Flex PCBs Make Force-Mapping Pressure Sensor for Amputee

What prosthetic limbs can do these days is nothing short of miraculous, and can change the life of an amputee in so many ways. But no matter what advanced sensors and actuators are added to the prosthetic, it has to interface with the wearer’s body, and that can lead to problems.

Measuring and mapping the pressure on the residual limb is the business of this flexible force-sensing matrix. The idea for a two-dimensional force map came from one of [chris.coulson]’s classmates, an amputee who developed a single-channel pressure sensor to help him solve a painful fitting problem. [chris.coulson] was reminded of a piezoresistive yoga mat build from [Marco Reps], which we featured a while back, and figured a scaled-down version might be just the thing to map pressure points across the prosthetic interface. Rather than the expensive and tediously-applied web of copper tape [Marco] used, [chris] chose flexible PCBs to sandwich the Velostat piezoresistive material. An interface board multiplexes the 16 elements of the sensor array to a PIC which gathers and records testing data. [chris] even built a test stand with a solenoid to apply pressure to the sensor and test its frequency response to determine what sorts of measurements are possible.

We think the project is a great application for flex PCBs, and a perfect entry into our Flexible PCB Contest. You should enter too. Even though [chris] has a prototype, you don’t need one to enter: just an idea would do. Do something up on Fritzing, make a full EAGLE schematic, or just jot a block diagram down on a napkin. We want to see your ideas, and if it’s good enough you can win a flex PCB to get you started. What are you waiting for?

There are 10 Kinds of Computers in the World

There’s an old joke that there are 10 kinds of people in the world. Those who know binary, those who don’t, and those who didn’t see a base three joke coming. Perhaps [Dmitry Sokolov] heard that joke because he’s built a ternary (base 3) computer. He claims it is the first one to be built in the last 50 years. You can see a video about the device below. There’s also a video of the device with a nixie tube output.

You may not think of it often, but bit is a contraction of binary digit, so a ternary computer doesn’t have those. It has trits. The CPU operates on 3 trit words and uses nothing but multiplexers as building blocks. Instructions use 5 trits, some of which are a two-trit opcode and a 3 trit address of one of the 13 registers. The allure of using ternary, by the way, is that you can represent more numbers in fewer bits — um, trits, rather.

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Why Only Use One Controller When You Can Use ALL Of Them?

After booting up his RetroPie system, [jfrmilner] had the distinct feeling that something was off. Realizing that the modern Xbox 360 controller didn’t fit right when reliving the games of his youth, he rounded up all his old controllers to make sure he always had the right gamepad for the game.

Wanting to keep the controllers unmodified — so they could still be used on the original systems — he had to do a bit of reverse-engineering and source some controller sockets before building his controller hub. Using shift-in registers, shift-out registers, and some multiplexers, he designed a large circuit selector — which acts as a shield for an Arduino Micro — so all the controllers remain connected. A potentiometer allows him to select the desired controller and a few arcade buttons which access RetroPie shortcuts really round out the hub. Check out the demo after the break!

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A Few of Our Favorite Chips: 4051 Analog Mux

Raindrops on roses, and whiskers on kittens? They’re alright, I suppose. But when it comes down to it, I’d probably rather have a bunch of 4051, 4052, and 4053 analog multiplexers on the component shelf. Why? Because the ability to switch analog signals around, routing them at will, under control of a microcontroller is tremendously powerful.

Whether you want to read a capacitive-sensing keyboard or just switch among audio signals, nothing beats a mux! Read on and see if you agree.

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Neopixels Light the Way in Pressure-Sensitive Floor

It’s got a little “Saturday Night Fever” vibe to it, but this pressure-sensitive LED floor was made for gaming, not for dancing.

Either way, [creed_bratton_]’s build looks pretty good. The floor is a 5×6 grid of thick HDPE cutting boards raised up on a 2×4 lumber frame. Each cell has a Neopixel ring and a single force-sensitive resistor to detect pressure on the pad. Two 16-channel multiplexers were needed to consolidate the inputs for the Arduino that’s running the show, and a whole bunch of wall warts power everything. The video below shows a little of the build and a look under the tiles. It’s not clear exactly what game this floor is for, but you can easily imagine a maze or some other puzzle that needs to be solved with footsteps.

Light-up floors are nothing new here, what with this swimming pool dance floor. But this interactive dance floor comes close to the gaming aspect of [creed_bratton_]’s build.

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Pneumatic Multiplexer

This is a pretty cool project [Sebastian Morales] is working on – a 3D printed Pneumatic Multiplexer. Large interactive installations, kinetic art and many other applications require large numbers of actuators to be controlled. For these type of projects to work, a large number of actuators equals higher resolution and that allows the viewer to be captivated by the piece.

The larger the system becomes, the more complex it becomes to control all of those actuators. [Sebestian] wanted to move a large number of components with a relatively low number of inputs. He thought of creating a mechanical equivalent of the familiar electronic X-Y matrix that can control large quantities of outputs using only a few inputs – in a more descriptive form, Outputs=(Inputs/2)^2.

airlogic_01He looked at chemical reactions that change liquids in to gases, but that seemed pretty complicated. Refrigerants used in air conditioning looked promising, but their handling and safety aspects looked challenging.

Eventually, he decided to look at using “air logic“. Air logic uses pneumatic devices to create relays, limit switches, AND gates, NAND gates, OR gates, amplifiers, equivalent to electrical circuits. Electrical energy is replaced with compressed air. His plan was to build a multiplexer whose elements would open only if the combination of pressure between both lines was the right one. As in electronics, NAND logic is easy to implement. A moving element creates a seal and only allows air out if the bottom line was low and the top line was high.

He had access to a high resolution, resin based 3D printer which allowed him to create fully air-tight systems. He started with prototyping a small 4×4 matrix to test out his design, and had to work through 6 to 7 iterations before he could get it to work. The next step was to create a larger matrix of 100 elements controlled by 20 inputs (10×10 matrix). He created Omnifarious – a kinetic sculpture demonstrating the concept of shapeshifting objects. The Omnifarious is a hexecontahedron which would be able to transform its surface to render different geometries via 59 balloons on its surface. Below, you can check the videos of his progress building the various prototypes and another video showing the Omnifarious sculpture.

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