Reverse Engineering a Bathroom Scale for Automated Weight Tracking

Bathroom Scale

[Darell] recently purchased a fancy new bathroom scale. Unlike an average bathroom scale, this one came with a wireless digital display. The user stands on the scale and the base unit transmits the weight measurement to the display using infrared signals. The idea is that you can place the display in front of your face instead of having to look down at your feet. [Darell] realized that his experience with infrared communication would likely enable him to hack this bathroom scale to automatically track his weight to a spreadsheet stored online.

[Darell] started by hooking up a 38khz infrared receiver unit to a logic analyzer. Then he recorded the one-way communication from the scale to the display. His experience told him that the scale was likely using pulse distance coding to encode the data. The scale would start each bit with a 500ms pulse. Then it would follow-up with either another 500ms pulse, or a 1000ms pulse. Each combination represented either a 1 or a 0. The problem was, [Darell] didn’t know which was which. He also wasn’t sure in which order the bits were being transmitted. He modified a software plugin for his logic analyzer to display 1’s and 0’s on top of the waveform. He then made several configurable options so he could try the various representations of the data.

Next it was time to generate some known data. He put increasing amounts of weight on the scale and recorded the resulting data along with the actual reading on the display. Then he tried various combinations of display settings until he got what appeared to be hexadecimal numbers increasing in size. Then by comparing values, he was able to determine what each of the five bytes represented. He was even able to reconstruct the checksum function used to generate the checksum byte.

Finally, [Darell] used a Raspberry Pi to hook the scale up to the cloud. He wrote a Python script to monitor an infrared receiver for the appropriate data. The script also verifies the checksum to ensure the data is not corrupted. [Darell] added a small LED light to indicate when the reading has been saved to the Google Docs spreadsheet, so he can be sure his weight is being recorded properly.

Toddler Jukebox Requires No Quarters or Button Mashing

songblocksAhh, toddlers. They’re as ham-fisted as they are curious. It’s difficult to have to say no when they want to touch and engage with the things that we love and want them to play with. [Shawn] feels this way about his son’s interest in the family Sonos system and engineered an elegant solution he calls Song Blocks.

The Sonos sits on a dresser that hides a RasPi B+. Using bare walnut blocks numbered 1-12, his son can use the Sonos without actually touching it. Each block has a magnet and an NFC tag. When his son sticks a block on the face of the right drawer containing embedded magnets and an NFC controller board, the B+ reads the tag and plays the song. It also tweets the song selection and artist.

The blocks themselves are quite beautiful. [Shawn] numbered them with what look like Courier New stamps and then burned the numbers in with a soldering iron. His Python script is on the git, and he has links to the libraries used on his build page. The Song Blocks demo video is waiting for you after the jump.

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120 Node Rasperry Pi Cluster for Website Testing

raspicluster1

[alexandros] works for resin.io, a website which plans to allow users to update firmware on embedded devices with a simple git push command. The first target devices will be Raspberry Pis running node.js applications. How does one perform alpha testing while standing up such a service? Apparently by building a monster tower of 120 Raspberry Pi computers with Adafruit 2.8″ PiTFT displays. We’ve seen some big Raspberry Pi clusters before, but this one may take the cake.

raspicluster2

The tower is made up of 5 hinged sections of plywood. Each section contains 24 Pis, two Ethernet switches and two USB hubs. The 5 sections can be run on separate networks, or as a single 120 node monster cluster. When the sections are closed in, they form a pentagon-shaped tower that reminds us of the classic Cray-1 supercomputer.

Rasberry Pi machines are low power, at least when compared to a desktop PC. A standard Raspi consumes less than 2 watts, though we’re sure the Adafruit screen adds to the consumption. Even with the screens, a single 750 watt ATX supply powers the entire system.

[alexandros] and the resin.io team still have a lot of testing to do, but they’re looking for ideas on what to do with their cluster once they’re done pushing firmware to it. Interested? Check out their Reddit thread!

Feed That Shoulder Boom Box with a Wrist Tune Transmitter

rasrad-arm

Next time you’re strutting down the block with that hi-fi on you shoulder, don’t subject yourself to the limitations of a radio station’s tight playlist or the short run time of a cassette tape. Pack your tunes on your wrist and beam them directly with this wearable FM transmitter. No wires… it’s like the future is now!

The Raspberry Pi has proven itself to be a dependable FM transmitter. This project follows in those footsteps but moves the goal line a few leaps further. The build has a full user interface which will make it easy to adapt to just about any application you can imagine. And the added twist is shown in the latter third of the video after the break. [Navic209] has included a microphone in the design which allows the wearer to transmit voice to an appropriately tuned radio. It gives the device a very Dick Tracey-esque feel.

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Supercapacitors for the Raspberry Pi

supercapacitor ups

As versatile as the Raspberry Pi is, it has a weakness when it needs to be able to shut down properly during a power outage, especially when handling data-sensitive or industrial applications. To solve this problem, [Pavol Sedlacek] has created a supercapacitor-based UPS specifically for the Raspberry Pi that gives it enough time to properly halt its processes and shut down if it detects a power failure.

The device is called the Juice4Halt. It uses a DC-DC converter to provide power to the Pi from the normal power supply and to charge the supercapacitors during normal operation. It is bidirectional, so in the event of a power failure it works in reverse to take power from the capacitors and feed it back to the Pi. A second DC-DC converter handles power from an external power supply.

A side effect of using supercapacitors as a UPS is that they can also help the Pi survive brownouts. The project site has an incredible amount of detail about the functionality of the device, including circuit diagrams and the source code. We’ve seen other supercapacitor-based UPS units before but this particular one is much more robust and would be truly at home in any industrial or other sensitive setting.

Camera Mod Lets this Raspberry Pi Shoot in Different Spectrums

Raspberry Pi IR camera

For [Peter Le Roux'] first “real” electronics project, he decided to make a camera based off the venerable Raspberry Pi platform. But he didn’t just want a regular camera, he wanted something that could shoot in near IR wave lengths…

It’s a well-known fact that you can remove the IR blocking filter from most cameras to create a quasi IR camera hack – heck, that hack has been around nearly as long as we have! The problem is even if you let the IR light into the camera’s sensor, you still get all the other light unless you have some kind of filter. There are different ways of doing this, so [Peter] decided to do them all with an adjustable wheel to flip through all the different filters.

He designed the case after the PiBow enclosure – you can see our full Pi Case Roundup here – and had it all laser cut out of wood. Stick around after the break to see a nice explanation of the light spectrum and the various filters [Peter] uses.

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Sweet Stepper of [Jeremy]‘s Rocks Out with its Box Out

Stepper motor MIDI music boxInspired by the floppy drive orchestras of others, [Jeremy] has built a Pi-driven MIDI music box with stepper motor resonators and outlined the build on hackaday.io.

Control for the motors comes from an Iteaduino Mega 2560. The music starts as a MIDI file, gets processed into a text file, and is played over serial by a Raspberry Pi. He’s added percussion using K’NEX instruments and 9g servos, which we think is a nice touch. It can be powered via LiPo or from the wall, and [Jeremy] baked in protection against blowing up the battery. As he explains in the tour video after the break, the box is clamped to a wooden table to provide richer sound.

[Jeremy]‘s favorite part of the build was enclosing the thing as it was his first time using panel-mount components. Stick around to see a walk-through of the guts and a second video demonstrating its musical prowess.

[Read more...]

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