is this possible?

      Answer: No, the wireless module does not provide a serial interface. If you need to connect and communicate with a computer or other device through a serial port, please use a single-chip microcomputer as the communication control core, receive the data sent by the computer serial port and transmit it to the wireless module, and then send it. After the wireless module at the other end receives the data, the single-chip microcomputer reads the data and sends it to the computer serial port.
 

Q: What are the factors that affect the transmission distance of wireless modules?

Why can't the transmission distance of the nRF2401 wireless module be extended? Now it is only about 2 meters, and the output power is already the highest 0dBm.

        Answer: Haha, this should be the most common question for beginners of wireless modules. Transmission distance should be the most concerned thing for everyone. Although this is an intuitive value, there are many factors that affect the communication distance. Antenna performance (directivity, gain, standing wave ratio), wireless module performance indicators (transmitting power, receiving sensitivity, network matching, frequency parameter consistency), wireless module working mode (data transmission rate) and use environment factors, etc. Therefore, the communication distance should be an indicator to test the comprehensive performance of a wireless product. In order to achieve the ideal distance, you should choose an antenna with high gain and low standing wave ratio. If necessary, you can use a directional antenna (some modules are PCB antennas, which should be a poor performance method, but have advantages in close distance and miniaturization); choose a high-quality wireless module. A good wireless module should have an excellent matching network to minimize the loss of the transmitting and receiving signals. At the same time, it should also have indicators such as accurate working frequency and good consistency; finally, in the selection of transmission rate, on the premise of being able to meet the communication needs, giving priority to a low transmission rate can also effectively increase the transmission distance.
 

Q: What does it mean that nRF2401A supports dual-channel communication?
 

I saw in the documentation that NRF2401 has two data channels. What does this mean? Does it mean that 2401 can send and receive on two channels at the same time, or does it mean that 2401 can only communicate between two modules?

       Answer: This understanding is wrong. The two data channels of nRF2401A mean that it can receive data on two channels at the same time, but can only use one channel when sending. Therefore, it is not possible to complete reception and transmission on two channels at the same time. At the same time, the nRF2401A wireless module belongs to the half-duplex working mode, and can only work in one mode of sending or receiving at the same time.
 

In addition, the nRF2401A module is not limited to communicating between two modules. As long as the working mode configuration of the wireless modules is consistent (same address code, channel number, transmission rate, data packet length, CRC mode, etc.), one-to-one, one-to-many, and many-to-many communication modes can be completed.

Q: What does the 6 channels of nRF24L01 and nRF24L01+ wireless modules mean?
 

I have been studying the channel relationship of nRF24L01 but have not gained much. I would like to ask what 6 channels mean and what is the relationship between them?

       Answer: The nRF24L01+ module has 6 data channels inside. When using different data channels to send data, they all work at the same frequency. They are distinguished by address codes. So you can understand that an nRF24L01 can have 6 address codes at the same time. When receiving, the module will automatically identify the address code and set it in the corresponding register to inform the user which channel received the data.
 

Using the data channel of nRF24L01+ can greatly increase the flexibility of use and operation in networks with less than or equal to 6 nodes. In networks with more than 6 nodes, users can add additional identification data to the communication data to distinguish different nodes.