With the help of circuit diagram explain the working of 555 timer. Also discuss its applications.

Q.) With the help of circuit diagram explain the working of 555 timer. Also discuss its applications.

 Subject: electronic devices and circuits

Working of the 555 Timer

The 555 timer IC is a versatile and widely used integrated circuit that can be used in a variety of timing and pulse generation applications. It can be configured in either astable, monostable, or bistable modes. Here, we will focus on the astable mode, which allows the 555 timer to function as an oscillator.

Circuit Diagram

Below is a basic circuit diagram of a 555 timer configured in astable mode:

      +Vcc
       |
       |
      .-.
      | | R1
      | |
      '-'
       |
       +--------2
       |        |
       |      +---+
       |      |   |
       |      |7  |
       |      |   |
       |      +---+
       |        |
       |        |
      .-.       |
      | | R2    |
      | |       |
      '-'
       |
       +--------6
       |        |
       |      +---+
       |      |   |
       |      |6  |
       |      |   |
       |      +---+
       |        |
       |        |
       |        |
      === C1    ===
      GND      GND

Step by Step Working

  1. Power Supply: The 555 timer requires a power supply, which is connected to pin 8 (Vcc) and pin 1 (GND).

  2. Threshold and Trigger Pins: Pins 6 and 2 are the threshold and trigger pins, respectively. They are connected together in astable mode, which allows the timer to self-trigger and operate as an oscillator.

  3. Discharge Pin: Pin 7 is the discharge pin, which is connected to ground through resistor R2.

  4. Output Pin: Pin 3 is the output pin, where the oscillating signal can be taken from.

  5. Control Voltage Pin: Pin 5 is the control voltage pin, which can be used to modulate the timing externally. It is often left unconnected or connected to a capacitor to ground to prevent noise affecting the timing.

  6. Reset Pin: Pin 4 is the reset pin, which can be used to reset the timing cycle. It is usually connected to Vcc to prevent accidental resets.

Operation in Astable Mode

  1. Initial Condition: When the circuit is first powered, the capacitor C1 is uncharged, and the output of the 555 timer is high.

  2. Charging Phase: The capacitor C1 starts charging through resistors R1 and R2. The voltage across C1 increases until it reaches 2/3 of Vcc.

  3. Threshold Action: Once the voltage across C1 hits 2/3 Vcc, the threshold comparator inside the 555 timer triggers, flipping the internal flip-flop and causing the output to go low. The discharge pin (pin 7) is also connected to ground, allowing C1 to discharge.

  4. Discharging Phase: The capacitor C1 discharges through resistor R2 until the voltage across it falls to 1/3 of Vcc.

  5. Trigger Action: When the voltage across C1 drops to 1/3 Vcc, the trigger comparator activates, resetting the internal flip-flop, which causes the output to go high again, and pin 7 is disconnected from ground, allowing C1 to start charging again.

  6. Cycle Repeat: This charging and discharging cycle repeats indefinitely, creating a square wave output at pin 3.

Frequency Calculation

The frequency of the oscillation in astable mode can be calculated using the following formula:

[ f = \frac{1.44}{(R1 + 2R2) \times C1} ]

Duty Cycle Calculation

The duty cycle of the waveform can be calculated using the following formula:

[ Duty\ Cycle = \frac{R1 + R2}{R1 + 2R2} \times 100\% ]

Applications of the 555 Timer

The 555 timer is used in various applications due to its versatility. Here are some common applications:

Application Description
Pulse Generation Generates pulses for digital circuits, servos, and other devices.
Frequency Division Divides the frequency of a signal by a certain factor.
Time Delay Provides a time delay before turning on a device.
Pulse Width Modulation Controls the power supplied to devices such as motors by varying the pulse width.
Tone Generation Generates audio tones for alarms, doorbells, and other signaling devices.
Light Dimming Controls the brightness of lights by adjusting the duty cycle of the power signal.
Speed Control Regulates the speed of motors by adjusting the frequency or duty cycle of the control signal.

The 555 timer's simplicity, low cost, and stability make it suitable for a wide range of applications in both hobbyist projects and commercial products.