Pin Diagram, Specifications & Features

The 555 timer is an integral part of electronics projects. Whether it’s a simple project involving a single 8-bit microcontroller and a few peripherals or a complex project involving System on Chips (SoCs), a 555 timer is involved. These provide time delays, as an oscillator and as a flip-flop component among other applications.

The 555 was introduced in 1971 by the American company Signetics, and the 555 is still widely used due to its low price, ease of use, and stability. It is made by several companies in the original bipolar and low power CMOS types. According to an estimate, 1 billion units were manufactured in 2003 alone.

Depending on the manufacturer, the standard 555 timer package includes 25 transistors, 2 diodes, and 15 resistors on a silicon chip mounted in a small 8-pin dual-line package (DIP-8). Variants consist of combining several chips on one board. However, 555 is still the most popular. Let’s look at the pin diagram to get an idea of ​​the integrated timer (IC) before we talk about the workings of the 555 timer.

555 Timer IC: Block Diagram
555 timer working: pin configuration
8-pin DIP . configuration

Diagram and description

pin Noun Goal
1 GND Ground reference voltage, low level (0V)
2 trigonometry

The output pin rises and the interval starts when that input drops below 1/2 the CTRL voltage (which is usually 1/3 FifthCopy, CTRL is 2/3 FifthCopy by default if you leave CTRL open). In other words, OUT is high as long as the trigger is low. The timer output depends entirely on the amplitude of the external trigger voltage applied to this pin.

3 Outside This output is pushed to approximately 1.7 volts below +FifthCopy, or to GND.
4 Reset

The time interval can be reset by pointing this input to GND, but the timing does not start again until the RESET rises above approximately 0.7V. TRIG that exceeds the threshold.

5 control

Provides “control” access to the internal voltage divider (default, 2/3 FifthCopy).


The timing interval ends (high out) when the voltage at the threshold is greater than that at CTRL (2/3 .). FifthCopy if CTRL is open).

7 dis

open mosque Output that may discharge a capacitor between periods. In phase with output.

8 FifthCopy

Positive supply voltage, which is usually 3 to 15 volts depending on the variance.

Some important features of the 555 timer:

The 555 timer is used in almost every electronic circuit today. For a 555 timer that acts as a flip or a multivibrator, it has a certain set of configurations. Some of the key features of the 555 timer will be,

  • It operates from a wide range of power from +5V to +18V.
  • Sink or get 200 mA of load current.
  • External components must be chosen correctly so that timing periods can be made into several minutes with frequencies in excess of several hundred kilohertz.
  • The output pin of the 555 timer can drive a transistor-transistor logic (TTL) due to its high output current.
  • It has a constant temperature of 50 parts per million (ppm) per degree Celsius change in temperature which is equivalent to 0.005%/degree Celsius.
  • The duty cycle of the timer is adjustable.
  • Also, the maximum power dissipation per pack is 600 mW, and the trigger pulse and reset inputs are logical compatibility.

555 working time

The 555 generally operates in 3 modes:

  1. stable
  2. monostable
  3. bistable modes.

stable mode

This means that there will be no constant level of output. So the output will fluctuate between high and low. This property of unstable output is used as clock or square wave output for many applications.

monostable mode

This configuration consists of one stable and one unstable state. Steady state either high or low can be selected by the user. If the constant output is set to high (1), the timer output is high (1). When the interrupt is applied, the timer output drops (0). Since the low state is unstable, it switches to high (1) automatically after the interrupt has passed. This is the case for low mono static mode.

Dual Stabilization Mode

In bistable mode, both output states are stable. In each interrupt, the output changes from low (0) to high (1) and vice versa, and remains there. For example, if we have a high output (1), it will go low (0) as soon as it receives an interrupt and stay low (0) until the next interrupt changes state.

This datasheet should provide an insight into the details: 555 Timer IC

The video below from Skinny R&D offers insight into the 555 timer as well.

Also let us know if Jason has indicated that the 555 timer works as you wish.

More tutorials are available in the Learning Corner.

This article was first published on June 4, 2017 and was most recently updated on January 19, 2022.

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