Electric Imp makes a cat door Tweet its activities


This Tweeting cat door uses the Electric Imp to read a sensor and report back to the server. The hardware is pretty neat. The board hosts an ARM Cortex-M3 processor and gets on your home network via WiFi. The mini-USB cable simply provides the power. Programming is done over the network. Our own [Brian Benchoff] had a chance to try the Imp out earlier in the Fall.

Monitoring a cat door is as good a reason as any to undertake a project. The hardware added to the board includes a reed switch mounted on the jamb along with a magnet on the door itself. There is also a blue LED that gives a bit of user feedback. The software isn’t quite as easy but it still wasn’t that bad. As with most web-connected projects getting all the parts to talk to each other was a bit of a chore. The Imp reports back to a server on the local network which then activates a PHP script that uses Sen.se to push out a Tweet.

[Thanks Pat]

Is entropy slowing down your Android device?


[Lambgx02] got tired of his Android device getting bogged down and decided to dig down to the cause of the issue. His investigation led him to believe that entropy is causing the slowdown. He believes that his workaround reduces 90% of the lag on the average Android device.

So how is it possible that entropy is causing the problem? It seems there is a bottleneck when an app requests a random number from the Linux kernel running at the lowest level of the device. Android is set up to use /dev/random for all random number requests, but [Lambgx02] says that location has a very shallow pool of numbers available. When they run out the kernel has to reload with a new seed and this is blocking the app that requested the data from continuing.

His solution was to write his own app that seeds /dev/random once every second using a number from /dev/urandom. He mentions that this might cause a security vulnerability as seeding the random data in this way is not quite as random. There may also be issues with battery life, so make sure to monitor performance if you give it a try.

[via Reddit]

Estimate velocity using quadrature encoder data

quadrature-encoder-velocityMany motors offer a quadrature encoder that give feedback on whether, and in which direction, the motor shaft is moving. But if you’re clever about analyzing the data you can use a quadrature encoder to estimate motor velocity. [Jason Sachs] makes the case that it’s fairly easy to get this wrong. Lucky for us he has carefully laid out his process of extrapolating velocity from the two edge-trigger data sources.

The process starts with reading from the encoder. Many chips have peripherals that will interface with a rotary encoder, but hardware lacking that built-in helper can still be used by monitoring pin-change interrupts. Once connected samples are taken over time and the rest is left to the quality of your algorithm.

What can this velocity data be used for? That’s up to you. But we can think of a couple of projects. It may be useful in a spinning POV display like this FPGA-based beauty. You also find quadrature encoders in exercise equipment. Knowing the velocity will help if you’re building your own computer to replace what came with that Stairmaster.

[via Reddit]

Dedicated Pandora player plus AirPlay built around the Raspberry Pi


[Shaun Gehring] wanted an Internet radio player. Although he did have some troubles along the way, the final project turned out very well. Housed inside this case which used to house a spindle of bland CDs is a Raspberry Pi that plays Pandora radio and serves as an AirPlay receiver.

The GPIO header of the RPi makes this project a lot easier. [Shaun] used Adafruit’s breakout board to solder connections for the six buttons and the character LCD screen. Plug some speakers into the audio jack and the hardware end of the deal is finished. The software side of things is very similar to the BeagleBone Pandora player we looked at in September. It uses a Linux distribution (Rasbian Weezy) and the Pianobar package.

Pianobar is very versatile. You can control it using a First-In First-Out file. Once [Shaun] figured out how to use mkfifo to set up the file, he was able to control it from a script by monitor button presses and echoing the associated command to the FIFO. The finishing touch was to add AirPlay support via the shairport package.

Van de Graaff generator built for a few dollars


This Van de Graaf generator was built using mostly parts on hand. The only thing that was purchased for the project was the Christmas ornament shaped M&M candy tin that serves as the collecting sphere. We didn’t include the in-action shot in the banner because it’s so dark. But sure enough, this will generate the visible sparks that make the device famous.

The gist of the device is that it uses rotating belt to generate static electricity. This potential is stored in the metal collecting sphere on top until a path for discharge is provided. They’re an awful lot of fun in middle-school science class as long hair can be made to stand on end if you touch one while your body is insulated from ground. This build uses a long rubber band as the belt. The band is moved by the motor from a DVD drive tray which is housed in the PVC base. An empty prescription pill bottle bridges the gap between the base and the metal sphere.

If this one is too small for you consider moving to a 900,000 Volt version.

[via Hacked Gadgets]

Case feeder makes your ammo reloading more efficient


For those that are into reloading their own ammo you know that getting an efficient assembly line process figured out will make your sessions much more enjoyable and productive. [Msoejacobsk] knew that he could buy a case feeder for his system, but didn’t want to shell out two hundred bucks for it. After a bit of thought he was able to build this case feeder for around ten dollars.

The purpose of the rig is to orient each empty casing correctly and feed it to the reloading hardware. This is accomplished by first separating one casing at a time using this angled tumbler. The disc that makes up the floor has slots cut in it which are the size of one casing. When that slot gets to the highest point of its rotation there is an opening through which the casing falls. To ensure proper orientation a V-shaped piece of heavy wire has been place in the middle of the opening. This acts as a fulcrum, letting the heavier base pull the casing in that direction. You can see this happen in the clip after the break.

[Read more...]

Pictures from weather satellites with a USB TV tuner


Several times a day, a NOAA weather satellite passes over your head, beaming down pictures of weather systems and cloud formations. These transmissions aren’t encrypted, and given the requisite hardware it’s possible for you to download these images from space as [Lovro] shows us in a tutorial video.

To get these near real-time satellite pictures, [Lovro] used one of those USB TV tuners we’ve grown so fond of. A somewhat specialized antenna is required to receive the right hand polarized transmissions from NOAA weather satellites, but with a few bits of wood and wire, [Lovro] made a helical antenna to listen in on the weather satellites transmitting around 137 MHz. After gathering a whole bunch of data from the satellites with SDRsharp, [Lovro] used an image decoder to turn an audio file into a picture taken from space just hours ago.

This isn’t the first time we’ve seen images from a NOAA weather satellite downloaded with a software defined radio; last year [hpux735] did just that with a somewhat inexpensive Softrock SDR. [Lovro]‘s use of a USB TV tuner to receive the transmission from NOAA satellites is a lot easier on the pocketbook, though, with the largest expense being an investment in time to build a helical antenna.