Saturday, December 2, 2023

555 Timer based 5-Colour LED Flasher Circuit

S.C. Dwivedi

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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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555 Timer based LED Flasher
Fig.1. 555 Timer-based LED Flasher

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Required Components

Parts List
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):
R1 -10-kilo-ohm
R2-R12 -1-kilo-ohm
C1 -100nF ceramic disk
C2 -10µF, 25V electrolytic
CON1 -2 pin connector
  -9V or 12V battery
  -Jumper wires

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.

555 Timer LED Flasher Circuit
Fig. 2: Circuit diagram

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.


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  1. Hello,
    May I ask what is the purpose of those diode 1N4148?
    If it has purpose for reversed current, so I would think that both of the outputs Q1 & Q2,etc… connect to the Anode of the diode.
    Please advice,

  2. We thank the reader for detecting this error and sharing with everyone!
    Please refer the circuit diagram and connect anodes of 1N4148 diodes to
    the outputs of Q1, Q3, Q5, Q7, and Q9—just like the connections to Q0,
    Q2, Q4, Q6, and Q8—and the cathodes of 1N4148 diodes to the junctions
    before the base bias resistors of respective transistors. Yes, these diodes are
    for preventing reversed current.

  3. I am using a simulator to simulate this timer circuit but that simulator decade counter is different than this. Decade counter available in simulator is “74HC4017”. Can you specify the difference because i tried but it didn’t work.

  4. The CD4017 and 74HC4017 are decade counters.They have some differences between them.

    1.Technology: The CD4017 is built using CMOS, while the 74HC4017 is CMOS (HC).
    2.Voltage Levels: The CD4017 operates at voltage range from 3V to 18V, while 74HC4017 operates at voltage range 2V to 6V.
    3.Power Consumption: Due to the difference in technology, the CD4017 generally consumes more power compared to the 74HC4017.
    4.Output Current: The CD4017 can provide higher output current than the 74HC4017.
    5.The pinout and functionality of the CD4017 and 74HC4017 are similar, but the differences mentioned above should be considered when selecting the appropriate IC for your specific project.


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