This 5-color LED flasher circuit can be built using the popular 555 timer and 4017 decade counter ICs. It does not require any expensive components like a microcontroller.
The timer IC is used as an astable multivibrator to generate a clock pulse, which is fed to the clock input of the 4017. Outputs of the 4017 are connected to bases of five transistors to drive 20 LEDs of different colors, each with its current-limiting resistor.
The 4017 advances to the next output every time it receives a clock pulse, causing the LEDs to turn on and off in sequence. The speed of the flashing can be adjusted by changing the values of the resistors and capacitors in the 555 timer circuit. The author’s prototype is shown in Fig. 1.
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|IC1||-555 IC timer|
|IC2||-4017 decade counter|
|D1-D5||-1N4148 signal diode|
|LED1-LED4||-5mm red LED|
|LED5-LED8||-5mm green LED|
|LED9-LED12||-5mm blue LED|
|LED13-LED16||-5mm white LED|
|LED17-LED20||-5mm yellow LED|
|T1-T5||-BC548 NPN transistor|
|Resistors (all 1/4-watt, ±5% carbon):|
|C1||-100nF ceramic disk|
|C2||-10µF, 25V electrolytic|
|CON1||-2 pin connector|
|-9V or 12V battery|
LED Flasher Circuit Diagram
The circuit diagram of the 5-color flasher is shown in Fig. 2. The circuit comprises a 12V battery (or 12V adaptor), timer IC 555 (IC1), decade counter IC 4017 (IC2), five BC548 transistors (T1 through T5), five sets of 5mm red, green, blue, white, and yellow LEDs each, and a few other components.
If you have built 555 timer-related projects, you would be familiar with the IC. The timer IC’s pin 4 (reset) and pin 8 (Vcc) are connected to the voltage supply, which can be anywhere between 9V and 12V.
In this circuit, a 10k resistor (R1) is connected between Vcc and discharge pin 7 of IC1. A 1k resistor (R2) is connected between pin 7 and the junction of pin 2 (trigger) and pin 6 (threshold).
A 10µF capacitor is connected between pin 6 and the ground pin of the 555 timer, whose ground pin 1 (GND) is connected to the circuit’s ground. A 100nF capacitor is connected between pin 5 (CV) of the timer and the ground. The IC’s out pin 3 is connected to clock pin 14 of IC4017 (IC2).
Pin 16 of the decade counter IC2 is connected to the supply. Its pins 8 (VSS), 13 (CKEN), and pin 15 (Reset) are connected to the ground. The other pins of IC 4017 are outputs used to drive the LEDs for flashing.