Hacking Touch Screens to Count Pulses

Heart rate sensors available for DIY use employ photoplethysmography which illuminates the skin and measures changes in light absorption. These sensors are cheap, however, the circuitry required to interface them to other devices is not. [Petteri Hyvärinen] is successfully investigating the use of capacitive touchscreens for heart rate sensing among other applications.

The capacitive sensor layer on modern-day devices has a grid of elements to detect touch. Typically there is an interfacing IC that translates the detected touches into filtered digital numbers that can be used by higher level applications. [optisimon] first figured out a way to obtain the raw data from a touch screen. [Petteri Hyvärinen] takes the next step by using a Python script to detect time variations in the data obtained. The refresh rate of the FT5x06 interface is adequate and the data is sent via an Arduino in 35-second chunks to the PC over a UART. The variations in the signal are very small, however, by averaging and then using the autocorrelation function, the signal was positively identified as a pulse.

A number of applications could benefit from this technique if the result can be replicated on other devices. Older devices could possibly be recycled to become low-cost medical equipment at a fraction of the cost. There is also the IoT side of things where the heart-rate response to media such as news, social media and videos could be used to classify content.

Check out our take on the original hack for capacitive touch imaging as well as using a piezoelectric sensor for the same application.

A Huge Infra-Red Touch Board

We’re all used to touch pads on our laptops, and to touch screens. It’s an expectation now that a new device with a screen will be touch-enabled.

For very large surfaces though, touch is still something of an expensive luxury. If you’re a hardware hacker, unless you are lucky enough to score an exceptional cast-off, the occasional glimpse of a Microsoft PixelSense or an interactive whiteboard in a well-equipped educational establishment will be the best you’re likely to get.

[Adellar Irankunda] may have the answer for your large touch board needs if you aren’t well-heeled, he’s made one using the interesting approach of surrounding the touch area with an array of infra-red LEDs and photo transistors. By studying the illumination of the phototransistors by different LEDs in the array, he can calculate the position of anything such as a pointing finger that enters the space. It’s an old technique that you might have found on some of the earlier touch screen CRT monitors.

His hardware is built on twelve breadboards mounted in a square, upon which sit 144 LED/phototransistor pairs managed through a pile of 4051 CMOS multiplexers by a brace of Arduino Nanos. If you fancy one yourself he’s provided all the code, though the complex array of breadboards to assemble are probably not for the faint-hearted. You can see it in action in a video we’ve posted below the break.

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EL Wire Gets Some Touching After Effects

If you thought glowy wearables have had their time, guess again! After a few years designing on the side, [Josh] and [his dad] have created a nifty feature for EL wire: they’ve made it touch sensitive. But, of course, rather than simply show it off to the world, they’ve launched a Kickstarter campaign to put touch-sensitive El Wire in the hands of any fashion-inspired electronics enthusiast.

El Wire (and tape) are composed of two conducting wires separated by a phosphor layer. (Starting to sound like a capacitor?) While the details are, alas, closed for now, the interface is Arduino compatible, making it wide open to a general audience of enthusiasts without needing years of muscled programming experience. The unit itself, dubbed the Whoaboard, contains the EL Wire drivers for four channels at about 10ft of wire length.

El Wire has always been a crowd favorite around these parts (especially in Russia). We love that [Josh’s] Whoaboard takes a conventional material that might already be lying around your shelves and transforms it into a fresh new interface. With touch-sensitivity, we can’t wait to see the community start rolling out everything from costumes to glowy alien cockpits.

Have a look at [Josh’s] creation after the break!

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Hackaday Prize Entry: Modular, Low Cost Braille Display

A lot of work with binary arithmetic was pioneered in the mid-1800s. Boolean algebra was developed by George Boole, but a less obvious binary invention was created at this time: the Braille writing system. Using a system of raised dots (essentially 1s and 0s), visually impaired people have been able to read using their sense of touch. In the modern age of fast information, however, it’s a little more difficult. A number of people have been working on refreshable Braille displays, including [Madaeon] who has created a modular refreshable Braille display.

The idea is to recreate the Braille cell with a set of tiny solenoids. The cell is a set of dots, each of which can be raised or lowered in a particular arrangement to represent a letter or other symbol. With a set of solenoids, this can be accomplished rather rapidly. [Madaeon] has already prototyped these miniscule controllable dots using the latest 3D printing and laser cutting methods and is about ready to put together his first full Braille character.

While this isn’t quite ready for a full-scale display yet, the fundamentals look like a solid foundation for building one. This is all hot on the heels of perhaps the most civilized patent disagreement in history regarding a Braille display that’s similar. Hopefully all the discussion and hacking of Braille displays will bring the cost down enough that anyone who needs one will easily be able to obtain and use one.

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Biometric Bracelet Electrifies You to Unlock Your Tablet

Researchers [Christian Holz] and [Marius Knaust] have come up with a cool new way to authenticate you to virtually any touchscreen device. This clever idea couples a biometric sensor and low-data-rate transmitter in a wearable wrist strap that talks to the touch screen by electrifying you.

Specifically the strap has electrodes that couple a 50V, 150kHz signal through your finger, to the touchscreen. The touchscreen picks up both your finger’s location through normal capacitive-sensing methods and the background signal that’s transmitted by the “watch”. This background signal is modulated on and off, transmitting your biometric data.

The biometric data itself is the impedance through your wrist from one electrode to another. With multiple electrodes encircling your wrist, they end up with something like a CAT scan of your wrist’s resistance. Apparently this is unique enough to be used as a biometric identifier. (We’re surprised.)

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Is That Google In Your Pants?

Google’s Project Jacquard is tackling the age old gap between controlling your electronic device and touching yourself. They are doing this by weaving conductive thread into clothing in the form of a touch pad. In partnership with Levi Strauss & Co., Google has been designing and producing touch interfaces that are meant to be used by developers however they see fit.

touch-sensitive-jeans-thumbThe approach that Project Jacquard has taken from a hardware standpoint is on point. Rather than having an end user product in mind and design completely towards that goal, the project is focused on the interface as its product. This has the added benefit of endless varieties of textile interface possibilities. As stated in the video embedded after the break, the conductive touch interface can be designed as a visibly noticeable difference in material or seamlessly woven into a garment.

As awesome as this new interface may seem there are some things to consider:

  • Can an unintentional brush with another person “sleeve dial” your boss or mother-in-law?
  • What are the implications of Google putting sensors in your jeans?
  • At what point is haptic feedback inappropriate? and do we have to pay extra for that?

We’ve covered e-textiles before from a conductive thread and thru hole components approach to electro-mechanical implementations.

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inFORM: MIT’s Morphing Table

Have you ever wished your dinner table could pass the salt? Advancements at MIT may soon make this a reality — although it might spill the salt everywhere. Enter the inFORM: Dynamic Physical Affordances and Constraints through Shape and Object Actuation.

While the MIT paper doesn’t go into much detail of the hardware itself, there are a few juicy tidbits that explain how it works. There are 900 individually actuated white polystyrene pins that make up the surface, in an array of 30 x 30 pixels. An overhead projector provides visual guidance of the system. Each pin can actuate 100mm, exerting a force of up to 1.08 Newtons each. To achieve the actuation, push-pull rods are utilized to maximize the dense pin arrangement as seen, making the display independent of the size of the actuators. The actuation is achieved by motorized slide potentiometers grouped in sets of 6 using custom PCBs that are driven by ATMega2560s — this allows for an excellent method of PID feedback right off the actuators themselves. There is an excellent image of the entire system on page 8 of the paper that shows both the scale and complexity of the build. Sadly it does not look like something that could be easily built at home, but hey, we’d love for someone to prove us wrong!

Stick around after the break to see this fascinating piece of technology in action. The video has been posted by a random Russian YouTube account, and we couldn’t find the original source for it — so if you can, let us know in the comments!

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