555 timer

555 timer theory
555 timer theory

Have you heard of the 555 timer but don’t know how to utilize it? No worries! The 555’s basic magic and how to use it for electronics projects are going to be revealed. You’ll learn 555 timer basics in minutes. To show how this inexpensive and easy-to-use integrated circuit may bring your prototypes to life, we’ll examine practical 555 circuits using schematics and examples. From astable multivibrators to monostable ‘one shots’, we’ll cover the essential operating modes. With the 555 timer, hobbyists, DIYers, students, and makers can create pulses, time events, and incorporate timing functions. Let’s begin!

What Is a 555 Timer IC?

The 555 timers IC is a popular electrical circuit integrated circuit. This tiny 8-pin chip makes clocks, oscillators, and flip-flops.

A circuit with three 5 kilo-ohm resistors is called the 555 timer. Signetics’ Hans Camenzind designed it in 1970. Philips Semiconductors later bought it. This versatile IC chip has been used in thousands of circuits and applications.

Key features of the 555 timer include:

  • It might be monostable or astable multivibrator.
  • It can be triggered and reset on demand, and function as an oscillator or timer.
  • It outputs much current.
  • It works with 4.5–18V power supply.

How 555 Timer Works

The 555 timer has 25 transistors, 2 diodes, and 16 resistors on a small silicon chip. Two comparators monitor capacitor voltage and control output. The threshold and trigger inputs govern output pulse timing.

While the 555 timer is astable, the capacitor charges and discharges 1/3 to 2/3 of the supply voltage. The frequency of the oscillation depends on the resistor and capacitor values. In monostable mode, the 555 timer outputs a single pulse in response to a trigger input.

The 555 timer is a great IC for novices to explore with. You can make numerous entertaining circuits and devices with little cost and effort. This ancient chip is still useful for creative electronics projects after decades.

How the 555 Timer Works

An integrated device, 555 timers create clock signals and time delays. The device has three 5 kiloohm resistors, hence its name. The 555 timer monitors capacitor charge and discharge using comparators.

The 555 timer monitors capacitor voltage with two comparators. Threshold comparators detect capacitor voltages at 2/3 of supply voltage. The trigger comparator detects when the capacitor voltage drops to 1/3 of the supply voltage.

When engaged, the 555 timer charges the capacitor via resistor. This raises capacitor voltage. When it hits 2/3 of the supply voltage, the threshold comparator turns the 555 timer output low. The capacitor is discharged using a discharge resistor. As the voltage drops to 1/3 of the supply, the trigger comparator turns the output high and the cycle repeats.

Charge and discharge resistors regulate oscillation timing. Lower resistance speeds charging and discharging, increasing oscillation frequency.
Supply voltage determines oscillation peak voltage. More supply means more peak voltage.
An external reset pin might prematurely deplete the capacitor and resume the timing cycle.
High or low output can be read on the output pin. Trigger additional circuits and devices with this digital output.
The 555 timer is helpful for pulse production, oscillation, and timed events.


Oscillators provide oscillating output voltages. Square wave oscillations from the 555 switch between low and high voltage levels at a constant frequency. You can construct an astable oscillating multivibrator by connecting the charging/discharging pin (6) and threshold pin (2) to a capacitor and resistor. Adjust capacitor and resistor values to alter frequency.

Pulse generators

A pulse generator generates a fixed-duration voltage pulse. In a 555 circuit, connect pin 2 to a resistor and capacitor but not pin 6. A single pulse is generated by voltage on pin 4. RC network values determine pulse width. A single pulse can trigger other circuits.


Simple timer circuits are the 555’s specialty. Monostable mode disconnects pin 6. The timer outputs a voltage pulse on pin 3 for a predetermined duration after pin 2 is powered. Pin 2’s RC network determines duration. This can be used to make delay circuits, pulse stretchers, shrinkers, and missing pulse detectors.

The 555 timer IC lets you build simple circuits and prototypes without much training. After learning the basics, the possibilities are unlimited. You can use the 555 to build a simple oscillator, generate timed pulses, delay, or activate other devices. Change resistor and capacitor values to learn how they affect frequency, pulse width, and timing in these basic 555 circuits.

Tips for Using 555 Timers

The 555 timer IC is versatile and works in many circuits. Tips to maximize 555 timers:

Choose the right 555 timer for your needs

Many 555 timers are available, including the LM555, NE555, TLC555, LMC555, and ICM7555. The most prevalent are LM555 and NE555. Use CMOS timers for minimal power. For high-speed circuits, use LM555 or NE555.

Provide proper power connections

555 timers need 4.5V to 15V DC power. Connect pin 1 to ground and pin 8 to positive. Bypass capacitors between supply and ground reduce noise.

Set the timing with external components

The RC network between pins 6 and 2 controls 555 timers timing. Use higher resistors for longer times and capacitors for shorter times. In most 555 circuits, C ranges from 0.1μF to 10μF and R from 1kΩ to 1MΩ.

Use the output and control pins

Pin 3 outputs high or low voltage depending on timer status. Control Voltage pin 5 controls time externally. Pulling pin 4 low resets the timer.

Test your timer circuits

Always create and test 555 timer circuits on breadboard before soldering to protoboard or PCB. Make sure time periods and outputs work. Change components before finishing the design.

These suggestions will help your 555 timer projects succeed. Have more questions? Let me know!


This is a basic guide to utilizing 555 timers. For beginners, we covered operation theories, setups, and example circuits. With this foundation, you can securely use these flexible chips in electronics applications.. Electronics may seem strange at first, but with some hands-on experimenting, persistence, and coaching, you’ll be inventing and innovating soon. Use your breadboard to explore the world of 555 timers!

Be the first to comment

Leave a Reply

Your email address will not be published.