A Power Switch for the Chromecast

Chromecasts are fantastic little products, they’re basically little HDMI sticks you can plug into any monitor or TV, and then stream content using your phone or computer as the controller. They are powered by a micro USB port in the back, and if you’re lucky, your TV has a port you can suck the juice off. But what if you want to turn it off while you use a different input on your TV so that your monitor will auto-sleep? You might have to build a power switch.

Now in all honesty, the Chromecast gets hot but the amount of power it draws when not in use is still pretty negligible compared to the draw of your TV. Every watt counts, and [Ilias] took this as an opportunity to refine his skills and combine a system using an Arduino, Bluetooth, and Android to create a robust power switch solution for the Chromecast.

The setup is rather simple. An HC-05 Bluetooth module is connected to an Attiny85, with some transistors to control a 5V power output. The Arduino takes care of a bluetooth connection and uses a serial input to control the transistor output. Finally, this is all controlled by a Tasker plugin on the Android phone, which sends serial messages via Bluetooth.

All the information you’ll need to make one yourself is available at [Ilias’] GitHub repository. For more information on the Chromecast, why not check out our review from almost three years ago — it’s getting old!

Running Calculus on an Arduino

It was Stardate 2267. A mysterious life form known as Redjac possessed the computer system of the USS Enterprise. Being well versed in both computer operations and mathematics, [Spock] instructed the computer to compute pi to the last digit. “…the value of pi is a transcendental figure without resolution” he would say. The task of computing pi presents to the computer an infinite process. The computer would have to work on the task forever, eventually forcing the Redjac out.

Calculus relies on infinite processes. And the Arduino is a (single thread) computer. So the idea of zeno_03running a calculus function on an Arduino presents a seemingly impossible scenario. In this article, we’re going to explore the idea of using derivative like techniques with a microcontroller. Let us be reminded that the derivative provides an instantaneous rate of change. Getting an instantaneous rate of change when the function is known is easy. However, when you’re working with a microcontroller and varying analog data without a known function, it’s not so easy. Our goal will be to get an average rate of change of the data. And since a microcontroller is many orders of magnitude faster than the rate of change of the incoming data, we can calculate the average rate of change over very small time intervals. Our work will be based on the fact that the average rate of change and instantaneous rate of change are the same over short time intervals.

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Precision CNC Drawing with EtchABot

Turning the classic toy Etch-A-Sketch into a CNC drawing tablet intrigues a large number of hackers. This version by [GeekMom] certainly takes the award for precision and utility. Once you build something like this, you can hardly stop writing firmware for it; [GeekMom] produced an entire Arduino library of code to allow joystick doodling, drawing web images, and a self-erasing spirograph mode. The topper is the version that runs as a clock!

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The major hassle with making a CNC version of this toy is the slop in the drawing mechanism. There is a large amount of backlash when you reverse the drawing direction. If that isn’t bad enough, the backlash is different in the vertical or horizontal directions. Part of [GeekMom’s] presentation is on how to measure and correct for this backlash.

The EtchABot uses three small stepper motors. Two drive the drawing controls and the third flips the device forward to erase the previous drawing. The motors are each controlled by a ULN2003 stepper motor drivers. An Arduino Uno provides the intelligence. Optional components are a DS3231 Real Time Clock and a dual axis X-Y joystick for the clock and doodling capability. Laser cut wood creates a base for holding the Etch-A-Sketch and the electronics.

The write up and details for this project are impressive. Be sure to check out the other entries in [GeekMom’s] blog. Watch the complete spirograph video after the break.

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The Smallest Google Street View in Miniatur Wunderland

The world’s largest model railway exhibit — on display in Germany of course — is quite the attraction. The huge Miniatur Wunderland features towns and trains from Germany, Switzerland, Austria, and even a little America. And it’s all on Google Maps.

[Frank] accepted the challenge to build a tiny Google Streetview train, capable of traversing the entire Wunderland. It features a fish-eye camera on both the front and rear car, and is powered by an Arduino — the Wattuino Nanite 85. He upgraded the train to use tiny stepper motors to allow for precise movement along the tracks to get all the shots in perfect Streetview fashion.
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Add Seinfeld Bass Riffs to Any Doorway

It’s not the most involved hack we’ve seen this week, but it’s definitely creative and made us laugh. [Grant] and some friends were joking around about how cool it would be to have sitcom-style entry music fire off every time someone came in through a door, but in real life. You know, like everyone wants to have their own theme music? This is the same idea, but the Seinfeld equivalent. (Video embedded below the break.)

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A few simple parts later (Arduino, MP3 shield, magnetic door reed switch) and a tiny bit of code to randomize which bass riff plays, and it’s a done deal. Like we said, it’s not rocket science, but it’s a humorous addition to what looks like a well-stocked game room. (Is that a Joust console we see?)

For even greater comic effect, why not add Seinfeld bass riffs to your skateboard ramps?

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StarMAT greets visitors with the Imperial March

Strong is the Force, with this Padawan. To coincide with the latest installment of the continuing saga from a galaxy far, far away, [Rohit Gupta] built a Star-Wars themed interactive doormat. The doormat detects a footstep using capacitive sensing and plays a random Star Wars audio clip like the opening theme or the Imperial March or a famous phrase from the movie. Check out the video below the break.

The current setup is temporarily breadboarded, but we are sure it will be popular enough with his visitors to make him tidy it up. The hardware consists of an Arduino with an audio shield connected to a pair of speakers. A capacitive wire loop under the mat and a capacitive sensor tuned to the mat size wire take care of the sensing.

When Earth people step on the mat, the sensor triggers the Arduino to play a random audio clip from the SD card. The capacitive sensing is taken care by the TP223 1-key touch pad detector chip (PDF), which he mounted on a home etched board with SMD parts. The whole bundle is powered by a small “power bank” battery pack like the ones used to charge mobile phones.

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Nixie Tube Energy Meter Dresses up Front Hall

When you move into a new house, there’s always something that needs fixing up. A bit of paint and some new drapes may help freshen up the place and put your mark on it, but things like exposed wiring and a very utilitarian looking electrical panel in your front hall are altogether different. Unwilling to live with the mess, [John Whittington] decided to enclose his utility panel and add a Nixie tube IoT watt meter to dress things up while monitoring energy usage.

IMG_8991-e1451227735242Looking at the “before” pictures on [John]’s blog, we can see why he’d want to invest the effort – not exactly an attractive way to greet guests at the front door. A simple wooden box to replace the previous cover would have sufficed, but why pass up the opportunity to add value? [John] opted for a Nixie tube display to complement the glass of the electric meter. The Nixie modules were a bit on the pricey side, though, so with only a pair of tubes to work with, [John] came up with a clever system to indicate the scale of the display. We doubt he’ll ever see megawatt-level instantaneous power draw, but the meter is also capable of totalling energy use, and as a bonus an ESP-8266 gives lets him stream data to the web.

We’ve featured tons of Nixie projects before – everything from clocks to cufflinks. We have to agree that [John]’s Nixie project turned out great, and it’s sure to be a conversation starter with arriving guests.

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