Forget fiddling with voltage knobs, this clever circuit uses a 555 chip and a technique called PWM Pulse Width Modulation to control your DC motors speed.
By rapidly switching the motors power on and off in short bursts we can effectively adjust the average voltage, it experiences ultimately controlling its speed.
It is like a dimmer switch for your motor.
Circuit Working:
Parts List:
| Category | Description | Quantity | Wattage |
|---|---|---|---|
| Resistors | 470Ω, 1k | 1 each | 1/4 watt |
| Potentiometer | 5k | 1 | |
| Capacitors | Ceramic 1nF, 100nF | 1 each | |
| Semiconductors | IC 555 | 1 | |
| Transistor BD679 | 1 | ||
| Diodes | Diode 1N4004 | 1 | |
| Diode 1N4148 | 2 | ||
| Other | 6V Motor | 1 |
Circuit working is carried out below:
In this circuit, the 555 IC integrated circuit is set up as an astable multivibrator.
In other words, it produces an output signal that is a continuous square wave.
The timing components R1, C1 and the variable resistor P1 determine the frequency of the output signal.
Adjusting P1 also modifies the resistance value, which modifies C1s charge and discharge timings and finally the frequency of the output square wave.
A transistor BD679 that serves as a switch is fed the square wave output of the 555 IC.
The square wave signal quickly turns on and off the transistor enabling pulsing current to flow to the motor.
The duty cycle is defined as the ratio of the pulses on to off times.
The duty cycle of the pulsing current to the motor may be successfully adjusted by altering the frequency of the output signal generated by the IC 555 .
The duty cycle of the pulsing current determines the average voltage that the motor experiences.
The motor spins faster when the duty cycle is higher i.e longer on time.
This is because a higher average voltage is produced.
On the other hand a reduced average voltage and a slower motor speed are the outcomes of a reduced duty cycle i.e shorter on time.
There is a speed control knob on P1, by varying P1 you may regulate the average voltage to the motor and its speed by altering the duty cycle of the 555 IC output signal.
When the transistor turns off the 1N4148 diode D2 guards against voltage spikes that might harm the 555 timer integrated circuit.
The circuit is shielded from back electromagnetic field EMF produced by the rotating motor by the 1N4004 diode D1.
Formulas:
You may use the following formula to create an astable multivibrator circuit for a motor PWM (Pulse Width Modulation) speed controller by utilizing the IC 555:
Formula for Frequency (f):
The following formula may be used to get the oscillation frequency in an astable multivibrator circuit that uses a 555 IC:
f = 1.44 / (R1+2*R2)*C
where,
- The resistors attached to the 555 IC are R1 and R2.
- The timing capacitor attached to the 555 IC is represented by C.
Duty Cycle Formula:
The output waveforms duty cycle D, which establishes the pulse width and, therefore the motor speed is provided by:
D = R2 / R1+2 * R2
The duty cycle may be changed by adjusting R2 (the 1k resistor in this case) or by substituting a potentiometer for the fixed resistor in R2, which enables PWM based variable speed control of the motor.
How to Build:
To build a Simple Motor PWM Speed Controller Circuit using IC 555 follow the below mentioned steps for proper connections:
- Gather all the components mentioned in the diagram.
- Connect pin 1 of IC 555 to ground.
- Connect pin 2 to pin 6 of IC 555.
- Connect pin 3 of IC 555 to base of transistor T1 through resistor R1.
- Connect pin 4 of IC 555 to positive supply of 6V.
- Connect pin 5 of IC 555 to ground through capacitor C2.
- Connect capacitor C2 to ground through pin 2 of IC 555.
- Connect pin 6 of IC 555 to one leg of P1 potentiometer.
- Connect pin 7 of IC 555 to one end of both diodes D2 and D3 and other end of diodes connect to rest 2 legs of P1 pot.
- Connect pin 8 of IC 555 to positive supply of 6V.
- Connect one end of resistor R2 from pin 7 of IC 555 and other end to positive supply.
- Connect transistor T1 Emitter to ground, collector of transistor T1 to one end of 6V motor, base to pin 3 of IC 555 through resistor R1.
- Connect one end of diode D1 to collector of transistor T1 and other end between 6V motor and positive supply.
- Connect 6V motors one end to collector of transistor T1 and other end connect to positive supply.
Additional Notes:
- The motor speed controller circuits operational range is determined by the values of the capacitor and resistors.
- Depending on the particular motor you are using, these numbers might need to be changed.
- Verify that the transistor you select is capable of handling the motors current rating.
- The circuit must have a flyback diode D1 to be shielded from back EMF.
Conclusion:
To conclude, a basic and affordable method of regulating the speed of a DC motor is provided by a PWM motor speed controller circuit based on a IC 555 .
Through the use of a 555 IC and a transistor to modify the duty cycle of a pulsing current, you can successfully change the average voltage that the motor experiences which in turn controls its speed.
References:
NE555 Based Speed Controller circuit – Contradicting Pins in 2 Tutorials