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LED Scanner(CD4017)

2014-12-11 21:43
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This article briefly describes the LED Scanner (CD4017). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, you can better grasp this principle. In this circuit, you can learn about and purchase these components: CD4017.

Here is a simpleLEDchaser simulating a scanner through the back and forth light effect. It used high bright WhiteLEDs to give the chaser effect. The circuit uses an oscillator to produce fast pulses and a decade counter to drive theLEDs.

IC1 is designed as an astable multivibrator to give continuous positive pulses to the decade counter. Variable resistor VR1, R1 and C1 form the timing components. By adjusting VR1, it is possible to change the speed of the scanningLEDs.

Output pulses from IC1 are fed to the clock input of the decade counter IC2. Resistor R2 keeps the clock input of IC2 low after each positive to negative transitions of input pulses. This is necessary because sometimes the clock input of the decade counter stays positive and does not accept input pulses.

Figure 1 LEDScanner Circuit

All the ten outputs are used in the circuit to drive theLEDs. Diodes D1 through D10 (IN 4148) do the trick of forward and backward chasing effect. Out of the ten diodes, eight diodes form OR gates to direct the outputs of IC2 toLEDs. The remaining two diodes maintain the brightness of the two ungatedLEDs. First six outputs of IC2 works in the straight way to give the running effect.

The diode connected to the pin 5 of IC2 is connected to the cathode of the diode from pin 10 (5thLED). This reverses the running sequence in the backward direction. Output 6 drives the 4thLEDand the process repeats up to the 2ndLEDconnected to output pin2.The reset pin 15 and the Clock inhibit pin 13 of IC2 are connected to ground so that IC2 can run freely.