The Bad Old Days Of Telephone Answering Machines

July 12, 2018 by 55 Comments

Telephone answering machines were almost a fad. They were hindered for years by not being allowed to connect to the phone lines. Then a mix of cell phones and the phone company offering voicemail made the machines all but obsolete. Unless you are really young, you probably had one at some point though. Some had digital outgoing messages and a tape to record. Some had two tapes. But did you ever have one that didn’t connect to the phone line at all? Remember, there was a time when they couldn’t. My family had one of these growing up and after doing enough research to find it in an old catalog, I decided you might like to know how it really worked.

Even if you grew up in the 1960s and 1970s, it is hard to imagine how little technology there was in an average person’s home at that time. You probably had one TV and one wired telephone. You probably had a radio or two and maybe even a record or tape player. If you were very fancy, you had a big piece of furniture that had a TV, a turntable, a radio, and a tape player in it. No cell phones, no computers, no digital assistant, and appliances were electro-mechanical and didn’t have displays. So when you saw a new piece of tech — especially if you were a kid who didn’t know what a hacker was, but still wanted to be one — it made an impression.

I still remember the first time I even saw a tape recorder. I was amazed! But a tape recorder is a far cry from a telephone answering machine.

A Bit of Background

My Dad always had a regular job and his side business. He had a lot of different side businesses at one time or another, but he was always concerned about missing a phone call from a customer. We had two phones: the old wall mount phone with a dial and another desk phone in the “store” (the front room of the house) which also had a dial — we were way too cheap to pay for TouchTone service.

Remember, there was no call waiting and getting a second phone line was out of the question for my frugal parents. So they were always nervous about keeping the phone line clear during the day. But if you had to leave, you might miss a call. What do you do about that?

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Dual Sensor Echo Locator Gives High Accuracy At Low Cost

July 12, 2018 by 19 Comments

Infrared certainly has its uses, but if you’re trying to locate objects, ultrasonic detection is far superior. It’s contact-less, undetectable to the human ear, and it isn’t affected by smoke, dust, ambient light, or Silly String.

If you have one ultrasonic sensor and a microcontroller, you can detect plenty of useful things, like the water level in a rain barrel or the distance traveled by a tablet along a rail. If you have two sensors and a microcontroller, you can pinpoint any object within a defined range using trigonometry.

[lingib]’s dual sensor echo locator uses two HY-SRF05s, but the cheap and plentiful HC-SR04s will work, too. Both sensors are arranged for maximum beam overlap and wired up to an Arduino Uno. One sensor’s emitter is blocked with masking tape, so all it does is listen.

When the system registers the object, it shows up as a red dot on a grid inside a Processing sketch along with a bunch of details like the object’s coordinates, its distance from each sensor, and the area of the triangle formed by the two sensors and the object. [lingib] reports that the system is quite accurate and will work for much larger playgrounds than the 1 meter square in the demo after the break.

Don’t want to detect objects? Ultrasonic sensors are cheap enough to hack into other things, like this one-way data communications module.

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It’s All In The Libs – Building A Plugin System Using Dynamic Loading

July 12, 2018 by 17 Comments

Shared libraries are our best friends to extend the functionality of C programs without reinventing the wheel. They offer a collection of exported functions, variables, and other symbols that we can use inside our own program as if the content of the shared library was a direct part of our code. The usual way to use such libraries is to simply link against them at compile time, and let the linker resolve all external symbols and make sure everything is in place when creating our executable file. Whenever we then run our executable, the loader, a part of the operating system, will try to resolve again all the symbols, and load every required library into memory, along with our executable itself.

But what if we didn’t want to add libraries at compile time, but instead load them ourselves as needed during runtime? Instead of a predefined dependency on a library, we could make its presence optional and adjust our program’s functionality accordingly. Well, we can do just that with the concept of dynamic loading. In this article, we will look into dynamic loading, how to use it, and what to do with it — including building our own plugin system. But first, we will have a closer look at shared libraries and create one ourselves.

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You Can Now Buy A Practical Gauss Gun

July 12, 2018 by 64 Comments

Occasionally we come across a piece of information which reminds us that, while flying cars are still nowhere to be found, we’re definitely living in the future. Usually it’s about some new application of artificial intelligence, or maybe another success in the rapidly developing field of private spaceflight. But sometimes it’s when you look at a website and say to yourself: “Oh cool, they have 1.5kW electromagnetic accelerators in stock.”

Arcflash Labs, a partnership between [David Wirth] and [Jason Murray], have put their EMG-01A Gauss gun up for sale for anyone who’s brave enough and willing to put down $1,000 USD on what’s essentially a high-tech BB gun. The creators claim it obtains an efficiency of 6.5% out of its RC-style 6S LiPo battery pack, which allows it to fire over 100 rounds before needing to be recharged. Firing 4.6g steel projectiles at a rather leisurely 45 m/s, this futuristic weapon would be more of a match for tin cans than invading alien forces, but at least you’ll be blasting those cans from a position of supreme technical superiority.

The EMG-01A builds on the work of the team’s previous experiments, such as the semi-automatic railgun we covered last year. They’ve made the device much smaller and lighter than their previous guns, as well as worked on making them safer and more reliable. That said, the page for the EMG-01A has a number of warnings and caveats that you won’t see on the back of a Red Ryder BB gun box; it’s certainly not a toy, and anyone who takes ownership of one needs to be respectful of the responsibility they’re taking on.

Speaking of which, who can actually buy one of these things? The Arcflash Labs site makes it clear they will only ship to the United States, and further gives a list of states and cities were they can’t send a completed gun. Essentially they are following the same laws and guidelines used for shipping air guns within the US, as they believe that’s a fair classification for their electromagnetic guns. Whether or not the ATF feels the same way is unclear, and it should be interesting to see what kind of legal response there may be if Arcflash Labs starts moving enough units.

If you’d like to wage warfare on your recyclables without spending quite so much cash, you can always build your own for less. Or nearly nothing, if you want to go the full MacGyver route.

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Old Laptop? Mobile X86 Game System!

July 12, 2018 by 5 Comments

Between smartphones and tablets, computing is becoming increasingly mobile in nature. It used to be that everyone had a desktop computer, then laptops became the norm, and now many people don’t have anything beyond their mobile device. Unless you’re the kind of person who actually needs the power and versatility offered by a “real” computer, mobile devices are simply a more convenient option to browse the web and consume content.

But what if your needs are somewhere in the middle? You want an x86 computer and full operating system, but you also want something that’s more mobile than a tablet? If you’re like [mnt], you take an old Atom laptop that’s on its last legs and rebuild it as the Hacktop.

[mnt] describes the Hacktop as an “Emergency Gaming/Hacking Station”, and says he uses it everywhere he goes. Inspired by his Nintendo DSi, gaming controls are front-and-center on the Hacktop and he uses the machine to play everything from Half-Life to classic emulators.

But the Hacktop is capable of more than just playing Amiga games. The hand-soldered QWERTZ keyboard can be used with his thumbs, and the D-Pad doubles as the cursor keys. There’s a laptop touch pad on the back of the case, and the ten-inch LCD display is a touch screen as well. Definitely no shortage of input devices on this thing. It’s also packing some interesting special features, such as integrated RTL-SDR and LIRC hardware for mobile exploration and experimentation. [mnt] says the nine-cell battery should keep it alive and kicking for twelve hours or so, but it of course depends on what kind of stuff he gets into while out and about.

Hackers have been building their own mobile devices for a long time, and we’re always struck by the creative approaches individuals take compared to the rather cookie-cutter world of mobile consumer technology.

Shoehorning A Slick Spotify Remote Into An ESP8266

July 11, 2018 by 9 Comments

In 2017 Spotify finally deprecated their public vanilla C SDK library,  libspotify, and officially replaced it with dedicated SDKs for iOS and Android and this new-fangled web thing we’ve all heard so much about. This is probably great for their maintainability but makes writing a native application for a Linux or a hardware device significantly harder, at least without an application process and NDA. Or is it? Instead of using that boring slab of glass and metal in their pocket [Dani] wanted to build a handy “now playing” display and remote control interface but was constrained by the aforementioned SDK limitations. So they came up with a series of clever optimizations resulting in the clearly-named ESP8266 Spotify Remote Control.

The Spotify Remote Control has a color LCD with a touchscreen. Once attached to a Spotify account it will show the album art of the currently playing track (with a loading indicator!) and let you play/pause/skip tracks from its touch screen, all with impressively low latency. To get here [Dani] faced two major challenges: authorizing the ESP to interact with a user’s Spotify account, and low latency LCD drawing.

2 Bit Cover Art

If you’re not on iOS or Android, the Spotify web API is the remaining non-NDA’d interface available. But it’s really designed to be used on relatively rich platforms such as fully featured web browsers, not an embedded device. To that end, gone are the days of asking a user to enter their username and password in a static login box, the newer (better) way is to negotiate for a per-user token (which is individually authorized per application), then to use that to authenticate your interaction. With this regime 3rd party applications (in this case an ESP8266) never see a user’s password. One codified and very common version of this process is called OAuth and the token dance is called a “workflow”. [Dani] has a pretty good writeup of the process in their post if you want more detail about the theory. After banging out the web requests and exception handling (user declines to authorize the device, etc) the final magic ended up being using mDNS to get the user’s browser to redirect itself to the ESP’s local web server without looking up an IP first. So the setup process is this: the ESP boots and displays a URL to go to, the user navigates there on a WiFi connected device and operates the authorization workflow, then tokens are exchanged and the Remote Control is authorized.

The second problem was smooth drawing. By the ESP’s standards the album art for a given track at full color depth is pretty storage-large, meaning slow transfers to the display and large memory requirements. [Dani] used a few tricks here. The first was to try 2 bit color depth which turned out atrociously (see image above). Eventually the solution became to decompress and draw the album art directly to the screen (instead of a frame buffer) only when the track changed, then redraw the transport controls quickly with 2 bit color. The final problem was that network transfers were also slow, requiring manual timesharing between the download code and the display drawing routing to ensure everything was redrawn frequently.

Check out [Dani]’s video after the break, and take a peek at the sources to try building a Spotify Remote Control yourself.

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Diode Recovery Time Explained

July 11, 2018 by 19 Comments

There are at least two phases to learning about electronics. In the first phase, you learn about how components are supposed to work. In the second phase, you learn about how they really work. Wires have resistance and inductance. Adjacent wires have capacitance. Capacitors leak. Inductors have resistance. All of these things matter. [Learnelectronics] has a recent video that explores recovery time for a diode — a phase two conversation.

If you haven’t run into recovery time before, it is the amount of time the diode takes to shut off after it is conducting. This manifests itself as a little undershoot where the signal that the diode should block leaks through briefly.

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