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  • LED Chaser

  • Created: Jun 26, 2015

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Summary

This circuit is a simple LED chaser that uses 74HC4017DB and 555 timer to create a running light sequence.The LEDs will light one at a time for a period of 1 second and the cycle repeats, displaying a running lights. The74HC4017BQ is a 5-stage Johnson decade counter with 10 decoded outputs (Q0 to Q9), an output from the most significant flip-flop (Q5-9), two clock inputs (CP0 and CP1) and an overriding asynchronous master reset input (MR). In addition, the 555 precision timer is capable of producing accurate time delays or oscillation where the duty cycle can be controlled independently with two external resistors and a single external capacitor.

The NE555 timer is the popular timer IC wired in the Astable Multivibrator mode where resistors R1, variable resistor R4 and capacitor C1 act as the timing components. The output pulses are available from the output pin 3 of the timer. These pulses are fed to the input pin 14 of the Johnson decade counter IC 74HC4017DB. Out of the 10 outputs of IC2, eight outputs are used to drive the LEDs. The ninth output ,pin 9 is connected to the reset pin 15 to stop the counting. With the value of C1, each LED remains on for 1 second. When one LED turns off, the second will turn on and so on. This cycle repeats giving the running light appearance. Resistor R3 keeps the input pin 14 of the decade counter low after each pulse. Moreover, the variable resistor can be adjusted to vary the speed of LED chasing.

LED Chaser can be used as an accessory to automobiles considerably to bicycles that does not often have front lights. This can warn other vehicles especially when travelling at night. Furthermore, this may be used as christmas lights displays that are exceptionally captivating or can be integrated to LED signages for auxiliary attraction.

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