Quick Questions About nRF24L01+ Chip

[DNakazawa]

Hello, 

I have two quick questions about the nRF24L01+ chip that I wasn't able to find from reading its datasheet. 

1. Is the chip pre-programmed by Nordic or does it need to be configured manually?

2. What are the min. and max. values of the frequency the nRF24L01+ can run on? The datasheet indicates a single value of 16MHz but I want to design my own PCB and pick a different x-tal oscillator, if possible. 

Thank you all for your time!

[ovrebekk]

Hi 

1. Not sure what you mean about 'pre programmed'. There is no MCU in the nRF24L01+, and all the functionality described in the datasheet is hard coded. 

The various configuration registers will all be set to their reset values when you power up the chip, as detailed in the datasheet. 

At a minimum you need to write to the CONFIG register in order to set the PWR_UP bit, and to choose between PTX or PRX mode, if you want to use the device. All other configuration registers can generally be left at their default values, even if there is a higher chance of interference from other devices if you use default settings. 

2. There are no options for the crystal other than 16MHz, this is what the device has been designed for. 

Still, you can use a 16MHz crystal from a different vendor as long as you follow their guidelines in terms of decoupling caps etc. 

Best regards
Torbjørn

[DNakazawa]

Hello, 

Thank you for the response. 

1. In hindsight, it makes a lot of sense that it's not "pre-programmed", I was thinking in terms of MCUs since I work with them a lot more often. 

2. So can I run the SPI of an MCU using an 8MHz external x-tal oscillator and keep the default x-tal oscillator used on most RF circuit boards using the nRF24L01+? I guess in essence what I'm asking is can the MCU interfacing with the nRF24L01+ chip be at a different (but more specifically, a lower) clock frequency?

3. Also, If the nRF24L01+ chip is used on a circuit board without a PA/LNA but with an SMA antenna with 50 Ohm impedance, do you know what's the maximum reliable transmission range I can achieve? 

Thanks in advance for your time. 

[ovrebekk]

Hi 

1. Understandable. The nRF24L01+ was the last chip we made without a dedicated application MCU, so it's not something we are much into either ;)

2. The SPI master (your MCU) controls the SPI clock. As long as you stay below 10MHz you are free to choose whatever clock speed you want. 

Just make sure they run at the same voltage.

3. It is always hard to estimate range when using 2.4GHz radios, since they are highly affected by objects containing metal or water (including human bodies). 

You are also susceptible to interference from other radios in the same band, such as WiFi networks.  

For optimal range you should use the 250kbps mode in the radio. Then you should be able to go up to 200m or more line of sight, and around 30-50m in a typical indoor scenario. 

Best regards
Torbjørn