A Pair of Projects to Scare the Trick-or-Treaters

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The countdown is on! There’s only a few days left until Halloween, and if you’re still looking for something to spice up the experience for the kids heading to your door, [MagicWolfi] has just what you need. He’s put together two motion-sensing projects that are sure to startle any trick-or-treater.

The first project is a chain of LED-lit pumpkins that are activated by a motion sensor. A set of inverters paired with RC delay lines light up the pumpkins sequentially. They are arranged almost like a strand of Christmas lights and are powered by AA batteries, so in theory they could be expanded to make a strand as long as needed. The project was inspired by a motion-sensing dress and works pretty well as a Halloween decoration!

9378581414283863206[MagicWolfi] is pairing the LED pumpkins with his second project which uses another motion sensor to play scary sound effects. Dubbed the Scare-o-Matic, this device uses a 45-millimeter speaker connected to a SparkFun microSD audio module to produce the scary sound effects. Each time it is triggered it plays a different sound from the list. There are videos and schematics for each of these projects on the project sites if you are interested in recreating any of these before Friday!

Simple POV Bike Effects with WS2811 Strips

Bike Persistance of Vision

[Andrew] wrote in with a new take on the classic persistence of vision bike spoke hack. While many of these POV setups use custom PCBs and discrete LEDs, [Andrew]‘s design uses readily available off-the-shelf components: WS2811 LED strips, an Arduino, an Invensense IMU breakout board, and some small LiPo batteries.

[Andrew] also implemented a clever method of controlling his lights. His code detects when the rider taps the brakes in certain patterns, which allows changing between different light patterns. He does note that this method isn’t incredibly reliable due to some issues with his IMU, so now he senses when the rider taps on the handlebars as well.

If you want to build your own bike POV setup, you’re in luck. [Andrew] wrote up detailed instructions that outline the entire build process. He also provides links to sources for each part to make building your own setup even easier. His design is pretty affordable too, coming in at just under $50 per wheel. Check out a video of [Andrew]‘s setup in action after the break.

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Simple LED Project to Spice Up Your Halloween Party

jackolantern

[Paul's] project is a great example of how you can take a simple project and turn it into something more interesting. He built himself a jack-o-lantern with an Internet controlled RGB LED embedded inside.

[Paul] first wired up an RGB LED to a Raspberry Pi. He was sure to wire up each color using a 100ohm resistor to prevent the LED from burning out. The web interface was written in Python. The interface is pretty simple. It consists of three text fields. The user enters a value between 0 and 255 for each of the three LED colors. The program then lights up the LED accordingly.

[Paul] realized he would need a diffuser for the LED in order to really see the blended colors properly. Instead of using a common solution like a ping-pong ball, he opted to get festive and use a plastic jack-o-lantern. [Paul] removed the original incandescent bulb from the lantern and mounted the LED inside instead. The inside of the pumpkin is painted white, so it easily diffuses the light. The result is a jack-o-lantern that glows different colors as defined by his party guests. Be sure to check out the demonstration video below.

MacGyvered Optoisolator is a Great Introduction

DIY Optoisolator

Sometimes the best way to learn about a technology is to just build something yourself. That’s what [Dan] did with his DIY optoisolator. The purpose of an optoisolator is to allow two electrical systems to communicate with each other without being electrically connected. Many times this is done to prevent noise from one circuit from bleeding over into another.

[Dan] built his incredibly simple optoisolator using just a toilet paper tube, some aluminum foil, an LED, and a photo cell. The electrical components are mounted inside of the tube and the ends of the tube are sealed with foil. That’s all there is to it. To test the circuit, he configured an Arduino to send PWM signals to the LED inside the tube at various pulse widths. He then measured the resistance on the other side and graphed the resulting data. The result is a curve that shows the LED affects the sensor pretty drastically at first, but then gets less and less effective as the frequency of the signal increases.

[Dan] then had some more fun with his project by testing it on a simple temperature controller circuit. An Arduino reads a temperature sensor and if the temperature rises above a certain value, it turns on a fan to cool the sensor off again. [Dan] first graphed the sensor data with no fan hooked up. He only used ambient air to cool things down. The resulting graph is a pretty smooth curve. Next he hooked the fan up and tried again. This time the graph went all kinds of crazy. Every time the fan turned on, it created a bunch of electrical noise that prevented the Arduino from getting an accurate analog reading of the temperature sensor.

The third test was to remove the motor circuit and move it to its own bread board. The only thing connecting the Arduino circuit to the fan was a wire for the PWM signal and also a common ground. This smoothed out the graph but it was still a bit… lumpy. The final test was to isolate the fan circuit from the temperature sensor and see if it helped the situation. [Dan] hooked up his optoisolator and tried again. This time the graph was nice and smooth, just like the original graph.

While this technology is certainly not new or exciting, it’s always great to see someone learning by doing. What’s more is [Dan] has made all of his schematics and code readily available so others can try the same experiment and learn it for themselves.

NYC Maker Faire: The Logistics of Manufacturing Pentagons

Most of the Maker Faire attendees have spent weeks or months putting together their projects. [Matt] is doing things a little differently. He brought two thousand boards, each containing twelve pentagon PCBs with individually addressable LEDs mounted in the center. This weekend, he, his team, and anyone else who can wield a soldering iron will be assembling these pentagon panels into a gigantic glowing crystal.

Last year, [Matt] put together a Kickstarter for Blinkytape, a WS2812 LED strip with an Arduino on one end of the strip to generate patterns of colors. This year, [Matt] is moving into three dimensions with a system of pentagons with a single RGB LED mounted in the center. The pentagons can be soldered together into a regular polyhedra or a convoluted wall of LEDs that form a geometric crystal pattern of blinkyness. The Kickstarter for the BlinkyTile should be up before the faire is over.

[Matt] has a few tips for anyone wanting to run their own Kickstarter: don’t have a lot of SKUs. [Matt] only has to keep track of a single panel of twelve pentagons. Compare this to other failed Kickstarters with dozens of options, several colors, and a few stretch goals, and you quickly see why many, many Kickstarters fail. [Matt] is just selling one thing.

LEDs Turn This Paper Map into a Tram Tracker

Subway radar

Public transit can be a wonderful thing. It can also be annoying if the trains are running behind schedule. These days, many public transit systems are connected to the Internet. This means you can check if your train will be on time at any moment using a computer or smart phone. [Christoph] wanted to take this concept one step further for the Devlol hackerspace is Linz, Austria, so he built himself an electronic tracking system (Google translate).

[Christoph] started with a printed paper map of the train system. This was placed inside what began as an ordinary picture frame. Then, [Christoph] strung together a series of BulletPixel2 LEDs in parallel. The BulletPixel2 LEDs are 8mm tri-color LEDs that also contain a small controller chip. This allows them to be controlled serially using just one wire. It’s similar to having an RGB LED strip, minus the actual strip. [Christoph] used 50 LEDs when all was said and done. The LEDs were mounted into the photo frame along the three main train lines; red, green, and blue. The color of the LED obviously corresponds to the color of the train line.

The train location data is pulled from the Internet using a Raspberry Pi. The information must be pulled constantly in order to keep the map accurate and up to date. The Raspberry Pi then communicates with an Arduino Uno, which is used to actually control the string of LEDs. The electronics can all be hidden behind the photo frame, out of sight. The final product is a slick “radar” for the local train system.

Driving WS2812B Pixels, With DMA Based SPI

WS2812 at 670 kHz

Typically bit-banging an I/O line is the common method of driving the WS2812B (WS2811) RGB LEDs. However, this ties up precious microcontroller cycles while it waits around to flip a bit. A less processor intensive method is to use one of the built-in Serial Peripheral Interface (SPI) modules. This is done using specially crafted data and baud rate settings, that when shifted out over the Serial Data Out (SDO) pin, recreate the needed WS2812B signal timing. Even when running in SPI mode, your hardware TX buffer size will limit how many pixels you can update without CPU intervention.

[Henrik] gets around this limitation by using peripheral DMA (Direct Memory Access) to the SPI module in the Microchip PIC32MX250F128B microcontroller. Once properly configured, the DMA controller will auto increment through the defined section of DMA RAM, sending the pixel data over to the SPI module. Since the DMA controller takes care of the transfer, the micro is free to do other things. This makes all of DMA memory your display buffer. And leaves plenty of precious microcontroller cycles available to calculate what patterns you want the RGB LEDs to display.

Source code is available at the above link for those who would like to peruse, or try it out. This is part of [Henrik's] Pixel Art Project. Video of DMA based SPI pixels after the break:

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