Fail Of The Week: The Arduino Walkie That Won’t Talkie

There’s something seriously wrong with the Arduino walkie-talkie that [GreatScott!] built.

The idea is simple: build a wireless intercom so a group of motor scooter riders can talk in real-time. Yes, such products exist commercially, but that’s no fun at all. With a little ingenuity and a well-stocked parts bin, such a device should be easy to build on the cheap, right?

Apparently not. [GreatScott!] went with an Arduino-based design, partly due to familiarity with the microcontroller but also because it made the RF part of the project seemingly easier due to cheap and easily available nRF24 2.4 GHz audio streaming modules. Everything seems straightforward enough on the breadboard – an op-amp to boost the signal from the condenser mic, a somewhat low but presumably usable 16 kHz sampling rate for the ADC. The radio modules linked up, but the audio quality was heavily distorted.

[GreatScott!] assumed that the rat’s nest of jumpers on the breadboard was to blame, so he jumped right to a PCB build. It’s a logical step, but it seems like it might be where he went wrong, because the PCB version was even worse. We’d perhaps have isolated the issue with the breadboard circuit first; did the distortion come from the audio stage? Or perhaps did the digitization inject some distortion? Or could the distortion be coming from the RF stage? We’d want to answer a few questions like that before jumping to a final design.

We love that [GreatScott!] has no issue with posting his failures – we’ve covered his suboptimal CPU handwarmer, and his 3D-printed BLDC motor stator was a flop too. It’s always nice to post mortem these things to avoid a similar fate.

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DIY Six Channel Arduino RC Transmitter

It’s wasn’t so long ago that RC transmitters, at least ones worth owning, were expensive pieces of gear. Even more recently than that, the idea of an RC transmitter running an open source firmware would have been considered a pipe dream. Yet today buying cheap imported transmitters and flashing a community developed firmware (if it didn’t come with it pre-installed to begin with) is common place. It’s not much of a stretch to say we’re currently in the “Golden Age” of hobby RC transmitters.

But what if even cheap hardware running customizable software isn’t enough? What if you want to take it to the next level? In that case, [Electronoobs] has an Arduino powered RC transmitter with your name on it. But this is no scrap of protoboard with a couple of cheap joysticks on it, though he has made one of those too. The goal of this build was for it to look and perform as professional as possible while remaining within the hobbyist’s capabilities. The final product probably won’t be winning any design awards, but it’s still an impressive demonstration of what the individual hacker and maker can pull off today with the incredible technology we have access to.

So what goes into this homebrew radio control system? Inside the back panel [Electronoobs] mounted the batteries, charging module, and the voltage regulator which steps the battery voltage down to the 3.3 V required to drive the rest of the transmitter’s electronics. On the flip side there’s an Arduino Nano, an NRF24 module, and an OLED display. Finally we have an assortment of switches, buttons, potentiometers, and two very nice looking JH-D202X-R2 joysticks for user input.

As you might have guessed, building your own transmitter means building your own receiver as well. Unfortunately you won’t be able to bind your existing RC vehicles to this radio, but since the receiver side is no more complicated than another Arduino Nano and NRF24 module, it shouldn’t be hard to adapt them if you were so inclined.

Low-cost consumer RC transmitters can be something of a mixed bag. There are some surprisingly decent options out there, but it’s not a huge surprise that hackers are interested in just spinning up their own versions either.
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Retro Wall Phone Becomes A Doorbell, And So Much More

We have to admit that this retasked retro phone wins on style points alone. The fact that it’s filled with so much functionality is icing on the cake.

The way [SuperKris] describes his build sounds like a classic case of feature creep. Version 1 was to be a simple doorbell, but [SuperKris] would soon learn that one does not simply replace an existing bell with a phone and get results. He did some research and found that the ringer inside the bakelite beauty needs much more voltage than the standard doorbell transformer supplies, so he designed a little H-bridge circuit to drive the solenoids. A few rounds of “while I’m at it” later, the phone was stuffed with electronics, including an Arduino and an NFR24 radio module that lets it connect to Domoticz, a home automation system. The phone’s rotary dial can now control up to 10 events and respond to alarms and alerts with different ring patterns. And, oh yes – it’s a doorbell too.

In general, we prefer to see old equipment restored rather than gutted and filled with new electronics. But we can certainly get behind any effort to retask old phones with no real place in modern telecommunications. We’ve seen a few of these before, like this desk telephone that can make cell calls.

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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+?

Repurpose A Classroom Clicker For Great Justice

If you’ve been in a university class of a certain size, with a professor who wants to get live feedback from the students, you’ve probably been forced to buy a Turning Point “clicker”. Aside from the ridiculousness of making students pay for their professor’s instructional aides (do the make you pay extra for the chalk too?!?!) these clickers are a gauntlet thrown down to any right-minded hacker because they supposedly contain secrets.

[Nick] had one of these gadgets, and hopped right up on the shoulders of giants to turn it into a remote control that interfaces with his computer and drives a synthesizer, so he can work through the chord changes by clicking. His two references, to [Travis Goodspeed]’s nRF promiscuity hack and to [Taylor Killian]’s Arduino library for the clickers are a testament to why we need both reverse engineers doing the hard work and people who’ll wrap up the hard work in an easy-to-use library.

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Control Anything With A Universal Wireless Remote

If you aren’t already living on the spacecraft Discovery One, you may not have HAL listening to your every voice command. If that’s the case for you, as it is for us, you may have to resort to mashing buttons on little black monoliths like a primitive monkey. [Barnr]’s universal remote project, and some black PLA filament, will get you there in no time.

2001_obeliskThe remote is based on a nRF24 radios with a PIC to read the button presses. A Raspberry Pi and another nRF24 are listening on the other end. The code that runs either side of the connection is so minimal that both sides fit in the project description. It gets the job done, and it’s easily hackable. And with that, [barnr] can control anything that he can connect up to the Pi without getting up from his campfire.

While [barnr] is shy about his 3D design skills, we think that the box is fantastic. It’s got 3D-printed keycaps for the tactile switches that sit inside, and it’s an easily printed case. Maybe it’s a little blocky and, frankly monolithic, but it gets the job done. Aesthetics are for version 2.0.

When you build something yourself, and it’s not a HAL 9000, you pretty much need a way to control it. It’s no wonder we’ve seen so many projects on Hackaday. If your 2.4 GHz spectrum is too crowded to run a nRF24 remote, you might consider infrared: tiny, tiny, infrared. Or if you want to see the craziest remote that we’ve ever seen, check out this DTMF-over-cellphone build. But if you just want something sweet and minimal that gets the job done, [barnr]’s build is for you.

Thanks [Mikejand] for the tip!

Hackaday Prize Entry: BLE Beacon Library

While faking BLE advertising beacons using an nRF24L01+ module is nothing new, it’s become a heck of a lot easier now that [Pranav Gulati] has written some library code and a few examples for it.

[Pranav]’s work is based on [Dmitry Grinberg]’s epic bit-banging BLE research that we featured way back in 2013. And while the advertisement channel in BLE is limited in the amount of data it can send, a $1 nRF24 module and a power-thrifty microcontroller would be great for a battery-powered device that needs to send small amount of data infrequently for a really long time.

We’re not 100% sure where [Pranav] is going to take this project. Honestly, the library looks like it’s ready to use right now. If you’ve been holding off on making your own BLE-enabled flock of birds, or even if you just want to mess around with the protocol, your life has gotten a lot easier.

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