Here's a circuit to build a led based running display using easily available general purpose timer IC NE555 and a popular decade counter IC CD4017. This display consist of 24 LED's of four layers. The NE555 is wired as an astable multivibrator whose output triggers CD4017 counter.
On powering up the circuit, timer starts oscillates to produce triggering pulses. This pulses trigger counter IC and it counts from 0 to 5. These outputs are fed to general purpose NPN transistors BC547 which are used as current drivers for each led layer. As each of the counter output goes hih, the curresponding led layer glows sequentially. After it counts upto 6 values, resets to zero and the process repeats.
How to display custom words using this circuit.
Suppose you want to display ‘STAR.’ Build letter S with L1,T with L2, A with L3 and R with L4.When the circuit is switched on, letter S glows first. Then S and T glow sequentially,followed by S, T and A, and thenS, T, A and R. When Q4 and Q5 outputs of the counter gohigh, the completeword ‘STAR’ glows.Thereafter, letter ‘S’glows again and the cycle repeats.
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