Arduino Tetris on a Multiplexed LED Matrix

[Alex] needed a project for his microcomputer circuits class. He wanted something that would challenge him on both the electronics side of things, as well as the programming side. He ended up designing an 8 by 16 grid of LED’s that was turned into a game of Tetris.

He arranged all 128 LED’s into the grid on a piece of perfboard. All of the anodes were bent over and connected together into rows of 8 LED’s. The cathodes were bent perpendicularly and forms columns of 16 LED’s. This way, if power is applied to one row and a single column is grounded, one LED will light up at the intersection. This method only works reliably to light up a single LED at a time. With that in mind, [Alex] needed to have a very high “refresh rate” for his display. He only ever lights up one LED at a time, but he scans through the 128 LED’s so fast that persistence of vision prevents you from noticing. To the human eye, it looks like multiple LED’s are lit up simultaneously.

[Alex] planned to use an Arduino to control this display, but it doesn’t have enough outputs on its own to control all of those lights. He ended up using multiple 74138 decoder/multiplexer IC’s to control the LED’s. Since the columns have inverted outputs, he couldn’t just hook them straight up to the LED’s. Instead he had to run the signals through a set of PNP transistors to flip the logic. This setup allowed [Alex] to control all 128 LED’s with just seven bits, but it was too slow for him.

His solution was to control the multiplexers with counter IC’s. The Arduino can just increment the counter up to the appropriate LED. The Arduino then controls the state of the LED using the active high enable line from the column multiplexer chip.

[Alex] wanted more than just a static image to show off on his new display, so he programmed in a version of Tetris. The controller is just a piece of perfboard with four push buttons. He had to work out all of the programming to ensure the game ran smoothly while properly updating the screen and simultaneously reading the controller for new input. All of this ran on the Arduino.

Can’t get enough Tetris hacks? Try these on for size.

Boxing Trainer Uses DIY Force Sensors

A team of Cornell students have designed and built their own electronic boxing trainer system. The product of their work is a game similar to Whack-A-Mole. There are five square pads organized roughly into the shape of a human torso and head. Each pad will light up based on a pre-programmed pattern. When the pad lights up, it’s the player’s job to punch it! The game keeps track of the player’s accuracy as well as their reaction time.

The team was trying to keep their budget under $100, which meant that off the shelf components would be too costly. To remedy this, they designed their own force sensors. The sensors are basically a sandwich of a few different materials. In the center is a 10″ by 10″ square of ESD foam. Pressed against it is a 1/2″ thick sheet of insulating foam rubber. This foam rubber sheet has 1/4″ slits cut into it, resulting in something that looks like jail bars. Sandwiching these two pieces of foam is fine aluminum window screen. Copper wire is fixed the screen using conductive glue. Finally, the whole thing is sandwiched between flattened pieces of corrugated cardboard to protect the screen.

The sensors are mounted flat against a wall. When a user punches a sensor, it compresses. This compression causes the resistance between the two pieces of aluminum screen to change. The resistance can be measured to detect a hit. The students found that if the sensor is hit harder, more surface area becomes compressed. This results in a greater change in resistance and can then be measured as a more powerful hit. Unfortunately it would need to be calibrated depending on what is hitting the sensor, since the size of the hitter can throw off calibration.

Each sensor pad is surrounded by a strip of LEDs. The LEDs light up to indicate which pad the user is supposed to hit. Everything is controlled by an ATMEGA 1284p microcontroller. This is the latest in a string of student projects to come out of Cornell. Make sure to watch the demonstration video below. Continue reading “Boxing Trainer Uses DIY Force Sensors”

Hackin’ the junkyard: Electric scrap bike projects

[Brad Graham] wrote in to let us know about his electric bike data dump over at atomiczombie.com, written just for us! Last we heard from [Brad] he was building some serious robots and freakishly tall tallbikes but since the weather has turned for the chilly its time to focus on indoor projects. Using a combination of robot parts, electrical conduit, and OEM bikes for the frames [Brad] takes us through several of his builds and all the various complications trying to drive the (often very powerful) electric motors. The builds range from scrapping motors and controllers to full blown drop in hub motor systems that can combine human and electric power. There is even an electric pusher cargo cart designed for a cooler, because beers are not going to haul themselves around.

Don’t forget to check out the AtomicZombie website for a ton of useful tips to chopping up bikes for your own mutant transpiration projects, we know we will. Thanks [Brad]!

Win a laser cutter by playing with light

Buildlounge and Full Spectrum Laser have decided to give away a laser cutter to whoever comes up with the best project involving light.

The contest is in part sponsored by  adafruit industries. The focus of the contest is light – just design something around light, submit it, and you’re in the drawing for your own laser cutter. A solar oven, photophone, solar fiber-optic lighting and hacking apart an old overhead projector are suggested on the contest page, but the winning project will probably be much cooler.

Entries are due by January 1st. First prize is Full Spectrum Laser’s 40 Watt laser cutter, second is an awesome green laser pointer from Wicked Lasers, and third prize is an EL wire starter kit from Adafruit. Entries are due by January 1st, so we expect to see a lot of awesome submissions on the Hack A Day tip line between now and New Years.

Hackaday links: January 24, 2011

New Project Hosting site

[Paul] wrote in to tell us about his brand new hack hosting service, HackHut. Based on WordPress with some modifications, it is definitely worth keeping an eye on as new features emerge.

Instructabliss

Speaking of project hosting, Instructables are a common source of projects as well as complaints. Instructabliss by [Daid] is an often mentioned solution in our comments, and we thought we would bring it up so commenters don’t have to. We understand why it was made and think it was a clever hack, but we don’t officially endorse it. We survive on Ad revenue, if someone were doing this to us, it would hurt. We’re also not sure about the legalities of such a service, so keep us updated.

Grass Burning Robot

[Sebastian] brings us his grass burning, flame throwing robot. This robot takes in SVG files to create its burn path, and burns away. Not too many details, but be sure to check out the photos on his site.

[via Make]

Project enclosures the right way

[Stephen Eaton] created an enclosure and shared his process in a pair of blog post. We thought is was amusing that he remarks on how rarely his projects get the to point that you’d want to make an enclosure for them. We’ve certainly got a lot of bare-PCB creations lying around. But when it does come time, we think his fabrication method is a good way to go.

First of all, he didn’t start from scratch. He already had a SparkFun project case sitting around. The problem is figuring how to make it work for your situation. We’ve used a drill, a Dremel, and a file in the past and that yields passable results but nothing that would be mistaken for anything other than a carefully mangled project box. [Stephen] decided to mill the openings he needed from the box, which yielded professional looking results. He started by emailing SparkFun and asking if they could give him a 3D model of the project box and the obliged. He then modeled the LCD screen, LED light pipes, button, USB port, and SD socket. From there it was off to the mill with a custom jig and a few tricks we think you’ll appreciate. The end result is just another reason to build the CNC mill you’ve had on your mind for so long.

Student Soaker, wireless water gun

As far as pranks go, [Austin Shaf’s] wireless hidden water gun is a real treat. The video above goes over a brief explanation and shows the setup in action. The prankster holds onto a wireless AVR remote, and when the unsuspecting victim walks by, he activates a second AVR controlling a pump; spraying water everywhere.

While most of us are out of school by now, the project would still be a fun office or perhaps street prank. If you’re one for registering, schematics and source code can be found at AVRFreaks. Alternatively, check after the jump for a copy of both.

Related: Office Pranks, and Water Guns.

Continue reading “Student Soaker, wireless water gun”