A modular 7 segments display

The serial 7 segments display

I have a bunch of vintage red seven segment led display. This kind of display is quite pin consuming. Even with multiplexing, the number of control is huge if the goal is to interface it with low range microcontrollers.
The solution is not new: use a shift register. The principle is to control the display with four wires:

  •   Vcc
  •   Ground
  •   Shift in clock
  •   Data in

To get a simple module, I developed a tiny PCB to plug in the Led display and at the back of it the shift register with current limitation resistors. The challenge is to fit all these components on such small area, and to get these modules stackable. Then, it allows building a one to N seven segments display. Only few changes are expected in the microcontroller code.
To do so, I chose:

  •   74HC164: For the shift register, in SOIC16. The output current is rated over 20 mA, a sufficient value in this application. This version works properly down to 2V, so the modules can be used in 3.3V applications.
  •   150 ohms resistors: for current limitation. The package is 0805.

The Schematic and PCB The schematic consist in few components:

sch_s7seg

The PCB required that the right side must connect to the left to propagate the data and the clock. It is so tiny that I don’t succeed to propagate the shift clock through the single layer. So a small strap over the shift register is needed. The results:

Image

Application: a minimal voltmeter

Six bricks of this display and one ATtiny13A are needed.

  • PB2 : serial 7 segment clock
  • PB4 : serial 7 segment data
  • PB3 : ADC input

The breadboard is very noisy due to bad contacts, but the result is good enough for the example. The value is displayed in millivolts:

s7seg_adc

The complete frame is executed in less than 200µs with an internal ATtiny frequency of 9.6 MHz.

NewFile0

Material

Schematic and PCB (KiCAD)

C Atmel Studio Project

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12 thoughts on “A modular 7 segments display

  1. Pingback: Lots of seven segment displays with a single ATtiny

  2. Pingback: rndm(mod) » Lots of seven segment displays with a single ATtiny

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  5. Pingback: Lots of seven segment displays with a single ATtiny | { Codeholics }

  6. Pingback: Lots of seven segment displays with a single ATtiny | OPPATEC

  7. Hi there!
    Nicely work! Is there any noticeable flickering during the segments update/shifting?
    Greetings from Romania!

  8. I see a way to take the data signal between modules without using wires. You can go around the display on the top side. To connect top and bottom grounds, you can use the internal connection inside the display.

  9. Pingback: One Atmel ATtiny13A drives seven-segment LED displays | Bits & Pieces from the Embedded Design World

  10. Pingback: Lots of seven segment displays with a single ATtiny | Make, Electronics projects, electronic Circuits, DIY projects, Microcontroller Projects - makeelectronic.com

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