555 Timer

Introduction 555 Timer

The 555 timer was introduced more than 40 years ago. Thanks to its relative simplicity, its ease of use and its low costs, it has been used in thousands of applications and is still widely used.

555 Timer Characteristics and Pin assignments (DIP 8 pin)

Below Figure shows the pin configuration of 555 timer IC standard dual-line (DIP)  package.

Pin 1 – Ground (GND) this pin is connected to the ground circuit.

Pin 2 – Trigger (TRI) low voltage (less than 1/3 of the supply voltage) applied directly to the input triggers the output of the output (pin 3). The output remains high until the high voltage is applied to the threshold input (pin 6).

Pin 3 – Output (OUT) In a low output state, the voltage is close to 0 V. In a high-state output, the voltage at the supply voltage is below 1.7 V. For example, if the output voltage is 5 V, the output voltage is 3.3 volts. The output can reach 200 mA or plug in (the maximum depends on the supply voltage).

Pin 4 – Reset (RES)

A low voltage (less than 0.7 V) applied to reset the pin has the output (pin 3). This input must be linked to Vcc when it is not in use.

Pin 5 – Pin control (CON)

The threshold voltage (pin 6) can be controlled by a controlled input (set internally at 2/3 of the supply voltage). It can vary from 45% to 90% of the supply voltage. In this way, the length of the output pulse can be changed in the simulation mode or the output frequency in an unstable mode. When it is not in use, it is recommended that this input is connected to the capacitor by a 0.01 uF capacitor.

Pin 6 – Threshold (TRE)

With unstable and injectable methods, the capacitor voltage is synchronized with the portal input. When the voltage in this input exceeds the threshold, the output is up and down.

Pin 7 – Dismissal (DIS)

when the voltage across the capacitor exceeds the threshold. The simultaneous capacitor is released from this input

Pin 8 – supply voltage (VCC)

The connection between the supply voltage is positive.  The time interval of BC in the supply voltage range does not change in the unstable or isolable mode (approximately 0.1%).

Some important features of the 555 timer:

The 555 timer is now used in almost all electronic circuits. For a 555 timer, which acts as an agent or multiple generator, it has a specific set of configurations. Some of the most important functions of the timer are 555:

  • Works with a wide power range from 5 volts to 18 volts.
  • Reduction or delivery of a current load of 200 mA.
  • External components must be selected correctly so that time intervals can be set in minutes with hundreds of kilometers of frequencies.
  • The transistor output of the 555 transistor transistor (TTL) can be controlled due to the high power.
  • Temperature stability of 50 parts per million (ppm) per Celsius phase, equal to 0.005% / ° C.
  • The operating cycle of the timer is adjustable.
  • In addition, the maximum discharge capacity in each container is 600 mW and the release and reset of the inputs are logically exchanged.


The schedule shows that there are 2 comparators, flip-flop, voltage divider, loose transistor and output phase.

The voltage divider has three identical 5k resistors that make up two reference voltages at 1/3 and 2/3 of operating voltage at range 5 to 15V.

Then two comparators will arrive. A comparator is a circuit feature that compares two output input voltages with a positive (reversible) input terminal and a negative (inversion) terminal. If the input voltage on the positive terminal over the input voltage to the negative terminal, the output of the comparator is 1. On the contrary, if the voltage at the negative input terminal exceeds the voltage at the positive terminal, a comparator outputs 0.

A negative input terminal of the first comparator is connected to the voltage divider and “control” at the external terminal with a reference voltage of 2/3, and the positive input terminal connected to the external terminal “Threshold”.

On the other hand, the second terminal is a negative input of the comparator connected to the “Trigger” pin, and the positive input terminal of the voltage divider connected to the reference voltage 1/3.

With three trunks, a portal and a control, we can control the output of the two comparators, which are then fed to an R-S and an input flip-flip. The output of the flip-flop 1 when R 0 and 1 S and, on the contrary, 0 when R 1 and S 0. 0. In addition, the flip-flop reset by PIN “PIN, the external can be rewritten input, so the whole timer can be reset at any time.

In the 555 Timer Package:

Qty. Description Manufacturer P/N
1 Standard Timer Single 8-Pin Plastic Dip Tube NE555P
1 400-Point Solderless Breadboard 3.3″L x 2.1″W WBU-301-R
10 Resistor Carbon Film 10kΩ CF1/4W103JRC
1 9V Alkaline Battery ALK 9V 522
1 9V Battery Snap with 6″ 26AWG Leads BC6-R
2 3-Pin SPDT Slide Switch SS-12E17
2 Radial Capacitor 0.01µF 2.54mm Bulk SS-12E17
1 Radial Capacitor 4.7µF 2.5mm Bulk TAP475K025SCS-VP
10 Resistor Carbon Film 1.0MΩ 1/4 Watt 5% CF1/4W105JRC
10 Resistor Carbon Film 220Ω 1/4 Watt 5% CF1/4W221JRC
10 LED Uni-Color Red 660nm 2-Pin T-1¾ Box UT1871-81-M1-R
100 Resistor Carbon Film 3kΩ 1/4 Watt 5% CF1/4W302JRC
10 Resistor Carbon Film 330kΩ 1/4 Watt 5% CF1/4W334JRC
1 Radial Capacitor 1µF 25 Volt 2.5mm Bulk TAP105K025SCS-VP

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