Lots of seven segment displays with a single ATtiny

7seg

These days they’ve been replaced with character LCD displays or even brightly colored graphical displays, but if you’re trying to display data on one of your projects, there’s nothing like the classic red glow of a red seven segment display. [five volts] got his hands on a few ancient segmented displays, but controlling even one took up more microcontroller pins than he was ready to spare. The solution to this problem was to use a shift register and control multiple segment displays with an 8 pin microcontroller.

[volts] is using an ATtiny13 to control six seven segment displays. Each display is mounted on a hand-etched board, with a shift register and a handful of resistors soldered to the back. By having the microcontroller shift bits down the line, [volts] created an extremely easy to interface 6-digit segment display, and the entire device can be expanded even more.

The board files and schematics are available on [volt]‘s project page. A great project if you’re just starting out to etch your own boards.

Comments

  1. Arlet says:

    With a plain shift register, you’ll get unwanted segments flashing up when the display changes. A better device would be the 74595 which is a shift register with an extra output latch that allows you to cleanly switch all outputs at the same time..

  2. LordNothing says:

    meh, i was able to drive 10 digits with just a 2313, 74hc238, and a 74hc595. though i still need to make my serial interface code a little bit smaller to fit into the 2313’s, tiny flash.

    http://s213.photobucket.com/user/Emperor_of_Nihil/slideshow/SevenSeg

  3. Sweeney says:

    Or just use a single MAX7219 7 segment LED driver chip that covers constant current and 8 digits.

  4. TechMike says:

    Yeah. The MAX7219 is so much easier to deal with. SPI input. Cascade up to 255 parts (I think). Way easier than putzing around with some shift registers. Your time is worth something. Can’t get that back.

    • Agent24 says:

      I’d rather buy some 595s at a few cents each locally than have to order in a MAX7219 from Digikey and pay $50 shipping to my country. Not everyone lives in USA.

      • Sweeney says:

        eBay is your friend. You can pick up MAX7219s for about 70-80 us cents each, including postage. Add the fact that you only need a single resistor and its cheaper than using shift registers.

        • Drone says:

          Widely reported those MAX7219’s on ebay are Chinese fakes. I live in the 3rd World, getting fancy parts is nearly impossible – I wish more understood this.

          • Hatchback says:

            I’ve got a few for about a euro and a half a pop from ebay. For fakes they work quite damn well.

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