PWM Motor Speed Controller Using 555 Timer

Today’s project is about PWM Motor Speed Controller using just a 555 timer IC. It is useful for varying the speed of a low-powered DC motor. There are many circuits on the web that can control DC motors for electronic project purposes. But when it comes to controlling the motor uniformly and smoothly, the PWM motor speed controller is the best option like using AVR, 8051 and Arduino.

We can also build this motor speed controller using just a variable potentiometer in series with the motor. But for two reasons, we can’t do it for project purposes. Firstly, the variable resistance dissipates excessive energy as heat, so too much power will be wasted. Secondly, we cannot use this method for automation projects.

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What is PWM (Pulse Width Modulation)?

Pulse Width Modulation (PWM) or Pulse Duration Modulation (PDM) is a technique for reducing the average power delivered by an electrical signal. The average value of voltage or current fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. It is basically a square wave in which operates as a switch constantly on and off. It is widely used to control the speed of a DC motor and dimmable light bulb.

How Does PWM Control Motor Speed?

PWM controls the speed by driving the motor with a series of ON/OFF pulses and varying the duty cycle. It depends on the modulator voltage. The higher the voltage, the speed of the motor increases. By keeping the frequency constant, the fraction of time increases when the output voltage is high compared to when it is low.

555 Timer As a PWM Generator

Like microcontrollers, we can also use a 555 timer as a PWM circuit if we design it into astable mode. There is a detailed block diagram and graph of the 555 timers in astable mode. There we can see that the output is “HIGH” when the C1 capacitor is charging through R1 and R2 resistors. While the other part is “LOW” when the C1 capacitor discharge through the R2 resistor.

So we can see that if we change the value of any of the three components, the output value of the whole duty cycle will change. To solve this problem, we need to add a potentiometer instead of just an R2 resistor and add two diodes.

This time “ON Time” will depend on the R1, C1, and the left rotation of the potentiometer while “OFF Time” will depend on only the C1 and right rotation of the potentiometer. Due to the same total resistance during charging and discharging, one cycle of the frequency will also be the same.

Being R1 resistance is so smaller than the potentiometer, the control over the charging and discharging is easy to control. Pin number 5 i.e. control pin of the 555 timer ic is unusable and due to avoid external noise it is connected with a 100nF capacitor. To prevent any output resetting, pin number 4 is used with VCC directly.

The output of the 555 timer ic can only handle 200mA current for load. Due to this reason, we need a MOSFET to drive the motor that exceeds this current rating. I used a MOSFET which is able to handle upto 5A current for this purpose. We need to connect the output with the base of the MOSFET using a 1KΩ resistor. After that, we need a feedback diode parallel to the motor for voltage fluctuations.

Project

Circuit Diagram

Components Required

• 555 Timer IC
• TIP122 MOSFET
• 1N4007 PN Diode
• 100nF Ceramic Capacitor (x2)
• 1KΩ Resistor
• 100KΩ Potentiometer
• Motor
• 9V Battery

Working Principle of PWM Motor Speed Controller

In this project, a DC motor is operated by a simple 555 timer ic. The 555 in this project is being operated in astable mode, which produces continuous HIGH and LOW pulses to rotate the motor.

Surprisingly, we can use this circuit as an astable multivibrator with low costs and materials. In this mode, the 555 timer ic can be used as a pulse width modulator with a few small adjustments to the circuit. The frequency that is needed for operating the motor is provided by the passive elements i.e. resistances and capacitors attached to it.