Random Flashing LED Circuit Diagram

Here is an automatic Ornamental LED lamp for decoration purpose. It automatically switches on in the evening and turns off in the morning. Each string of LED flashes at different rates giving a colorful appearance.

Fig. 1: Image of automatic Ornamental LED lamp

IC CD4060 is used in the circuit to drive the LEDs at different flash rates. CD 4060 is the Oscillator cum binary counter cum frequency divider IC with an inbuilt oscillator based on 3 inverters.

In addition to CD 4060, the circuit is based on following components:

1. Resistors

2. LDR

3. LEDs

4. Music Buzzer

5. 12 V battery

Resistor R2, R3 and capacitor C1 set the basic frequency of the oscillator. In addition to the oscillator, the IC has 14 series connected bistables (Ripple cascade). Internally the oscillator signal is applied to the first bistable which drives the second and so on. Since each bistable divides its input signal by two, a total of 15 signals are available each of half the frequency of the previous one. Ten of these 15 signals are available at the outputs. The IC works off 5-15 volts DC.

Frequency of oscillation is calculated using the formula:

fosc = 1 / 2.5 ( R2.C1) in Hz. Where R2 is the resistor at pin 10 in ohms and C1 is the capacitor at pin 9 in Farads.

LDR is used for automatic switching of the IC. LDR controls the voltage at the reset pin 12 of IC. IC remains off if its reset pin is high and triggers when the reset pin is low. During day time, LDR conducts and the reset pin remains high to inhibit the IC. When the light falling on the LDR ceases in the evening, IC triggers and starts oscillation. Each LED string turns on and off at regular intervals. Since the on/off time of each output is different, the flashing of LEDs gives a beautiful appearance. A Music buzzer can be connected to the last output (long on / off time) to generate music along with the dancing of LEDs.

Use different colors of LED, three in each output. Flashing rate can be varied by changing the value of either R2 or C1