Faking Bluetooth LE With An NRF24L01+ Module

Despite the name, Bluetooth Low Energy (BLE) has very little to do with the original Bluetooth, other than its use of the same 2.4 GHz frequencies. This is where [Dmitry] got the idea to use a 2.4 GHz nRF24L01+ module to implement his very own BLE device, without the typical BLE chipset. This should be easy, since this popular IC supports GFSK modulation, 1 MHz channels and the 1 MBit data rate of BLE.

Despite of how simple BLE seems to implement, [Dmitry] quickly came across a range of issues due to limitations of the nRF24L01+. These include no support for a 24-bit CRC, a too sluggish PLL cycling for BLE’s frequency hopping, and as the coup de grâce, a lack for incoming data packets larger than 32 bytes — which destroyed any hope of accepting incoming connections.

Unperturbed, [Dmitry] set to work implementing what would work on this IC: broadcasting BLE packets. In the article he covers the entire code (in C) that allows the nRF24L01+ to send broadcast packets and any BLE-supporting device that’s listening to receive them. Admittedly not as useful as having a fully functional BLE stack, but good enough for broadcasting something like sensor data. It also raises the question of which alternative released in the intervening decade to the venerable nRF24L01+ might fill in the missing features, without making a dedicated BLE IC (or ESP32 variant) look more cost-effective.

It’s always a good day when a new project from [Dmitry] hits the tip line. We’ve previously covered his impressive efforts to add more RAM to the RP2040, and his business card that can boot Linux on an ATSAMD21.

Sending MIDI Wirelessly With The NRF24L01

MIDI is a standard known by musicians and instruments all over the world. The basic twist on regular serial has helped studios around the world to work more efficiently. [Kevin] wanted to try sending MIDI data wirelessly, but rather than the typical Bluetooth solution, decided to use the humble nRF24L01 instead.

The circuitry used is simple: [Kevin] simply wired up two Arduino Unos with nRF24L01 radio modules, which communicate over SPI. Alternatively, an even quicker solution is to use a Keywish Arduino RF Nano, which packs a nRF24L01 on board. One Arduino can then be hooked up to a MIDI OUT port on an instrument, and it will send out MIDI signals wirelessly. The second Arduino can then be plugged into a MIDI IN port and repeat out what it receives over the air.

The real work was in the firmware, which takes MIDI data and packages it in a suitable form to send out over the nRF24L01. The system can operate in a one-to-one mode, emulating a single MIDI cable, or a multicast mode, where one sender transmits information to many receivers.

It’s a neat hack and one we could imagine would be useful in some fun performance situations. We’ve seen others do work on wireless MIDI interfaces for Eurorack hardware, too. Video after the break.

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Fixing NRF24L01+ Modules Without Going (Too) Insane

Good old nRF24L01+ wireless modules are inexpensive and effective. Well, they are as long as they work correctly, anyway. The devices themselves are mature and well-understood, but that doesn’t mean bad batches from suppliers can’t cause hair-pulling problems straight from the factory.

[nekromant] recently got a whole batch of units that simply refused to perform as they should, but not because they were counterfeits. The problem was that the antenna and PCB design had been “optimized” by the supplier to the point where the devices simply couldn’t work properly. Fortunately, [nekromant] leveraged an understanding of the problem into a way to fix them without going insane in the process. The test setup is shown in the image above, and the process is explained below. Continue reading “Fixing NRF24L01+ Modules Without Going (Too) Insane”

Nerfnet Tunnels TCP/IP Over NRF24L01 Radios

There’s an excellent chance you’ve already worked with the nRF24L01. These little modules are an easy and cheap way to shuffle data across a 2.4 GHz radio link at a respectable rate, making them great for remote control projects. But after seeing that others had experimenting with using these radios to transmit digital audio, [Andrew Rossignol] got to wondering if some software trickery could push the envelope even further.

The result is nerfnet, a Linux program that allows you to tunnel TCP/IP over a pair of nRF24L01 modules. The link appears as a virtual interface, meaning everything happens transparently as far as other programs are concerned. Anything that uses TCP/IP to communicate on Linux can take advantage of this low-cost link, albeit at speeds that most of us haven’t had to deal with in decades.

Though it’s not quite as bad as you might think. Latency is around 50 ms, and after some tweaks, [Andrew] has been able to squeeze almost 300 Kbps out of the link. That’s more than enough for terminal work, and some light audio and video streaming isn’t out of the question.

In terms of range, he was able to maintain a fairly reliable connection at a distance of up to 60 meters (200 feet) outdoors. It might not sound like much, but again, you’ve got to take the cost of these radios into account. If you’re looking to SSH into a Raspberry Pi weather station you’ve got in the backyard, a pair of these could get the job done for just a couple of bucks.

The blog post [Andrew] has put together explains the software in fantastic detail if you’re interested in the nuts and bolts of it all. But if you just want to play around with the idea, you just need to connect some nRF24L01 modules to a pair of Raspberry Pis with short SPI wires to cut down any interference, and follow the instructions. Ideally the radios would have external antennas, but it’s not strictly required.

We’ve seen these modules pushed into service as impromptu Bluetooth Low Energy transmitters in the past, but nothing quite like this. While the latency and bandwidth offered by this technique might seem antiquated to modern eyes, it could be the perfect dedicated communication channel for your sensors, smart devices, or home automation projects.

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Ask Hackaday: Frequency Hopping On The NRF24l01+?

We’ve seen a lot of hacks with the nRF24l01+ 2.4 GHz radio modules. The tiny chips pack a lot of bang for the buck. Since the radios can switch frequencies relatively quickly, [Shubham Paul] decided to take advantage of this feature to make a rudimentary frequency-hopping communications channel.

The code is actually incredibly simple. Both the transmitter and receiver simply scan up and down over the defined channels. Because the clock speeds of any given pair of Arduinos are likely to be slightly different, it’s not a surprise that the radios eventually drift out of sync. Right now, as a quickie solution, [Shubham] is using a serial-port resynchronization: both are connected to the same computer, and he just tells them to get on the same channel. That’s not a horribly satisfying workaround. (But it’s a great start!)

Keeping two radios that are continually swapping channels in sync is no easy task, but it could possibly be made easier by taking advantage of the nRF’s acknowledge mode. If the delay between a sent acknowledge message and a received one were constant, these events (one on TX and one on RX) could be used to re-sync the two hopping cycles. All of this would probably require more temporal resolution than you’re going to get out of a microprocessor running Arduino code, but should be possible using hardware timers. But this is pure speculation. We briefly looked around and couldn’t find any working demos.

So Hackaday, how would you remotely sync two nRF24s on the cheap? Or is this a crazy idea? It might help to make transmissions more reliable in the face of 2.4 GHz band interference. Has anyone implemented their own frequency hopping scheme for the nRF24l01+?

Fixing The Terrible Range Of Your Cheap NRF24L01+ PA/LNA Module

nRF24L01+ PA/LNA module specs look great on paper. Wireless communication up to 1000m in a small package readily available from a variety of cheap sources in China? The hard work of software connectivity already done by a variety of open source projects? Sounds great! But if you mashed BUY and are getting maybe 1% of that range, don’t worry because thanks to these clear directions, they can be fixed.

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Hacking A NRF24L01 Radio For Longer Range

[RonM9] wasn’t happy with his 50 foot range on his NRF24L01 project. The RF had to cut through four walls, but with the stock modules, the signal was petering out after two or three walls.  A reasonably simple external dipole antenna managed to increase the range enough to do the job.

[RonM9’s] instructions show where to cut away the existing PCB antenna and empirically tune the 24 gauge wire for best performance. He even includes an Arduino-based test rig so you can perform your own testing if you want.

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