What’s the Cheapest Way to Scan Lots of Buttons?

So you’re building a new mechanical keyboard. Or attaching a few buttons to a Raspberry Pi. Or making the biggest MIDI grid controller the world has ever know. Great! The first and most important engineering question is; how do you read all those buttons? A few buttons on a ‘Pi can probably be directly connected, one for one, to GPIO pins. A mechanical keyboard is going to require a few more pins and probably some sort of matrix scanner. But the grid controller is less clear. Maybe external I/O expanders or a even bigger matrix? Does it still need diodes at each button? To help answer these questions the folks at [openmusiclabs] generated a frankly astounding map which shows, given the number of inputs to scan and pins available, which topology makes sense and roughly how much might it cost. And to top it off they link into very readable descriptions of how each might be accomplished. The data may have been gathered in 2011 but none of the fundamentals here have changed.

How do you read this chart? The X axis is the number of free pins on your controller and the Y is the number of I/Os to scan. So looking at the yellow band across the top, if you need to scan one input it always makes the most sense to directly use a single pin (pretty intuitive, right?). Scrolling down, if you need to read 110 inputs but the micro only has eight pins free there are a couple choices, keys E and F. Checking the legend at the top E is “Parallel out shift register muxed with uC” and F is “Parallel in shift register muxed with uC“. What do those mean? Checking the table in the original post or following the link takes us to a handy descriptive page. It looks like a “parallel out shift register” refers to using a shift register to drive one side of the scan matrix, and “parallel in shift register” refers to the opposite.

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E-Dermis: Feeling At Your (Prosthetic) Fingertips

When we lose a limb, the brain is really none the wiser. It continues to send signals out, but since they no longer have a destination, the person is stuck with one-way communication and a phantom-limb feeling. The fact that the brain carries on has always been promising as far as prostheses are concerned, because it means the electrical signals could potentially be used to control new limbs and digits the natural way.

A diagram of the e-dermis via Science Robotics.

It’s also good news for adding a sense of touch to upper-limb prostheses. Researchers at Johns Hopkins university have spent the last year testing out their concept of an e-dermis—a multi-layer approach to expanding the utility of artificial limbs that can detect the curvature and sharpness of objects.

Like real skin, the e-dermis has an outer, epidermal layer and an inner, dermal layer. Both layers use conductive and piezoresistive textiles to transmit information about tangible objects back to the peripheral nerves in the limb. E-dermis does this non-invasively through the skin using transcutaneous electrical nerve stimulation, better known as TENS. Here’s a link to the full article published in Science Robotics.

First, the researchers made a neuromorphic model of all the nerves and receptors that relay signals to the nervous system. To test the e-dermis, they used 3-D printed objects designed to be grasped between thumb and forefinger, and monitored the subject’s brain activity via EEG.

For now, the e-dermis is confined to the fingertips. Ideally, it would cover the entire prosthesis and be able to detect temperature as well as curvature. Stay tuned, because it’s next on their list.

Speaking of tunes, here’s a prosthetic arm that uses a neural network to achieve individual finger control and allows its owner to play the piano again.

Thanks for the tip, [Qes].

Hacking An Industrial 42″ Multitouch PC

We’re slowly moving in the direction where everyone will have a touch screen desk like in the 1982 TRON movie or in the 1987 Star Trek: The Next Generation series with its ubiquitous touchscreen starship controls. [FFcossag] lucked into that future when a local company offered him an industrial 42″ multitouch PC that they were throwing out. A few hacks later and he has us all suitably envious.

Before hacking away though, he had to take care of some magic smoke. The source of this turned out to be yellow goop on the PC’s power supply that had turned conductive across a resistor. Cleaning it fixed the problem.

Moving on to the hacks, he added brightness control by using a potentiometer to control the power to the backlight. Be sure to watch carefully in the video below where he’s attaching a magnet and cord to the potentiometer, and encasing it all in epoxy. At that point, we’re pretty sure we see him spin up a hard drive platter with a sandpaper disk attached to it, forming a bench top disc sander and making us like this hack even more.

He also replaced a small speaker with a larger speaker and amplifier, giving a volume and sound quality difference that’s like night and day. He also added a breakout board with relays for power management, eliminating a seven watt continuous draw when in standby mode.

Be sure to watch the video to the end where he leaves us with a tour of the hacked interior hardware. We like how he’s labeled all his handiwork for any future hacker who might open it up

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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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