How To Modify Your Car Stereo For Bluetooth Or Aux-In

July 28, 2021 by Lewin Day 42 Comments

If you’re an automotive enthusiast of taste, you can’t stand the idea of fitting a janky aftermarket stereo into your nice, clean ride. Flashy, modern head units can spoil the look of a car’s interior, particularly if the car is a retro, classic, or vintage ride.

Thus, we’re going to look at how to modify your existing stock car stereo to accept an auxiliary cable input or even a Bluetooth module. This way, you can pump in the latest tunes from your smartphone without a fuss, while still maintaining an all-original look on the dash.

Fundamentals

A simple Bluetooth module designed for wiring into car audio systems. There are two wires for 12 V power from the vehicle, and the audio signal is sent out over the RCA plugs. The RCA plugs can be cut off and the module hard wired inside your stereo if you have room. Cutting off the plastic case can help too.

Depending on your choice of audio player, you may prefer a 3.5 mm aux jack, or you might want to go with Bluetooth audio if your smartphone no longer has a headphone port. Whichever way you go, the process of modifying the stereo is largely the same. To achieve your goal, you need to find a way of injecting the audio signal into the head unit’s amplifier stage, while making sure no other audio sources are getting sent there as well.

Whether that audio source is a 3.5 mm jack or a Bluetooth module doesn’t matter. The only difference is, in the latter case, you’ll want to buy a Bluetooth module and hardwire it in to the auxiliary input you create, while also splicing the module into the stereo’s power supply. In the case of a simple headphone jack input, you simply need to wire up an aux cord or 3.5 mm jack somewhere you can get to it, and call it done.

This guide won’t cover every stereo under the sun, of course. Edge cases exist and depending on the minute specifics of how your original car radio works, these exact methods may or may not work for you. However, this guide is intended to get you thinking conceptually about how such mods are done, so that you can investigate the hardware in front of you and make your own decisions about how to integrate an external audio input that suits your usage case. Continue reading “How To Modify Your Car Stereo For Bluetooth Or Aux-In” →

Digital Audio For Microcontrollers Doesn’t Come Much Simpler Than A WART

July 11, 2021 by Jenny List 11 Comments

Adding an audio channel to your microcontroller project can mean a pile of extra components and a ton of processing power, as a compressed stream must be retrieved and sent to a dedicated DAC. Or if you are [rdpoor], it can mean hooking up a low-pass filter to the UART that’s present on even the simplest of devices, and constructing a serial data stream that mimics PWM audio.

Sound on your microcontroller, it’s this simple!

WART is a Python script that converts a WAV file into a C formatted byte array that can be baked into your microcontroller code, and for which playback is as simple as streaming it to the UART. The example uses a Teensy and a transistor to drive a small speaker, we’re guessing that better quality might come with using a dedicated low-pass filter rather than relying on the speaker itself, but at least audio doesn’t come any simpler.

The code can be found in a GitHub repository and there’s a few recordings of the output in the files section Hackaday.io page, one is embedded below. It’s better than we might have expected given that the quality won’t be the best at the PWM data rate of even the fastest UART. But even if you won’t be incorporating it into your music system any time soon we can see it being a useful addition for such things as small warning sounds. Meanwhile if persuading serially driven speakers to talk is of interest, there’s always the venerable PC speaker.

Continue reading “Digital Audio For Microcontrollers Doesn’t Come Much Simpler Than A WART” →

PipeWire, The Newest Audio Kid On The Linux Block

June 23, 2021 by Jonathan Bennett 65 Comments

Raise your hand if you remember when PulseAudio was famous for breaking audio on Linux for everyone. For quite a few years, the standard answer for any audio problem on Linux was to uninstall PulseAudio, and just use ALSA. It’s probably the case that a number of distros switched to Pulse before it was quite ready. My experience was that after a couple years of fixing bugs, the experience got to be quite stable and useful. PulseAudio brought some really nice features to Linux, like moving sound streams between devices and dynamically resampling streams as needed.

Continue reading “PipeWire, The Newest Audio Kid On The Linux Block” →

DIY USB Microphone Seems Overkill; Is Surprisingly In-Depth

June 2, 2021 by Erin Pinheiro 4 Comments

Those of us who have been working from home through video calls for the past year can attest to the rising demand for conferencing gear such as webcams and microphones. Not wanting to spring for a boring off-the-shelf solution, serial hacker [Andy Brown] decided to design his own USB solution from scratch and show us the process from start to finish.

Deciding to go for a full digital design for the circuitry, the peripheral is based off of a MEMS microphone and an STM32 microcontroller doing the heavy lifting between it and a USB connection. [Andy] notes that MEMS microphones are very delicate and you have to design the PCB around the hole where the sound enters, which is why he went with a breakout board which has the component already soldered onto it.

As for the MCU, he reasons that since this is a off-one project which won’t be produced in large numbers, the 180 MHz ARM core shouldn’t be seen as overkill, since it also gives him more than plenty of headroom to do signal processing to make the sound clearer before sending it through to a computer by the USB audio device descriptor.

Once the components are chosen and the board designed, [Andy] goes into detail explaining the firmware he wrote for the STM32 to translate the PCM samples from the microphone’s I²S interface into a format better suited for the computer. He also describes how it then processes the audio, applying a graphic equalizer to reduce noise and then ST’s own Smart Volume Control filter, which works more like a compressor than a simple amplitude multiplication.

Finally, all files for the project, including board gerbers and the STM32 firmware are available at the bottom of his post, and to boot, a video demonstrating the project which you can check here after the break. [Andy]’s choice of microcontroller for this project is no surprise to us, given he’s already made his own development board for the STM32 G0 series. But if this digital microphone project is a bit too modern for you, why not try your hand at building a ribbon microphone instead?

Continue reading “DIY USB Microphone Seems Overkill; Is Surprisingly In-Depth” →

Gaming Headset Gets Simple Wireless Charging

May 17, 2021 by Tom Nardi 9 Comments

Despite the technology itself being widely available and relatively cheap, devices that offer wireless charging as a feature still aren’t as common as many would like. Sure it can’t deliver as much power as something like USB-C, but for low-draw devices that don’t necessarily need to be recharged in a hurry, the convenience is undeniable.

Sick of having to plug it in after each session, [Taylor Burley] decided to take matters into his own hands and add wireless charging capability to his Turtle Beach Recon 200 headset. But ultimately, there’s nothing about this project that couldn’t be adapted to your own particular headset of choice. Or any other device that charges via USB, for that matter.

To keep things simple, [Taylor] used an off-the-shelf wireless charging transmitter and receiver pair. The transmitter is housed in a 3D printed mount that the headset hangs from, and the receiver was simply glued to the top of the headset. The receiver is covered with a thin 3D printed plate, but a couple turns of electrical tape would work just as well if you didn’t want to design a whole new part.

Once everything was in place, he then ran a wire down the side of the headset and tapped into the five volt trace coming from the USB port. So now long as [Taylor] remembers to hang the headset up after he’s done playing, the battery will always be topped off the next time he reaches for it.

Considering how many projects we’ve seen that add wireless charging to consumer devices, it’s honestly kind of surprising that it’s still not a standard feature in 2021. Until manufacturers figure out what they want to do with the technology, it seems like hackers will just have to keep doing it themselves.

Continue reading “Gaming Headset Gets Simple Wireless Charging” →

Using Ikea Guts To Add Sonos Compatibility To A Vintage Speaker

May 15, 2021 by Jenny List 8 Comments

We’re in a fortunate position when it comes to audio gear, because advances in amplifier and signal processing technology have delivered us budget devices that produce a sound that’s excellent in comparison to those of a few years ago. That said, a decent quality device is good whichever decade it was manufactured in, and a speaker from the 1960s can be coaxed into life and sound excellent with a modern amplifier. It’s something [Sebastius] has explored, as he picked up an attractive-looking set of Swedish speakers from the 1960s. Wanting to bring them into the 21st century, he’s upgraded them for Sonos compatibility by hacking in the guts of an IKEA Symfonisk bookshelf speaker.

The speakers themselves looked good enough, but on closer examination they proved to bear the scars of many decades. After testing new wiring and drivers they still had a good sound to them. Their passive crossover meant that hooking them up to a single amplifier is as straightforward as it was decades ago, but a Symfonisk has an active crossover and two amplifiers. Fortunately there’s a neat hack by which those two amplifiers can be combined as one, and this is what he’s done with the resulting Symfonisk electronic package mounted on the reverse of the speaker.

The fate of the original speaker’s broken mid-range and tweeter drivers was a common enough one back in the day as speakers were ill-matched to amplifiers. Too small an amp would need turning up in volume to get a good sound resulting in distortion that would burn out the top end drivers, while too much power would result in the bass drivers being overloaded and failing. It’s unclear whether the drivers in a vintage speaker would be well-matched to an amplifier such as the Symfonisk, but we’re guessing they are safe while run at sensible volumes. Perhaps of more interest is whatever on-board DSP a Symfonisk contains, because while vintage speakers were designed for as flat a response as possible, modern compact speakers use DSP to equalise the frequency and phase responses of otherwise not-very-good-sounding enclosures. If the Symfonisk does this then those adjustments will appear as distortion in the sound of a different cabinet, but the question remains whether that distortion will be significant enough to be detectable by ear.

If the Symfonisk catches your attention, we’ve covered a teardown of it in the past.

Otters Deliver A High Power Stationary Audio Experience

May 12, 2021 by Kerry Scharfglass 20 Comments

Our favorite raft of otters is back at it again with another display of open source audio prowess as they bring us the OtterCastAmp, the newest member of the OtterCast family of open source audio multitools. If you looked at the previous entry in the series – the OtterCastAudio – and thought it was nice but lacking in the pixel count or output power departments then this is the device for you.

The Amp is fundamentally a very similar device to the OtterCastAudio. It shares the same Allwinner S3 Cortex-A application processor and runs the same embedded Linux build assembled with Buildroot. In turn it offers the same substantial set of features and audio protocol support. It can be targeted by Snapcast, Spotify Connect or AirPlay if those are your tools of choice, or act as a generic PulseAudio sink for your Linux audio needs. And there’s still a separate line in so it source audio as well.

One look at the chassis and it’s clear that unlike the OtterCastAudio this is not a simple Chromecast Audio replacement. The face of the OtterCastAmp is graced by a luscious 340×800 LCD for all the cover art your listening ear can enjoy. And the raft of connectors in the back (and mountain of inductors on the PCBA) make it clear that this is a fully fledged class D amplifier, driving up to 120W of power across four channels. Though it may drive a theoretical 30W or 60W peak across its various outputs, with a maximum supply power of 100W (via USB-C power delivery, naturally) the true maximum output will be a little lower. Rounding out the feature set is an Ethernet jack and some wonderfully designed copper PCB otters to enjoy inside and out.

As before, it looks like this design is very close to ready for prime time but not quite there yet, so order at your own risk. Full fab files and some hints are linked in the repo mentioned above. If home fabrication is a little much it looks like there might be a small manufacturing run of these devices coming soon.