Simple Astable 555 Timer IC Flasher

To achieve a lower parts count than the two-transistor multivibrators, two LEDs can be alternately flashed using a 555 integrated circuit configured as illustrated in Schematic 2. A combination of a 2.2kΩ and a 47kΩ resistor is used to determine the oscillation frequency along with a 10µF capacitor connected to pins 2 and 6. The 47kΩ resistor value can be adjusted between 10kΩ and 100kΩ or more; a greater resistance results in a lower flashing speed. For a variable speed version, a potentiometer of around 100kΩ can be used instead of the 47kΩ resistor. Additionally, the 10µF capacitor value can be modified for further experimentation. While alternately flashing LEDs is an excellent introduction to electronics, the basic on-off circuit can become monotonous. The next section will explore enhancements to create a flashing effect similar to that of a police car, within certain limitations.

The circuit utilizes a 555 timer in astable mode, where it generates a square wave output that alternately activates two LEDs. The frequency of oscillation is primarily determined by the resistor-capacitor (RC) time constant formed by the 2.2kΩ resistor, the 47kΩ resistor, and the 10µF capacitor. The timing interval for the high and low states of the output can be calculated using the formula:

\[
f = \frac{1.44}{(R1 + 2R2) \times C}
\]

where \( R1 \) is the 2.2kΩ resistor, \( R2 \) is the 47kΩ resistor, and \( C \) is the capacitance in farads.

The output from the 555 timer is connected to the anodes of the two LEDs, with the cathodes connected to ground through appropriate current-limiting resistors. This configuration allows one LED to turn on while the other turns off, creating a flashing effect. By substituting the fixed 47kΩ resistor with a potentiometer, users can vary the resistance, thereby adjusting the flashing speed to suit their preferences.

The 10µF capacitor can also be varied to influence the timing characteristics of the circuit. Larger capacitance values will result in longer flashing intervals, while smaller values will increase the frequency of the flashing.

To enhance the visual effect of the flashing LEDs and simulate a police car light pattern, additional circuitry can be introduced. This may involve using additional 555 timers or other timing circuits to create a more complex flashing sequence. The goal is to create a pattern that alternates quickly between the two LEDs, possibly incorporating a third LED for a tri-color effect typical of emergency vehicles.

In conclusion, this simple LED flasher circuit using a 555 timer is an excellent project for beginners, offering opportunities for experimentation and modification to achieve various lighting effects.For a lower parts count than the 2 transistor multivibrators, 2 LEDs can be alternately flashed with a 555 integrated circuit configured as shown in Schematic 2. I chose the combination of a 2K2 and a 47K resistor to determine the oscillation frequency along with the 10 uF capacitor connected to pins 2 and 6.

You can practically change the (R Spee d) 47K value to between 10K and 100K or more. Greater resistance = lower speed. You may also wish to connect up a 100K or so potentiometer instead of the 47K resistor for a variable speed version. Additionally, the 10 uF capacitor value can be changed. Feel free to experiment. Although, alternately flashing LEDs is great for the beginner to electronics, the basic one ON, one OFF circuit gets boring quickly.

In the next section, we will try to improve the look and try to approximate a flash like a police car (within limits). 🔗 External reference