Learn shift registers without involving a microcontroller


This is a truly hands-on approach to learning. [Kevin Darrah] ditched the microcontroller and is using push buttons to learn about 595 shift registers. The test rig uses two of the serial-in, parallel-out chips. These are cascading which means that as data from the first chip overflows it feeds the input of the second. The parts are commonly used to drive LEDs, or reduce the number of pins needed to drive peripherals like this character LCD.

The five push-buttons give you a chance to intuitively learn how the chip logic works. The blank button is also commonly called Output Enable (OE). Driving it high shuts off the outputs of the chips but doesn’t clear the data. That task is performed by the clear button which is driven low to set all of the shift register memory to zero. The other three buttons set the logic level, shift it into the chip using the clock signal, and push the stored values to the outputs using the latch.

To get a visual approximation of what’s happening inside of these chips you should check out the shift register tutorial linked to in this post.

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Animated X-mas sign

Sure, it may be two and a half months until Christmas. That doesn’t mean we can’t start building a few Christmas decorations. Last year, [RB] over at Embedded Lab made an animated Christmas sign using a simple microcontroller setup. This year, [RB] is adding a blinking LED border and doing the entire project with 74xx ICs.

The letters for this year’s sign were recycled from last years’. This time, however, two strings of 12 LEDs are used for the blinking border. The blinking circuitry uses a 74hc14 Schmitt trigger to provide the clock. A pair of 74hc595 shift registers turn each letter on one at a time. The speed is controlled with a small trim pot.

Using ICs to drive a series of lights in a pattern isn’t a new thing – you’d be hard pressed to not find a similar setup in the blinking panels of sci-fi shows of the 60s and 70s. Of course this sign doesn’t compare with what can be done with a microprocessor a lot of patience, it’s still a very nice build. Check out the video after the break to see the X-mas sign in action.

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BlokClok – Abstract time display


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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