Reading from a large number of inputs, like this piano keyboard, can be tedious. Even when multiplexing there’s a lot to keep track of. But if you choose the right microcontroller, you may have hardware assistance. Here’s an ATmega640 is using it’s external memory interface to read the key matrix.

You may remember the Open Music Labs article about reading from a shift register using just one pin of a microcontroller. This time around a shift register is still used, but instead of pulling in a long line of parallel inputs, the switches are multiplexed to reduce the number of I/O pins used to read them.

A 74HC573 is used to facilitate the multiplexing. We won’t go into how that part is accomplished; there’s a separate post that explains the process. What’s unique here is that the XMEM peripheral of the AVR microcontroller is used to grab the data. This is intended for external memory chips, but if you get the timing just right, it greatly simplifies reading in a matrix of up to 128 inputs.

When [Dave] installed hardwood flooring in his house, he needed a solution to help automate the monotonous task of routine sweeping. Rather than go out and buy one of the many existing automated sweep robots out there, he decided to use his passion for LEGO Robotics to design and build a NXT based Swifferbot he calls Pulito. His version implements all the important features such as object avoidance using bump sensors, an IR beacon used to automatically return to the charging station, and a photoresistor to monitor the charge of the battery. [Dave] also includes a nifty LEGO sensor multiplexor, allowing him to save on I/O ports, which is almost worth sharing by itself.

Videos after the break.

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Let’s face it, walking around in the rain sucks. [Matth3w] is trying to add a little whimsy to an unpleasant experience by adding an LED matrix to his umbrella. The array contains 80 LEDs that are individually addressable. This is a mutiplexed array that relies on a MIC2981 source driver for the eight rows (or rings in this case), with the ten columns handled by the Arduino. The effect is quite nice as you can see in the video after the break. Now that he’s proven this works, you might want to etch your own PCB in order to get rid of the Arduino board and prototyping shield, making it easier to waterproof the control circuitry. This would make a nice addition to your illuminated umbrella stock.

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Clocks made from blinking LEDs always make for fun projects. [Earthshine] built a clock that displays time abstractly using an 8×8 RGB LED matrix. The video embedded after the break illustrates how to read the time but here’s the gist of it: One LED is illuminated in the outside box of LEDs and moved in a clockwise motion to approximate seconds. Inside of this, there are four quadrants; upper left indicates hour-tens digit, upper right hour-ones, lower left minute-tens, and lower right minute-ones. This certainly makes for an interesting conversation piece!

There is no schematic and no code available but it’s really the concept that we’re interested in. If you must know, [Earthshine] bases this build around an Arduino. A DS1307 real time clock keeps the time, while four 74HC595 shift registers are utilized to control the three LED colors and the multiplexing.

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[Spikenzie] has created an 8×8 LED array that fits inside an ikea frame. He multiplexed the 64 red LEDs on a PCB with connections on the back. He then used a MAX7129, an LED multiplexer and driver, driven by a PIC over SPI to do animations and play pong. He then encased the array in laser-cut cardboard and white acrylic to get large dots. This entire assembly was then placed inside an Ikea RIBBA picture frame. The result is an aesthetic homebrew display that is easy to control.

Related: 64pixels are enough

[punkky] has been documenting his adventures building digital clocks. They each use six 7-segment LED displays, but he’s been gradually changing how they are built. The first version used a CMOS BCD-to-7-sement latch on each display, which is tied to a PIC16F627a. For the next run, he added multiplexing, so he could drive all the segments using just thirteen pins. He’s posted a final schematic with code and details of how the clock timing actually works.

Blinkomat, an LED matrix, turned out quite well. 240 LEDs controlled by an Atmega 16 is what we call a decent bookshelf decoration. The dimensions of 12×20 were chosen due to the fact that the microcontroller has 32 I/O lines.  The LEDs are switched on and off using multiplexing. The brightness, controlled by pulse width modulation can be varied by 16 levels.  The overall effect is quite smooth an fun to look at.  He has programmed it to do other things than just cellular automata.  Our personal favorite is a simple sine wave. Watch it after the break.

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