Circuit Diagram of Self-Writing LED Display Sign Controller

The following circuit is a self-writing LED display sign controller. It has eight power shift register which are installed in cascade order. The shift registers are used to charge up a string of 64 lamps or LEDs sequentially. Here is the schematic :

Self-Writing LED Display Sign Controller

Self-Writing LED Display Sign Controller

When the shift register clock (SRCK) is clocked, the register is clocked, so that the display is update after each bit of data is shifted in. The LEDs strobe on from left to right and until the LEDs strobe off in the same mode because of the serial input data (SER IN) is held alternately high and low for any period bigger than 64 clocks. The display sign is active and attractive because the LEDs arranged sequentially as in written message.

This circuit uses LM556 timer to generate the clocks and requires only one IC in addition to the shift register. To blanking or blinking the LEDs, this circuit uses the output enable. [Source: Texas Instruments Application Report]