A Tutorial On Using Linux For Real-Time Tasks

April 25, 2014 by Adam Fabio 15 Comments

[Andreas] has created this tutorial on real-time (RT) tasks in Linux. At first blush that sounds like a rather dry topic, but [Andreas] makes things interesting by giving us some real-world demos using a Raspberry Pi and a stepper motor. Driving a stepper motor requires relatively accurate timing. Attempting to use a desktop operating system for a task like this is generally ill-advised. Accurate timing is best left to a separate microcontroller. This is why we often see the Raspi paired with an Arduino here on Hackaday. The rationale behind this is not often explained.

[Andreas] connects a common low-cost 28BYJ-48 geared stepper motor with a ULN2003 driver board to a Raspberry Pi’s GPIO pins. These motors originally saw use moving the louvers of air conditioners. In general, they get the job done, but aren’t exactly high quality. [Andreas] uses a simple program to pulse the pins in the correct order to spin the motor. Using an oscilloscope, a split screen display, and a camera on the stepper motor, [Andreas] walks us through several common timing hazards, and how to avoid them.

The most telling hazard is shown last. While running his stepper program, [Andreas] runs a second program which allocates lots of memory. Eventually, Linux swaps out the stepper program’s memory, causing the stepper motor to stop spinning for a couple of seconds. All is not lost though, as the swapping can be prevented with an mlockall() call.

The take away from this is that Linux is not a hard real-time operating system. With a few tricks and extensions, it can do some soft real-time tasks. The best solution is to either use an operating system designed for real-time operation, or offload real-time operations to a separate controller.

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Black Mirror, Black Hole: Kill Your Television

April 23, 2014 by Kristina Panos 15 Comments

don't waste your time TV screen Would you believe that some people think the internet is a time waster? Well, not at this particular address of course, but we can think of some other sites that are absolute rabbit holes without so much as a rousing game of croquet at the bottom. If you need help achieving what Tim Ferriss dubbed a Low Information Diet, there are browser extensions that will block your access to sites that keep you from getting things done. [Ivan’s girlfriend] has taken this time management tack seriously and even created a simple web page that states “Don’t Waste Your Time!” that will show if she tries to get to Facebook.

There’s one small problem with all this, and it’s been around for a long time. [Ivan’s girlfriend] still watches TV. Out of love and respect for her goals, he decided to prank her by blocking her TV viewing. In a delightful twist, the TV will display her own web page to her after 30 seconds.

They have digital and analog TVs, so he had to set up both in order to cover his bases. The digital TV is a monitor fed from a set-top box with HDMI out. As the STB can only be controlled via IR remote, [Ivan] used an HDMI switch to change from the STB input to a Raspi that will display the reprimanding web page and play Pink Floyd’s “Time“.

The analog TV took slightly more doing. He put a Raspi on the AV input, but connected it from the inside so nothing looked suspicious. The Raspi checks the TV status every second and switches to the Pi once the TV is on. Same deal: judgmental web page, Pink Floyd. The beauty part is that both of [Ivan]’s setups also record her reaction; the digital TV uses a dash camera and the analog uses an Android phone. Check out [Ivan]’s tour of the analog TV Pi after the break.

If you or [Ivan’s girlfriend] need even more time management help, there’s always the roll-your-own-Pomodoro timer.

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HummingBoard, The Vastly More Powerful Raspi

April 22, 2014 by Brian Benchoff 76 Comments

The Raspberry Pi has been around for a while now, and while many boards that hope to take the Pi’s place at the top of the single board ARM Linux food chain, not one has yet succeeded. Finally, there may be a true contender to the throne. It’s called the HummingBoard, and packs a surprising amount of power and connectivity into the same size and shape as the venerable Raspberry Pi.

The HummingBoard uses a Freescale i.MX6 quad core processor running at 1GHz with a Vivante GC2000 GPU. There’s 2GB of RAM, microSD card slot, mSATA connector, Gigabit Ethernet, a BCM4329 WiFi and Bluetooth module, a real-time clock, and IR receiver. There’s also all the usual Raspberry Pi flair, with a 26 pin GPIO connector, CSI camera connector, DSI LCD connector, stereo out, as well as the usual HDMI and analog video.

The company behind the HummingBoard, SolidRun, hasn’t put a retail price on the board, nor have they set a launch date. You can, however, enter a contest to win a HummingBoard with the deadline this Friday. Winners will be announced in early May, so maybe the HummingBoard will be officially launched sometime around then.

It’s an amazing board with more than enough power to rival the extremely powerful BeagleBone Black, with the added bonus of being compatible with so many of those Raspberry Pi accessories we all love dearly.

Sniping 2.4GHz

April 21, 2014 by Brian Benchoff 42 Comments

A long time ago when WiFi and Bluetooth were new and ‘wardriving’ was still a word, a few guys put a big antenna on a rifle and brought it to DefCon. Times have changed, technology has improved, and now [Hunter] has built his own improved version.

The original sniper Yagi was a simple device with a 2.4 GHz directional antenna taped onto the barrel, but without any real computational power. Now that displays, ARM boards, and the software to put this project all together are cheap and readily available, [Hunter] looked towards ubiquitous computing platforms to make his Sniper Yagi a little more useful.

This version uses a high gain (25dBi) antenna, a slick fold-out screen, and a Raspberry Pi loaded up with Raspberry Pwn, the pentesting Raspi distro, to run the gun. There’s a button connected to the trigger that will automatically search the WiFi spectrum for the best candidate for cracking and… get cracking.

[Hunter] says he hasn’t taken this highly modified airsoft rifle outside, nor has he pointed out a window. This leaves us with the question of how he’s actually testing it, but at least it looks really, really cool.

Raspberry Pi Remote Audio Link

April 17, 2014 by Eric Evenchick 7 Comments

In broadcast, lots of people are still using dedicated analog lines to connect remote sites. These operate like old telephone systems: you call up the operator and request to be patched through to a specific site. They’re also rather expensive.

For a hospital radio station, [Marc] wanted to replace the old system with something less costly. The result is his Raspberry Pi STL in a Box. Inside the box is a Raspberry Pi, PiFace display, a pair of meters, and some analog hardware for the audio.

On the software side, the system uses LiquidSoap to manage the stream. LiquidSoap uses a language to configure streams, and [Marc] has a write-up on how to configure LiquidSoap for this application. On the hardware side, SSM2142 ICs convert the signal from single-ended to balanced. The meters use the LM3915 bar drivers to control the meters.

The Python script that controls the box is provided, and could be helpful for anyone needing to build their own low-cost audio link.

Neo Geo Arcade Gets Second Life With A Raspberry Pi

April 14, 2014 by Adam Fabio 9 Comments

neo-picade

An old Neo Geo Arcade, a Raspberry Pi, and some time were all [Matthew] needed to build this Pi Powered Arcade Emulator Cabinet.

Neo Geo was originally marketed by SNK as a very expensive home video console system. Much like the Nintendo Play Choice 10, SNK also marketed an arcade system, the MVS. The Neo Geo MVS allowed arcade operators to run up to six titles in a single cabinet. The MVS also allowed players to save games on memory cards.

[Matthew’s] cabinet had seen better days. Most of the electronics were gone, the CRT monitor was dead, and the power supply was blown. Aside from a bit of wear, the cabinet frame was solid and the controls were in good shape. He decided it would be a good candidate for an emulator conversion.

We’ve seen some pretty awesome arcade conversions in the past, such as this Halloween rendition of Splatterhouse. For his conversion, [Matthew] stuck to the electronics, leaving most of the old arcade patina intact. The CRT did fire up after some components were replaced. [Matthew] ran into some refresh rate issues with the Raspberry Pi, so he opted to swap it out with a modern LCD monitor. Controls were wired up with the help of an I-PAC board.

[Matthew] had to write a driver to handle the I-PAC, but he says it was a good learning experience. Aside from the LCD screen, the result looks like it could be found in the back of an old bowling alley, or a smokey bar next to Golden Tee. Nice work, [Matthew]!

Hackaday Links: April 13, 2014

April 13, 2014 by Mike Szczys 13 Comments

Check out this Pokemon Yellow cartridge for Super Nintendo. Wait, what? That is a Game Boy game! Well there is a Super Gameboy cartridge that lets you play them on SNES. This mashes the guts of the two into a custom-decorated SNES cart. Now if you’re more interested in the guts of that Super Game Boy cartridge you’ll want to check out this classic hack which dumped the ROM from it. [Thanks Nick]

Here are a couple of interesting things from our friends over at Adafruit. First off, they have a high-res gallery of the Raspberry Pi compute module and carrier boards which we heard about earlier in the week. Also, the latest Collin’s Lab has a great video on soldering. We especially appreciated the discussion of soldering iron tips and their effect on heat transfer.

[Marius] got tired of the static shock from the office coat rack. You know, like the scene straight out of Office Space? But he didn’t disassemble the infrastructure to solve the issue. Instead he connected it directly to ground. Just make sure you stick the wire in the correct hole!

It’s as if Hackaday is on a quest for the most perfect DIY cyclonic separator. Here’s the latest offering which you can cut out from sheet stock by hand. It’s the alternative for those of us without access to a 3D printer.

If you think it’s too difficult to build what we refer to as a Daft Punk table you need to check out what [Dan] pulled off. He proves that your LED matrix coffee table project doesn’t have to take up a ton of time or cost an exorbitant amount of cash.

We should have mentioned this to you before the weekend so you’d have something to watch: you can now download BBS: The Documentary from the Internet Archive. We’ve watched the entire thing and it’s fantastic. If you know what a dial-up modem handshake sounds like, you’re going to be awash in nostalgia. If you don’t know the delight of those sounds you need to watch this and see how things used to be back in the day when connecting your computer to a network definitely wasn’t what the cool kids were doing. [Thanks Larry]