Running Message Display circuit diagram
Saturday, April 30, 2011
Running Message Display circuit diagram
Light emitting diodes are advan- tageous due to their smaller size, low present consumption and catchy colours they emit. Here is really a running message display circuit wherein the letters formed by LED arrangement light up progressively. As soon as all the letters of the message have been lit up, the circuit gets reset. The circuit is built around Johnson decade counter CD4017BC (IC2). Among the IC CD4017BE’s features is its provision of ten fully decoded outputs, creating the IC ideal for use in a whole range of sequencing operations. In the circuit only one of the outputs remains high as well as the other outputs switch to high state successively on the arrival of each and every clock pulse. The timer NE555 (IC1) is wired as a 1Hz astable multivibrator which clocks the IC2 for sequencing operations. On reset, output pin three 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 therefore letter ‘W’ is illuminated. On arrival of initial clock pulse, pin three goes low and pin 2 goes high. Transistor T6 conducts and letter ‘E’ lights up. The preceding letter ‘W’ also remains lighted because of forward biasing of transistor T7 via diode D21. In a similar fashion, on the arrival of every successive pulse, the other letters of the display are also illuminated and lastly the total word becomes visible. On the following clock pulse, pin 6 goes to logic 1 and resets the circuit, along with the sequence repeats itself. The frequency of sequencing operations is controlled with the assist of potmeter VR1.
