Down the Rabbit Hole and Back Out Again: Serial Over Headphone Jack

[ttsiodras] tells an epic tale of getting a custom Debian kernel installed on an Asus MemoPAD (ME103K) tablet. Skipping to the end of the saga, he discovers what looks like serial data coming out on the headphone jack when the system boots, but the signal was so distorted that he couldn’t simply interpret it. The solution turns out to be attaching a level-converter chip.


A level converter is a non-inverting amplifier, usually with a Schmitt trigger for immunity against noise. In this case, it acts like a “binarizer” — outputting a high voltage when the input rises above a threshold, and a low when it drops below. It’s the right part when you need to clean up a messy digital signal, and in this case works just fine because the capacitive distortion effects slow down both the leading and trailing edges of the signal, keeping the serial data’s timing intact.

That was the spoiler. If you want to read up on putting a custom Linux on an Android device, check out [ttsiodras]’s first post where he backs the machine up, and the second where he gets his custom kernel up and running. If you’re ever faced with an Android tablet that hasn’t been owned yet, or if you just have a DIY streak, this should help you get started.

Using the audio jack for serial is actually not uncommon, and discovering a serial terminal that listens at boot time is our favorite way to wedge a Linux OS into odd devices. So when you see a funny, distorted signal coming out at 115,200 baud, take a moment to clean its edges up and see what you’ve got.

Seeking Treachery in a Questionably Sourced Phone

Have you ever considered sourcing an off-brand phone from the China markets? Why, or what stopped you? The answer is data and identity. You are trusting both when you decide to use a smartphone. Let’s face it, smartphones are a personality prosthesis in our society. They know your physical location, what your interests are, the people you hang out with, and how you spend your money. The keys to the castle are shared with these devices and you shouldn’t grant that kind of trust without knowing your phone is worthy of it.

But… what if that phone has amazing features at an equally amazing price? [ijsf] bought the phone and then made it earn the proper level of trust. The model in question is a Blackview BV6000s — pictured above in a tub of soapy water proving it’s IP68 claim. This thing has flagship specs but not a flagship name so [ijsf] took [Dave Jones’] advice and took it apart instead of turning it on. In this case, it is a complete ROM dump and disassembly.

The goals was to find malware — anything that is potentially leaking data. Nothing was found, which we think is because this phone isn’t nearly shady enough. We’d expect the bargain basement models (like this $3 wonder vaporware) to be more in line. That one actually has a carrier behind it which means they plan to recoup on usage charges. But suspiciously cheap phones may be using a business model that makes it back by stealing a chunk of your identity.

Two good things come out of [ijsf’s] writeup. First, it’s a decent guide to dumping and snooping in a ROM. Second, in addition to the fruitless search for thieving apps, the annoying bloatware was removed for a cleaner ‘stock’ image.

Arduino Absentmindedly Blows Bubbles

If you ever wanted to make an occasion festive with bubbles, [Sandeep_UNO] may have the project for you. As you can see in the video below (and, yes, it should have the phone rotated and it doesn’t), his Arduino uses a servo motor to dip a bubble wand into soap solution and then pulls it in front of a fan. The entire operation repeats over and over again.

There’s not a lot of detail and no code that we could find, but honestly, if you know how to drive a servo motor from an Arduino, the rest is pretty easy to figure out. Look closely at the motion of the robot. What is often accomplished with a spinning wheel of bubble wands and a constant fan becomes much more interesting when applied intermittently. The lazy cadence is what you expect to see from human operation and that adds something to the effect.

We’ve seen faster bubble blowers, but they were not so simple. We’ve even looked at other bubble-blowing robots. If you want to find out more about servo motors in general, our own [Richard Bauguley] has what you need to know.

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Fight That Tesla Envy With A Tablet Dash For Your Car

[Aykut Çelik] uses some strong words to describe how he feels about his VW Polo’s current radio set-up. Words like, “useless,” are bandied about. What is a modern man supposed to do with a car that doesn’t have built-in navigation or Bluetooth connectivity with phones? Listen to the radio? There are actual (mostly) self driving cars on the road now. No, [Aykut] moves forward, not backwards.

To fix this horrendous shortcoming in his car’s feature package, he set out to install a tablet in the dash. His blog write-up undersells the amount of work that went into the project, but the video after the break rectifies this misunderstanding. He begins by covering the back of a face-down Samsung tablet with a large sheet of plastic film. Next he lays a sheet of fiberglass over the tablet and paints it with epoxy until it has satisfactorily clung to the back of the casing. Afterwards comes quite a bit of work fitting an off-the-shelf panel display mount to the non-standard hardware. He eventually takes it to a local shop which does the final fitting on the contraption.

The electronics are a hodgepodge of needed parts: An amplifier, to replace the one that was attached to the useless husk of the prior radio set; a CAN shield for an Arduino, so that he could still use the steering wheel buttons; and a Bluetooth shield, so that the Arduino could talk to the tablet. Quite a bit of hacking happened, and the resulting software is on GitHub.

The final assembly went together well. While it’s no Tesla console. It does get over the air updates whenever he feels like writing them. [Aykut] moves forward with the times.

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TV Stick Out-Raspberries Raspberry Pi

Android-based TV sticks should be in more projects. They are readily available and inexpensive. They have a lot of horsepower for the price, and they can even boot a mainline Linux kernel, unlike some single-board computers we know. They’re smaller than the Pi Zero, so they’ll fit almost anywhere.

The one thing they don’t have, though, is I/O. Sure, it’s got a USB port, but that’s just about it. [Necromant] considered these problems and created a carrier board that fixes all that.

  • On-board 3A DC-DC. You can power the whole thing with anything from 7 to 24 volts DC
  • A 4-Port USB hub
  • An ATtiny 2313, connected to the hub via the V-USB stack
  • 2 USB ports on the back, with power control via GPIO lines
  • One USB port on the front (with power always on)
  • 3 relays
  • Fits a common anodized aluminum enclosure

The ATtiny code is on GitHub and allows for full I/O control, saving the state of the pins in EEPROM, and providing up to eight channels of servo control. The device connects through the USB port (consuming one port on the hub).

Repurposing consumer gear for embedded service is nothing new. We’ve seen it with phones. We’ve even seen remotes used as a mouse. But this is such a nice template for adding cheap and easy computing power to your projects that we’re surprised we don’t see it more often. Why aren’t you hacking a TV stick into your projects?

Death, Taxes, and Laundry

There’s an old saying that the only two things that are certain are death and taxes. However, unless you live in a nudist colony, there’s probably also laundry. [Darpan Bajaj] and some friends were at a hackathon and decided to put their washing machine on the Internet.

Most of us here at Hackaday — and many Hackaday readers, judging by the comments — are a little suspicious about how much we really need everything attached to the Internet. However, a washing machine is probably not a bad idea: you use it often, you need to know when it is done, and you probably don’t want to just sit and watch it spin. Besides, the intended installation is in a hostel where there are multiple machines and many potential users.

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