555 Timer Pinout Details

555 Timer Introduction:

If you have an idea to do some kind of electronics projects like time delay circuits, projects involving oscillator, multivibrators, then you should know about the 555 timer IC completely.

In this post we see the 555 timer pinout details. Before proceeding further we will see some of the facts about this IC.

  1. The 555 timer is an 8-pin IC which is one of the most popular electronic devices used in industrial electronic circuits.
  2. The reason of this IC's popularity is its tremendous versatility. 
  3. The supply voltage for the IC is from 3V to 16V.
  4. The 555 timer IC is used in time delay circuits.
  5. It is also used in an oscillator circuits.

555 Timer Pins Identification:

  • The 555 timer IC has a notch at one end. In some packages a dot will be available on one of the pin.
  • That notch or the dot is used to identify the pin#1.
  • Once the pin#1 is identified, the other pins are numbered as shown in above figure.  

555 Timer Pinout Details:
Following is an explanation of each pin and its function.

Pin-1 : Ground
This pin is connected to the circuit ground.

Pin-2: Trigger

  • To trigger the unit, this pin must be connected to a voltage that is less than 1/3 VCC.
  • VCC =  Supply voltage to the 555 timer IC = From 3V to 16V.
  • This condition will be achieved by connecting pin-2 to circuit ground.
  • The connection to ground( ie, 1/3VCC) must be momentary.
  • If the pin-2 is not removed from ground, the unit will not operate.

Pin-3: Output
The output turns on when pin-2 is triggered and turns off when the discharge ( pin-7) is turned on.

Pin-4: Reset
When the reset pin is connected to supply voltage( VCC), it allows the IC to operate.
When this pin is connected to ground, it activates the discharge and keeps off the timer from operating.

Pin-5: Control Voltage

  • If the control pin is connected to supply voltage (VCC) through a variable resistor, the ON time of the timer IC is longer. But the OFF time is not affected.
  • If this pin is connected to ground through a variable resistor, the ON time is shorter and the OFF time will not be affected.
  • If this pin is not to be used in the circuit, it is usually taken to ground through a small capacitor.

Pin-6: Threshold
When the voltage across the capacitor connected to this pin becomes 2/3 times the value of supply voltage (VCC), the discharge turns on and the output turns off.

Pin-7: Discharge
When the Threshold pin(pin-6) turns the discharge on, it discharges the capacitor connected to pin -6. The discharge remains turned on until pin-2 retriggers the timer. The discharge then turns OFF and the capacitor connected to pin-6 begins charging again.

Now it is good to understand the internal operation of the 555 timer IC.
How the 555 Timer IC Operates Internally?

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