Reverse Engineering A Bathroom Scale For Automated Weight Tracking

October 18, 2014 by Rick Osgood 16 Comments

[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.

Small-Scale Projects Use Snail-Mail Mail-Scale

April 26, 2014 by Rich Bremer 12 Comments

stamps.com scale

Stamps.com offers a free USB scale when you sign up for their service. The first versions of this scale did not have a display. In order to find the weight of an object the scale had to be connected to a computer running the stamps.com software. If you happen to have one of these old scales or are able to pick one up cheap, you may be interested in using it outside of the stamps.com service. There are several options on how to do that.

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Hacking Digital Scales For The Disabled

December 18, 2013 by Marsh 4 Comments

analphabeticscale

[Jan] works with both physically and mentally disabled individuals, some of whom cannot read, making many of their tasks more difficult. Although [Jan] is not in a position to teach reading or writing skills, he was able to build an add-on device for the scales used in repackaging sweets to provide simple feedback that the user can interpret.

The device has three LEDs—red, green, and yellow—to indicate the package does not weigh enough (red), weighs too much (yellow), or lies within an acceptable range (green). The industrial scales at [Jan’s] workplace each have a serial output to connect to a printer, which he used to send data to the device. An ATMega8 controls the lights and an attached LCD, with the usual trimpot to change the display’s contrast and a rotary encoder to adjust the device’s settings. Everything fits snugly into a custom-made frosted acrylic enclosure, laser-cut at a local hackerspace.

[Jan] provides a rigorous guide to approaching each step on his Instructables page, along with source code and several pictures. See a video overview below, then enjoy another scale hack: building one from scratch.

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Posterior Posture Videogame Controller

November 19, 2013 by Todd Harrison 6 Comments

Normally we see some crazy mad science projects coming from [Ben Krasnow’s] laboratory. This week [Ben] changes gears a bit and hacks his Xbox controller to interface with his bathroom scale and function as a posture controlled input device. You may want to take a moment for that to tumble around in your noggin before we trying to explain. What this means is you sit catawampus on a bathroom scale and when you lean forward your game character moves forward, lean back your character backs up and lean side to side for strafe left and right.

A modern digital bathroom scale has four pressure point transducers — one in each corner — which are read by the central controller and summed to generate the weight of the object setting on the scale. To use the scale as a controller input [Ben] removed the central scale controller and created two amplified Wheatstone bridge differential circuits, one for each diagonal axis between load cells. After adding an offset potentiometer to fix the resting point at 0.8 volts, the amplified differential voltage signals are fed directly into an Xbox controller’s thumb stick input for game control.

Additionally, to add rotation to his new game controller he hacked a an old ball type mouse and added a bit of rubber tubing that contacted and tracked the base of a Lazy Susan platter. The scale sits on the Lazy Susan and allows for the partial rotation of your torso to controlled game rotation. However, [Ben] still needed a regular mouse interfaced with the game for full 360° rotation control.

There is more after the break, plus the build and demonstration video.

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Hackaday Links: September 15, 2013

September 15, 2013 by Mike Szczys 10 Comments

First a quick announcement. We changed our “Kickstarter” category to “Crowd Funding“. We get a huge number of tips about crowd funding projects. We’re always interested in details. If you’re trying to get your crowd funding campaign on our front page make sure you’ve shared as many gritty project details (development process, problems/successes along the way, etc.) as possible . We usually prefer if this is done in a separate blog post from the campaign page itself.

Here’s a peephole hack that purportedly cost four grand. It uses a full on DSLR for the peephole hardware. Add a motion sensor and maybe you’ll be able to learn the faces of the neighbors who live on your floor. [via Gizmodo]

[Matthias] tells us that support for Rigol DS1052E oscilloscopes has been included in the 3.11 version of the Linux Kernel. Prior to this, getting the hardware to work on Linux was a hack, and a buggy one at that. For what it’s worth, here’s confirmation that support was added.

A post about reverse engineering the FitBit Aria Wi-Fi scale was sent in by [Christopher]. This makes us wonder if you could patch into a digital scale, using your own electronics to spoof the FitBit version?

We always keep our paperboard six-pack carriers so that we have a way to transport our homebrew beer. But rolling into a party with this laser-cut beer caddy which [Daniel] designed looks a lot cooler.

Texas Instruments has an MSP430 Selection Guide (PDF) which we found interesting. The first nine pages or so are pretty much just marketing, but several pages of parametric tables found after that make for a great collection of data on the hardware families. [via Dangerous Prototypes]

[Antoine] spared no expense building a coffee table that showcases his old motherboards. The illuminated glass and wood art piece rang in at around $400 in materials. We’re a little more minimalist with our home decor. We still want something along the lines of this LED matrix version.

Speaking of LED matrices, [Mario] dropped off a link to his LED Space Invaders game in the comments of last week’s Game of Light post. What we can’t figure out is why so many people hesitate to send in a tip about their awesome projects?

Adding A Display To A USB Digital Scale

September 13, 2013 by Phillip Ryals 16 Comments

[Oleg] found himself in possession of a Stamps.com Model 510 5lb digital scale. It’s a great scale, but only works as a USB HID device. In other words, it’s a digital scale without a digital display. He decided he wanted it to be more standalone, so he added a Toshiba HD44780 (compatible) display. An Arduino UNO and USB Host shield were used to make it happen. His sketch simply polls the scale and outputs the weight on the display.

In this case, he used the USB Host Shield from Circuits at Home, but a brief look shows they use the same MAX3421 controller chip as Sparkfun and other versions of the board. You might also be able to pull off the same functionality with an AVR running V-USB, though admittedly it wouldn’t be so easy.

We haven’t found a great way to add USB host mode to projects other than shields like the one [Oleg] used. If you know of a better way, share your ideas in the comments.

Of course, if this isn’t hardcore enough for you, forget using a consumer scale – make your own from scratch!

Building A Digital Scale From Scratch

June 12, 2013 by Brian Benchoff 13 Comments

duplo

[Raivis] was given a particular task at his university – find a way to measure how many Duplo bricks are stacked together. There are a number of ways to do this, everything from computer vision to using a ruler, but [Raivis] chose a much more educational method. He built a digital scale from scratch out of a strain gauge and a Wheatstone bridge. The build log is immensely educational and provides some insight into the challenges of weighing things digitally.

A strain gauge is a simple piece of equipment, just a small force sensitive resistor. When attached to a metal bar and a force is applied, the resistance inside the strain gauge changes, but not by much. There’s only a few micro Ohms difference between the minimum and maximum of [Raivis]’ load cell, so he needed a way to measure very slight changes in resistance.

The solution was a Wheatstone bridge, or four resistors arranged in a square. When one of the resistors in the bridge is replaced with a strain gauge, very small changes in resistance can be measured.

With a custom ‘duino amplifier shield, [Raivis] can measure the resistance of his load cell with 10-bit resolution, or a maximum weight of 1.32 kg with a resolution of two and a half grams. A single duplo block weighs about 12 grams, so we’ll call this one a success.