Friday, 15 July 2016

Light Dimming / DC motor speed control using 555

What is PWM actually?
It's simply controlling the width of the high and low pulses to do something useful. It may be encoding a massage or controlling average voltage.

according to wikipedia 

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique used to encode a message into a pulsing signal.

Voltage Control Application 
Here I have made a simple pulse width modulator using 555 timer.

Here is the circuit Diagram

You can also place a LED in the place of DC motor to control it's brightness.

How the circuit works?

The reset pin is connected to +V, so it has no effect on the circuit's operation.
When the circuit powers up, the trigger pin is LOW as capacitor C1 is discharged. This begins the oscillator cycle, causing the output to go HIGH.
When the output goes HIGH, capacitor C1 begins to charge through the right side of R1 and diode D2. When the voltage on C1 reaches 2/3 of +V, the threshold (pin 6) is activated, which in turn causes the output (pin 3), and discharge (pin 7) to go LOW.
When the output (pin 3) goes LOW, capacitor C1 starts to discharge through the left side of R1 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and discharge (pin 7) pins go HIGH, and the cycle repeats.
Pin 5 is not used for an external voltage input, so it is bypassed to ground with an 0.01uF capacitor.
Note the configuration of R1, D1, and D2. Capacitor C1 charges through one side of R1 and discharges through the other side. The sum of the charge and discharge resistance is always the same, therefore the wavelength of the output signal is constant. Only the duty cycle varies with R1.
The overall frequency of the PWM signal in this circuit is determined by the values of R1 and C1. In the schematic above, this has been set to 144 Hz.
To compute the component values for other frequencies, use the formula:

Frequency = 1.44 / (R1 * C1)
Here is my prototype

Here is a demo video of my prototype