NRF24L01 Transceiver Modules – Richard Wilkinson

Tests on the basic NRF24L01, 2.4GHz

After buying a pair of these devices I had the usual problems with the PSU and shielding.

I decided to power the module from 5 volts which also powered the Arduino Nano.

The 5v was regulated down to 3.3v and 100uF tantalum caps were added for decoupling.

A standard sketch which sent a message between the 2 modules, was downloaded on each Nano. I made a slight change by using one of the nano’s pins to identify whether it was a transmitter or receiver. Also I connected an LED that indicated if the message had been received without error. They worked fine at low powers (-18,-16,-8dBm) but when I tried 0dBm they stopped working. I made an RF shield from a piece of aluminium foil sandwiched between 2 pieces of card. This went under the nano, NRF and 3v regulator, this worked well.

Range tests:

The transmitter was placed about 20m above the ground and I walked away with the receiver until I lost the signal. With the NRF set to 0dBm I was able to get about 450m.

This was further than I had expected and I started to think how far I could get with the NRF24L01 + PA + LNA + rubber duck antenna. This time I used Arduino Pro Minis to drive the NRFs.

I had the same problems with RF shielding but this time I had to wrap the NRF in insulated aluminium foil, this worked up to +15dBm but +20dBm failed! In the end I made 2 aluminium boxes and connected a piece of braid from the box to the NRF, finally this worked.

To actually see the message I connected a FTDI serial interface to the ProMini then to a tablet via an OTG cable. Our highest hill in Shropshire is the Wrekin at 407m. I spent some time using various apps to see if I could get line of sight to the hill. I was looking for about 5km but found one of our friends had line of sight at a distance of 7.02km.

I set the transmitter up at our friends on a 2m pole and powered it with a small 5v PSU.

I set off to the Wrekin and when I got to the top I put the receiver on a 2m pole and connected it to the tablet using ‘Serial USB Terminal’ to my amazement it worked first time and I could see the string of characters being sent. The data was 100% and I did not notice any retransmissions. The path loss at 2.4GHz between the points is about 116dB.

The only failure was taking a screen shot of the data on the tablet, fortunately I did get a pic on my phone but not of very good quality. So I wonder how far they will go…