The 555 timer IC is an integrated circuit that is used in a variety of timer circuits, pulse generators and oscillator applications. The heart of the module is the 555 timer IC that is wired as an astable multivibrator, generating pulses from about 4Hz to 1.3Khz.

This circuit can be used in any project, that requires positive pulses.

To demonstrate the operation, a LED is used at the output of the IC to show the visual indication of the output pulses.

The output frequency of pulses can be adjusted using a potentiometer. The circuit can be operated from any voltage between 5 to 15 volt DC.

## Items Required

For this project we need:

• 1 x 555 Timer IC
• 1 x 10µF Capacitor
• 1 x 1kΩ Resistance and a
• 1 x 10kΩ Potentiometer

## Circuit Diagram

The circuit is very simple.

By connecting pin 2 and 6 we put the 555 timer in astable mode. Astable mode causes the 555 timer to re-trigger itself, producing a stream of pulses [PWM Signals] as long as its hooked up to a power supply.

Pin number 3 is the output pin. By changing the values of R1, R2, and C3 we can change the frequency of output pulses generated at pin number 3.

## How It Works

The working voltage of the circuit is between 5V~15V DC.

As previously discussed 555 timer generates PWM signals when set up in an astable mode by connecting the pin 2 and 6 together.

During each cycle capacitor C3 charges up through both R1 and R2 resistors but discharges itself only through resistor R2 as the other side of R2 is connected to the discharge terminal pin 7.

Changing the values of R1, R2, and C3 will change the frequency of output pulses, or different duty cycle of the square wave coming out of pin 3.

By changing the value of R2 we can change the duration of the OFF cycle.

In this setup the ON time depends on the resistor R1, the left side of the pot and the capacitor C3, while the OFF time depends on the capacitor C3 and the right side of the pot.

Now, lets calculate the output frequency and the duty cycle of the output waveform.

In my setup I have resistance R1 = 1kΩ, R2 = 10kΩ and capacitor C = 10uF

There are many online calculators to calculate this online. I will provide a link to one of the astable calculators in the description below: https://ohmslawcalculator.com/555-astable-calculator

Lets first calculate the value of t1 or the 'capacitor charge “ON” time which is 0.693(R1 + R2 ) * C3. Putting the values together we get 76.23 milliseconds.

Now, for capacitor discharge “OFF” time or t2 we need to multiply 0.693 to R2 and C3, which then gives us a value of 69.3 milliseconds.

Next, the total periodic time T is equal to t1 + t2 which comes out to be 145.53 milliseconds.

The output frequency, ƒ is therefore comes out to be to 6.871Hz.

Which gives a duty cycle value of 52.38%

If you want to have more control over the charging and discharging use a higher value for R2 (100K) and lower value for R1 (1K). That way you will have 99% control over the charging and discharging resistance in the circuit.

The maximum output current of this IC is 200mA therefore to drive a higher current load of up to 1A we have to use a transistor like the BD135.

For driving a much higher current than 1A you can use other high current transistors like TIP31, 2N3055, etc. with a good heatsink. TIP122 can only go up to about 1.5 amps without a heatsink, however it can go up to 5 amps with a good heatsink. IRLB8743 FET is good to around 20 amps without a heatsink.

## The Board

So this is how my board looks like. There are 16 breakout boards in this 100cm  x 100cm assembly. You can download the gerber file from the link below and order it from PCBWay.

## Soldering

Lets start by soldering the IC Base to the board. Then lets solder the potentiometer to the board. After that lets solder the R1 resistor to the board followed by the C3 capacitor to the circuit...