555 Pulse Generator circuit

This is a pulse generator circuits or standard Astable Multivibrator oscillator or free running circuit using IC555 timer,NE555,LM555 . We use it for digital Logic circuits. IC-555 is popular easy to use small size with 8 pins. It is combining  analog and digital chip. Basic using it need the voltage supply 5V to 15V, Maximum supply voltage 16v – 18v, Current consumption  about 10mA, Maximum Output Current is 200mA. Maximum  frequency  output is 500kHz.

There are many ways to use the IC555.  We can use  them in three different types of oscillators:
(1)Astable Multivibrator oscillator
If frequencies  more than 1 cycle per second, it is an oscillator (pulse generator or square wave oscillator).
But frequencies lower than 1 cycle per second it is TIME DELAY.
(2) Monostable (ONE SHOT) changes state only once per trigger pulse
(3) Voltage Controlled Oscillator (VCO)

Now we will learn about pulse generator with IC-555 below basic circuit.

Simple Pulse Generator circuit by IC-555

simple pulse generator circuit using IC-555

In the circuit above. First of all the current from the power supply flow to the capacitor-C1 charges via the Resistor-R1 and R2, then the voltage in the capacitor reaches 2/3 of the supply voltage, pin 6 detects  this voltage, cause pin 7 cut off this voltage to Ground(0v).
Thus the capacitor-C1 discharges through the resistor-R2 until its voltage is 1/3 of the supply and pin 2 detects this voltage and pin 7 not connect (turns off).  The C1 will charge and voltage across it grow up  again to repeat the cycle.

The top resistor prevent pin 7  may damage as it shorts to 0v when pin 6 detects 2/3 supply voltage.
Its resistance is smaller than R2 and does not come into the timing of the oscillator.

The output frequency will be approximately 1kHz and the duty cycle 50-50,
The Frequency output (F) = 1/{(R1+2R2)*C1}.

The values units in the formula in ohms, farads, seconds and hertz. This formula is much simpler than that of the previous circuit.

Suppose R1 = 1k, R2 = 10k and C = 0.1uF  The result is approx 900Hz

Parts you will need
R1___________100K 1/4W Resistors tolerance: 5%
VR1__________1M Potmeter
C1,C2________0.01uF 50V Ceramic Capacitors
IC1__________NE555 Timer

We use simple 555 pulse generator idea to builds many circuits for example below

High Power Pulse Generator using LM350T and NE555

Pulse Generator by IC LM350T and 555

The danger beep circuit using IC-555
The danger beep circuit using IC-555

Tone Burst Generator using LM555

Tone Burst Generator using LM555

Annoying high pitch noise generator using IC-555

Annoying high pitch noise generator using IC-555

  1. Audio generator is controlled by light
  2. Tapping morse code circuit
  3. 555 timer audio alarm circuits


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