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.

MITx 6.002x wraps up; here’s a review from one of the students

[Jorge] just finished MITx 6.002x with the fine score of 99.1%. Congratulations! We just finished reading through this review of his experience (translate) with the 14-week class and it sounds like the program is extremely well executed. For those that don’t remember, this is an intro to circuits and electronics course offered at the Massachusetts Institute of Technology. Except 6.002x is free to all as an online course (but if you actually want a certificate a fee may be involved).

Above is one of the many screenshots which [Jorge] took of the student web interface. It looks great, and offers pretty much everything you need to complete the class. The textbook, which runs at least $65 for a paper copy, is available through the web interface as part of the course. The labs even include web demos you can use to simulate circuits and probe and measure the resulting signals and wave forms. If you have questions there is access to the teachers, but also a set of forums where you can work with other students.

Perhaps most interesting is [Jorge’s] assessment of the time you will spend working on the class. He thinks that if you’re already familiar with electronics the work can be complete in about one afternoon per week. Scheduling is flexible — tests are available for one week, but once you start taking one it must be completed in 24 hours.

He believes this will be offered again in the fall so keep a look out for registration to begin.

[Thanks Pan]

Reverse engineering an RF clicker

[Travis Goodspeed] has pulled apart a TurningPoint response card, which is an RF device for answering quizzes, attendance checks,  and casting votes in a classroom setting. After tearing it apart, he set out to reverse engineer it and managed to get quite a lot done. At this point he can spoof cards, so he could fake his or several people’s attendance. He can also sniff the packets as they are sent, opening up a plethora of opportunities to mischief. The one that was mentioned in the tip line was to simply repeat the answer that was most often sent for the quizzes. The writeup is very detailed and has great pictures. Good job [Travis].

[thanks Springuin]

SparkFun stencil and solder paste class notes

stencil

Hobby electronics manufacturer SparkFun has started offering various classes at their Boulder, CO facility. [Landon] has been attending as many as possible and posted about his experience during their Stencil and Solder Paste class. Solder paste is used when manufacturing boards with a reflow oven. He took quite a few pictures of the process and posted notes and audio. He says it’s definitely something you’d have to learn hands-on, but his numerous photos give you an idea of what’s involved. Below, you can watch a video of the paste clean-up pass and stencil removal.

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