Scrolling Seven Segment Display Circuit - 16F628

Preview

Many electronic hobbyists are very much interested about build scrolling displays. Most of the time this circuits used matrix displays. However, its cost is high and almost complex to build. Therefore, I try to build a scrolling displays circuit using the seven segments displays because these are cheaper than matrix displays and we can be easily build circuit. This circuit is very simple.

To build this circuit I used PIC16F628A micro-controller and four common cathode seven segment displays. To save micro controller's pin and reduce the cost I used internal oscillator. Massage on ‘scrl_txt’ array will run continuously. You can change the length by changing the value of ‘scrl_len’ according to your text.

A seven-segment LED display is an special arrangement of 7 LED elements to form a rectangular shape using two vertical segments on each side with one horizontal segment on the top, middle, and bottom. By individually turning the segments on or off, numbers from zero to nine and some letters can be display, but we cannot display all characters. However, it is possible to display all the numbers and many characters. See below picture to recognized how seven segment displayed characters.

Seven Segment Characters

In this picture, you can see some characters like K, M, V, W, X and Z cannot displayed properly. If you need to display all the characters then you need to use 14 or 16 segment displays instead of seven segments. To use this type of display you need to modify the firmware and circuit.

Schematic Diagram of Circuit

In Proteus diagram, I used NOT gates to connect the Seven Segment and micro controller. However, in practical you have to use NPN transistor such as 2SC1815 or transistor array IC such as ULN2003 instead of NOT gates. When you are using transistor do not forget to add resistor 1k-10k between micro-controller and base of transistor.

Scrolling Seven Segment