Playing Jedi Mind-Tricks On Your TV

Gesture-enabled controls mean you get to live out your fantasy of wielding force powers. It does, however, take a bit of hacking to make that possible. Directly from the team at [circuito.io] comes a hand gesture controller for Jedi mind-trick manipulation of your devices!

The star of the show here is the APDS-9960 RGB and gesture sensor, with an Arduino Pro Mini 328 doing the thinking and an IR transmitter LED putting that to good use. The Arduino Sketch is a chimera of two code examples for IR LEDs and the gesture sensor — courtesy of the always estimable Ken Shirriff, and SparkFun respectively.

Of course, you can have the output trigger different devices, but since this particular build is meant to control a TV the team had to use a separate Arduino and IR receiver to discover the codes for the commands they wanted  to use. Once they were added to the Sketch, moving your hand above the sensor in X, Y or Z-axes executes the command. Voila! — Jedi powers.

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DIY Multi-Touch All The Surfaces

Ever wanted to build a touch table or other touch-input project, but got stuck figuring out the ‘touch’ part? [Jean Perardel] has your back with his multi-touch frame over on IO that makes any surface touch-reactive. In [Jean]’s case, that surface is ultimately a TV inside of a table.

Of course, it’s a bit of a misnomer to say the surface itself becomes touch-reactive. What’s really happening here is that [Jean] is using light triangulation to detect shadows and determine the coordinates of the shadow-casting object. Many barcode scanners and consumer-level document scanners use a contact image sensor (CIS) to detect objects in the path of IR LEDs. These are a low-power, lower-resolution alternative to the CCDs found in high-grade scanners.

As [Jean] explains in the video below, an object placed in the path of a single IR LED facing a sensor array of either type will block the light from reaching the sensors. Keep adding LEDs and their emission angles will begin to overlap, increasing the detection precision. [Jean] reverse engineered a couple of different types of scanners until he found a suitable one. He ended up with CIS that has 2700 light sensors lined up in the space of 20cm (7.87″).

[Jean] designed a 3D-printable frame to hold 96 IR LEDs in stacks of three. A Teensy turns on the LEDs, detects the touch event, calculates the position, and sends those coordinates to a Pi to be displayed on the screen. He eventually went wireless and then built a nice looking touch table to house a 32″ TV.

This is not the only way to build a multi-touch table, nor is it the simplest. Here’s one that uses finger presses to scatter light and an industrial strength projection-based table that was open-sourced a few years ago.

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How To Eclipse When All You Have Is A Welding Helmet

What do you do if you don’t trust cheap eclipse-watching glasses from the internet? What about if everyone’s sold out? Well, if you want to watch the eclipse and you have an auto-darkening welding helmet, you can do what [daniel_reetz] did and hack something together with a remote and your welding helmet to let you see the eclipse without blinding yourself.

Essentially, the hack tricks the helmet’s sensors into thinking it’s very bright. [Daniel_reetz] accomplishes this by gluing a remote with an infrared LED to the side of the helmet and covering it with a 50mm plastic lid. There are two sensors on [daniel_reetz]’s helmet, so he covers the other one with aluminum tape. What this means is that when he presses a button on the remote, the lid-covered sensor thinks it’s very bright out and since the other sensor is covered, it darkens the lens of the mask.

I’m sure some of our readers could come up with a more sophisticated method that would allow you to do something other with your hand than press the remote buttons, but this is a quick and easy hack that’ll get you able to take a quick look at the eclipse – assuming you have a welding mask capable of shading to level 13 or 14. If you are hoping to catch a glimpse of the eclipse, check out the safety guide from NASA just to make sure your eyes are safe. For another method of viewing the eclipse, check out this wearable pinhole camera. For another welding mask hack, check out this augmented reality mask.

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Hackaday Prize Entry: Open-source Pulse Oximetry

Chances are pretty good you’ve had a glowing probe clipped to your fingertip or earlobe in some clinic or doctor’s office. If you have, then you’re familiar with pulse oximetry, a cheap and non-invasive test that’s intended to measure how much oxygen your blood is carrying, with the bonus of an accurate count of your pulse rate. You can run down to the local drug store or big box and get a fingertip pulse oximeter for about $25USD, but if you want to learn more about photoplethysmography (PPG), [Rajendra Bhatt]’s open-source pulse oximeter might be a better choice.

PPG is based on the fact that oxygenated and deoxygenated hemoglobin have different optical characteristics. A simple probe with an LED floods your fingertip with IR light, and a photodiode reads the amount of light reflected by the hemoglobin. [Rajendra]’s Easy Pulse Plugin receives and amplifies the signal from the probe and sends it to a header, suitable for Arduino consumption. What you do with the signal from there is up to you – light an LED in time with your heartbeat, plot oxygen saturation as a function of time, or drive a display to show the current pulse and saturation.

We’ve seen some pretty slick DIY pulse oximeters before, and some with a decidedly home-brew feel, but this seems like a good balance between sophisticated design and open source hackability. And don’t forget that IR LEDs can be used for other non-invasive diagnostics too.

The 2015 Hackaday Prize is sponsored by:

Active “Dart-Sensing” Makes Your Nerf Gun Smarter

When choosing weapons to defend yourself in the next zombie apocalypse, dart jamming whilst firing your Nerf Gun can be a deal-breaker. This clogging is an issue with many “semi-automatic” Nerf Guns. When our trigger-happy fingertips attempt to shoot a dart that hasn’t finished loading into the firing chamber, the halfway-loaded dart folds onto itself and jams the chamber from firing any more darts. The solution, as intended by Nerf, would be to open the chamber lid and manually clear the pathway. The solution, according to [Technician Gimmick], however, is active sensing, and the resulting “smart” dart gun is the TR-27 GRYPHON.

To prevent jamming from occurring altogether, [Technician Gimmick] added a trigger-disable until the dart has fully loaded into the firing chamber. An IR LED, harvested from a mouse scroll wheel, returns an analog value to the microcontroller’s analog-to-digital converter, allowing it to determine whether or not a dart is ready for firing. The implementation is simple, but the results are fantastic. No longer will any gun fire a dart until it has completely entered the chamber.

The TR-27 GRYPHON isn’t just a Nerf Gun that enables “smart” dart sensing. [Technician Gimmick] folded a number of other features into the Nerf Gun that makes it a charmer on the shelf. First, a hall-sensor array identifies the current cartridge loaded into the Nerf Gun and it’s carrying capacity. To display this value and decrement appropriately, [Technician Gimmick] added a dual-seven segment display, a trick we’ve seen before. Finally, a whopping 3S LiPo battery replaces the original alkaline batteries, and the voltage-reducing diodes have been cropped, enabling a full 12.6 Volt delivery to the motors at full charge.

We’re glad to see such a simple trick go such a long way as to almost entirely eliminate Nerf dart jams. For all those braving the Humans-Versus-Zombies frontier this season, may this clever trick keep you alive for just a bit longer.

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An MSP430 Clone Of The Canon RC-1 Remote

For reasons we both agree with and can’t comprehend, most ‘prosumer’ SLR cameras don’t have mechanical shutter releases. Instead, IR LEDs are brought into the mix, the Canon RC-1 remote trigger being the shutter release of choice for people who didn’t choose Nikon. [Vicente] cloned the Canon RC-1, but he didn’t do it to save money; there’s a lot to learn with this project, and making his own allows him to expand it with more features in the future.

Studying the function of the Canon RC-1, [Vicente] found that some compromises needed to be made. The total power emitted by an IR LED is usually a function of its beamwidth; a smaller beamwidth means more photons reaching the IR receiver in the camera. This also means the remote must be aimed at the camera more accurately. In the end, [Vicente] decided on a higher power LED with a tighter beamwidth that’s just slightly below the optimum wavelength for the receiver. It’s all an exercise in compromise, but other components could see similar performance.

With the LED selected, [Vicente] moved on to building the actual controller. He chose an MSP430 microcontroller for its low power consumption, driving the LED with a watch battery and a transistor. Put together on a piece of protoboard, it’s actually pretty close to a TV-B-Gone. With everything soldered up, it’s good enough to trigger his camera’s shutter from about 5 meters away. Future improvements include cleaning up the code, making the timing more accurate with a crystal, and implementing low power mode on the MSP430.

Triple Sensor Mailbox Alert Really Delivers

Messing with the U.S. Mail is not something we generally recommend. But if you build your own mailbox like [Bob] did, you stand a much better chance of doing what you want without throwing up any flags.

Speaking of throwing up flags, one of the coolest parts of this project is the toy mailbox inside the house that monitors the activity of the real box. When there is mail waiting, the flag on the toy mailbox goes up. Once [Bob] retrieves the mail, the flag goes back down automatically. A magnet in the real box’s flag prevents false alarms on the toy box provided the Flag Raised On Outgoing protocol is followed. Best of all, he built in some distress handling: If the mailbox door is left hanging open or the battery is low, the toy mailbox waves its flag up and down.

So, where do the three sensors come in? A magnetic reed switch on the wall of the real mailbox pairs with a magnet in the flag. To determine whether the door is open, [Bob] initially used another magnetic reed switch on the underside of the box. This didn’t work well in wet weather, so he switched to a mechanical tilt sensor. An IR LED on the ceiling and a phototransistor on the floor of the box work together to detect the presence of mail.

[Bob]’s homebrew mailbox has a false back that hides a PIC 16F1825. When the door opens, the PIC wakes up, turns on a MOSFET, and checks the battery level. It waits two minutes for the mailman to do his job and then reads the flag state. After comparing the IR LED and phototransistor’s states, it sends a message to the toy mailbox indicating the presence or absence of mail.

The toy mailbox holds a modified receiver board and a servo to control its flag. [Bob] has made the code and schematics available on his site. Walk-through video is after the jump.

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