Building touch sensors from digital barometer chips

A couple of Harvard researchers have developed a method of using digital barometers as a touch sensor. The good news for us is that they’ve open sourced the project, including Eagle board files, firmware, and details about the materials they used.

The digital barometers were chosen for their characteristics, availability, and low-cost. The sensor uses an array of Freescale MPL115A2 chips, a MEMS Barometer designed for use in altimeters. The mass production makes them cheap (Octopart found some in single quantities for $1.71 at the time of writing). The chips are soldered onto a board which is then cast in rubber. This distributes the force while protecting the sensors. The video after the break shows them standing up to rubber hammer blows and supporting a 25 pound weight.

There are a few tricks to reading the array. The first is that the devices are designed to be used one-to-a-project so they have a fixed i2 address. A separate chip must be used to address them individually. But one it’s up and running you should be able to use it as feedback for the fingertips of that robot arm you’ve been building.

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The many iterations of [Joe’s] PCB business card

[Joe Colosimo] is putting on a show with his PCB business card project. The idea isn’t new, but his goal is to keep it simple and undercut the cost of all other PCB cards he’s seen. This is the third generation of the board design, and he’s just waiting on some solder mask solution before he tries running it through the reflow oven.

The first two prototypes used some through-hole parts. Notably, the battery was to be positioned in a circular cut-out and held in place by a metal strap and some bare wires. But he couldn’t quite get it to work right so this design will transition to a surface-mount strap for one side, and the large circular pad for the other. At each corner of the board there is a footprint for an LED. He tried milling holes in the board to edge-light the substrate. Now he just mounts the LED upside down to give the board a blue glow. The LEDs are driven by an ATtiny10 microcontroller which takes input from the touch sensor array at the bottom right.

He etched a QR code on the board which seems to work better than the milled QR experiments we saw back in April. The link at the top point’s to [Joe’s] main page on the card. Don’t forget to follow the links at the bottom which cover each part of the development more in-depth.

[Thanks Skitchin]

Bananaphone lets you use fruit and other things as switches

We’re used to [Sprite_TM] rolling out his own hacks hot on the heels of new concepts. Now we’re glad to see that [Jeff Ledger] is doing the same thing here. He was inspired by a Kickstarter project which vows to let you use fruit, clay, and a number of other common (but weird for this use) substances to interface with electronic projects. The mess you see above is the Bananaphone, a synthesizer played with touch sensitive bananas. Think of them as keys on a piano.

The interface works by measuring R/C decay. Each banana is connected to its own input pin on the Propeller board. The capacitance of the bananas rise when you touch them, and this results in a longer R/C decay measurement. Calibrate the target decay period, and you’ve got a reliable capacitive touch sensor which also happens to be delicious. Check out the results which [Jeff] achieves in the video after the break.

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Turning anything into a touch sensor

This year at the CHI conference in Austin, [Munehiko Sato], [Ivan Poupyrev], and [Chris Harrison] out of the Disney research lab in Pittsburgh demonstrated their way to make touch sensors out of anything. Not only to they suggest using the surface of your skin to control cell phones and MP3 players, they’re also able to recognize touch gestures, like poking or grasping an object. That sounds a little heady, so check out the video of the Touché tech in action.

Like the capacitive touch sensors in our phones and tablets, Touché measures the rise and fall of a capacitor’s charge over time. Unlike  other touch sensors, Touché scans the capacitor at different rates, allowing for a ‘capacitive profile’ that is used to recognized touch gestures.

The applications for this tech are nearly innumerable; the team demonstrated scolding someone for eating cereal with chopsticks (yeah, we know…), an on-body music player interface, and gestures for an office doorknob that notifies passersby if you’ve stepped out for a minute or are gone for the day.

It’s a very interesting build, and we give it two weeks until someone replicates this build. We’ll be sure to post it then.

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A simple touch interface for Music Player Daemon and more

mpd-controller

[Andrew] recently got the authorization to install Linux on his work PC, and he was looking for a way to control his music without relying on keyboard shortcuts to do so. Additionally, he wanted an unmistakable visual cue when he received messages in Pidgin, so he decided to build an external input/notification box.

The control box, quite literally, is a cardboard box in which [Andrew] crammed some components he got way back when from the crew at Seeed Studio. A Seeeduino serves as the brains of his control panel, interfacing with his PC over USB. He uses a set of 4 touch sensors and a potentiometer to control the MPD, allowing him to easily switch tracks, pause his music, control the volume, and lock his computer with a simple touch. A side-mounted RGB LED lights green to show that the system has received his commands successfully, pulsing a bright blue whenever a message arrives via Pidgin.

While the case isn’t exactly pretty, it is small, recycled, and takes up very little desk space. [Andrew] says that it works great, and he has made his code available on github if anyone is interested in using it.

Touch-based wirless RGB lamp control

[Alex] built an add-on board for his TI launchpad that lets him use it as a wireless controller for an RGB lamp (translated). As you can see above, the board has a pair of female pin-headers which make it easy to install or remove the board. This way you can use it for other projects without any hassle.

The board itself doesn’t have any buttons. Instead, [Alex] etched a two-sided PCB, including pads for use as capacitive touch sensors. Here we only see the underside of the board, which hosts four RGB LED modules. These give feedback by showing the levels which are about to be set for each color. In the clip after the break you’ll get a good look at the touch sensors. There are two that act like buttons, scrolling through each color channel, and sending the updated values to the lamp via a wireless module mounted on that same side. There are also four pads which act as a slider. We didn’t see any code but apparently this uses one of TI’s touch sensor libraries.

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NES controller uses capacitive touch instead of buttons

Here’s one way to really keep the component count low. [David] developed an NES controller that doesn’t use any buttons. The copper clad has been milled to provide a pad which registers a button push based on capacitance. The board has a SIL header at the top, making it easy to plug into the Arduino board that reads the inputs.

[David] had trouble getting the Arduino pin read functions to respond fast enough for he NES console’s expectations. He ended up using commands to access the ATmega’s peripherals directly in order to achieve the target timing. Speaking of, he did his own sniffing of the communication scheme using a logic analyzer. The results of that work, as well as the board files and code are available at the site linked above. And there’s a demo of the controller used to play Super Mario Bros. in the clip after the break.

This is actually a tangential project using a PCB mill which he’s developing through Kickstarter. This certainly shows that the mills works as designed.  Continue reading “NES controller uses capacitive touch instead of buttons”