This is a running message display circuit wherein the letters formed by the LED arrangement
light up progressively. Once all the letters of the message have been lit up,
the circuit gets reset.
The circuit is built CD4017BC counter menggukan decades. One of the CD4017BE's 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 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 and
thus letter 'W' is illuminated.
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On arrival of first clock pulse, pin 3 goes low and pin 2 goes high. Transistors 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 each successive pulse, the other letters of the display are also illuminated
and finally the complete word becomes visible.