Running Message Display
Light emitting diodes are advan- tageous due to their smaller size, low current consumption and catchy colours they emit. Here is a running message display circuit wherein the letters formed by LED arrangement light up progressively. Once all the letters of the message have been lit up, the circuit gets reset. The circuit is built around Johnson decade counter CD4017BC (IC2). One of the IC CD4017BEs features is its provision of ten fully decoded outputs, making the IC ideal for use in a whole range of sequencing operations.
In the circuit only one of the outputs remains high and the other outputs switch to high state successively on the arrival of each clock pulse. The timer NE555 (IC1) is wired as a 1Hz astable multivibrator which clocks the IC2 for sequencing operations. On reset, output pin 3 goes high and drives transistor T7 to on state. The output of transistor T7 is connected to letter W of the LED word array (all LEDs of letter array are connected in parallel) and thus letter W is illuminated. On arrival of first clock pulse, pin 3 goes low and pin 2 goes high. Transistor T6 conducts and letter E lights up.