bluetooth

575 Articles

The Android Linux Commander

September 9, 2025 by 7 Comments

Last time, I described how to write a simple Android app and get it talking to your code on Linux. So, of course, we need an example. Since I’ve been on something of a macropad kick lately, I decided to write a toolkit for building your own macropad using App Inventor and any sort of Linux tools you like.

I mentioned there is a server. I wrote some very basic code to exchange data with the Android device on the Linux side. The protocol is simple:

  • All messages to the ordinary Linux start with >
  • All messages to the Android device start with <
  • All messages end with a carriage return

Security

You can build the server so that it can execute arbitrary commands. Since some people will doubtlessly be upset about that, the server can also have a restrictive set of numbered commands. You can also allow those commands to take arguments or disallow them, but you have to rebuild the server with your options set.

There is a handshake at the start of communications where Android sends “>.” and the server responds “<.” to allow synchronization and any resetting to occur. Sending “>#x” runs a numbered command (where x is an integer) which could have arguments like “>#20~/todo.txt” for example, or, with no arguments, “>#20” if you just want to run the command.

If the server allows it, you can also just send an entire command line using “>>” as in: “>>vi ~/todo.txt” to start a vi session.

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A photo of the PCB from the charging case

Anker Soundcore Space A40 Earbuds Teardown

September 7, 2025 by 3 Comments

Wireless earbuds are notoriously tiny. Want to see inside? [MCH170] did and published a Soundcore Space A40 Teardown.

In this teardown, you’ll see inside the charging case and one of the earbuds. Starting with the case, removing the back cover revealed the charging coil and a few screws holding the PCB in place. Removing the screws allows for removing the coil. The main PCB and the magnets that hold the earbuds in place are then visible. The microcontroller is an SS881Q from Sinhmicro. The back side of the main circuit board has a handful of SMD components, including some status LEDs. The battery is a 13450 with a nominal voltage of 3.72V and a capacity of 800mAh or 2.967Wh.

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The Android Bluetooth Connection

August 27, 2025 by 14 Comments

Suppose someone came to talk to you and said, “I need your help. I have a Raspberry Pi-based robot and I want to develop a custom Android app to control it.” If you are like me, you’ll think about having to get the Android developer tools updated, and you’ll wonder if you remember exactly how to sign a manifest. Not an appealing thought. Sure, you can buy things off the shelf that make it easier, but then it isn’t custom, and you have to accept how it works. But it turns out that for simple things, you can use an old Google Labs project that is, surprisingly, still active and works well: MIT’s App Inventor — which, unfortunately, should have the acronym AI, but I’ll just call it Inventor to avoid confusion.

What’s Inventor? It lives in your browser. You lay out a fake phone screen using drag and drop, much like you’d use QT Designer or Visual Basic. You can switch views and attach actions using a block language sort of like Scratch. You can debug in an emulator or on your live phone wirelessly. Then, when you are ready, you can drop an APK file ready for people to download. Do you prefer an iPhone? There’s some support for it, although that’s not as mature. In particular, it appears that you can’t easily share an iPhone app with others.

Is it perfect? No, there are some quirks. But it works well and, with a little patience, can make amazingly good apps. Are they as efficient as some handcrafted masterpiece? Probably not. Does it matter? Probably not. I think it gets a bad rep because of the colorful blocks. Surely it’s made for kids. Well, honestly, it is. But it does a fine job, and just like TinkerCad or Lego, it is simple enough for kids, but you can use it to do some pretty amazing things.

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Bad To The Bluetooth: You Shouldn’t Use This Jammer

August 21, 2025 by 12 Comments

Back in the day, an FM bug was a handy way to make someone’s annoying radio go away, particularly if it could be induced to feedback. But these days you’re far more likely to hear somebody’s Bluetooth device blasting than you are an unruly FM radio.

To combat this aural menace, [Tixlegeek] is here with a jammer for the 2.4 GHz spectrum to make annoying Bluetooth devices go silent. While it’s not entirely effective, it’s still of interest for its unashamed jankiness. Besides, you really shouldn’t be using one of these anyway, so it doesn’t really matter how well it works.

Raiding the AliExpress 2.4 GHz parts bin, there’s a set of NRF24L01+ modules that jump around all over the band, a couple of extremely sketchy-looking power amplifiers, and a pair of Yagi antennas. It’s not even remotely legal, and we particularly like the sentence “After running the numbers, I realized it would be cheaper and far more effective to just throw a rock at [the Bluetooth speaker]“. If there’s a lesson here, perhaps it is that effective jamming comes in disrupting the information flow rather than drowning it out.

This project may be illegal, but unlike some others we think it (probably) won’t kill you.

[Ben] at workbench with 3D-printed sea scooter

Watertight And Wireless In One Go: The DIY Sea Scooter

August 11, 2025 by 26 Comments

To every gadget, tool, or toy, you can reasonably think: ‘Sure I could buy this… but can I make it myself?’ And that’s where [Ben] decided he could, and got to work. On a sea scooter, to be exact.

This sea scooter was to be a fully waterproof, hermetically sealed 3D-printed underwater personal propulsion device, with the extreme constraint that the entire hull and mechanical interfaces are printed in one go. No post-printing holes for shafts, connectors, or seals. It also meant [Ben] needed to embed all electronics, motor, magnetic gearbox, custom battery pack, wireless charging, and non-contact magnetic control system inside the print during the actual print process.

As [Ben] explains, both Bluetooth and WiFi ranges are laughable once underwater. He elegantly solves this with a reed-switch-based magnetic control system. The non-contact magnetic drive avoids shaft penetrations entirely. Power comes from a custom 8S LiFePO₄ pack, charged wirelessly through the hull. Lastly, everything’s wrapped in epoxy to make it as watertight as a real submarine.

The whole trick of ‘print-in-place’ is that [Ben] pauses the builder mid-print, and drops in each subsystem like a secret ingredient. Continuing, he tweaks the printer’s Z-offset, and onwards it goes. It’s tense, high-stakes work; a 14-hour print where one nozzle crash means binning hundreds of dollars’ worth of embedded components.

Still, [Ben] took the chance, and delivered a cool, fully packed and fully working sea scooter. Comment below to discuss the possibilities of building one yourself.

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When Wireless MIDI Has Latency, A Hardwired Solution Saves The Day

June 7, 2025 by 14 Comments

[Moby Pixel] wanted to build a fun MIDI controller. In the end, he didn’t build it just once, but twice—with the aim of finding out which microcontroller was most fit for this musical purpose. Pitted against each other? The ESP32 and Raspberry Pi Pico.

The MIDI controller itself is quite fetching. It’s built with a 4 x 4 array of arcade buttons to act as triggers for MIDI notes or events. They’re assembled in a nice wooden case with a lovely graphic wrap on it. The buttons themselves are wired to a microcontroller, which is then responsible for sending MIDI data to other devices.

At this point, the project diverges. Originally, [Moby Pixel] set the device up to work with an ESP32 using wireless MIDI over Bluetooth. However, he soon found a problem. Musical performance is all about timing, and the ESP32 setup was struggling with intermittent latency spikes that would ruin the performance. Enter the Raspberry Pi Pico using MIDI over USB. The hardwired solution eliminated the latency problems and made the controller far more satisfying to use.

There may be solutions to the latency issue with the wireless ESP32 setup, be they in code, hardware configuration, or otherwise. But if you want to play with the most accuracy and the minimum fuss, you’ll probably prefer the hardwired setup.

Latency is a vibe killer in music as we’ve explored previously.

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The Brymen BM788BT shown along side other digital multimeters.

New Brymen Bluetooth BM788BT Digital Multimeter Coming Soon

April 15, 2025 by 14 Comments

If you’re into electronics you can never have too many digital multimeters (DMMs). They all have different features, and if you want to make multiple measurements simultaneously, it can pay to have a few. Over on his video blog [joe smith] reviews the new Brymen BM788BT, which is a new entry into the Bluetooth logging meter category.

This is a two-part series: in the first he runs the meter through its measurement paces, and in the second he looks at the Bluetooth software interface. And when we say “new” meter, we mean brand new, this is a review unit that you can’t yet get in stores.

According to a post on the EEVblog, this Bluetooth variant was promised five years ago, and back then Brymen even had the Bluetooth module pin header on the PCB, but it has taken a long time to get the feature right. If you scroll through the thread you will find that Brymen has made its protocol specification available for the BM780 series meters.

It looks like some Bluetooth hacking might be required to get the best out of this meter. Of course we’re no strangers to hacking DMMs around here. We’ve taken on the Fluke 77 for example, and these DMM tweezers.

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