Dc Motor Speed Control with 8051(89c51,89c52) Microcontroller using PWM Technique and l293d motor driver

This is a simple project/tutorial on how to control Dc motor speed using 8051(89c51,89c52) microcontroller? Dc motor or fan speed is controlled using Pwm(Pulse width Modulation) technique. Their are two ways to generate pulse width modulation signal using 8051(89c51,89c52) microcontrollers. You can generate it by using timers of 8051(89c51,89c52) microcontroller OR you can switch a particular pin (high and low) so rapidly with some arbitrary delay in switching, that a pulse is generated as output on the pin. Best and most easy controlled way to generate PWM signal is by using internal timers of 89c51 microcontroller and in this project i am going to generate PWM using timers of 8051(89c51,89c52) microcontroller.
PWM in simple words changes the output voltage on a specified pin on which it is applied by varying the duty cycle of output wave form. Frequency and duty cycle of PWM signal can easily be varied using timers of 8051 microcontroller. Figure below will clear you about PWM signals and duty cycle. Original signal duty cycle is varyied in the below diagram.

PWM signal

What exactly duty cycle is?

Duty cycle is the time during which the output signal remains high for a period of wave. Period is the total time/length of a single clock wave/cycle. Hence duty cycle is time/length in a single clock cycle during which the output remains high.

Duty Cycle

Motor speed control with 8051 microcontroller – Project requirements

Microcontroller 8051(89c51 or 89c52)
Crystal (11.0592MHz)
Capacitors 2 (33pf)
Push Buttons 9
DC Motor- Fan (Small Toy Motor)
Power Supply (5v)
L293D (DC Motor Driver)

I am generating PWM signal of different duty cycles 00%, 10%, 20%, 50%, 80%, and 90%. 200 us is my base. For 80% duty cycle my time delay is 160 us. PWM for delays greater than 200 us are also generated 500 us, 800 us and 1000 us.

Now how to generate these delays using 8051(89c51,89c52) microcontroller timers? Their are two timers in 89c51 microcontroller Timer-0 and Timer-1. You can use them for delay purposes or for counting an event etc. You can use these timers in Four Modes. I am using them in 16-bit mode. To learn more about timers, their modes and initialization go through the tutorial

8051(89c52,89c51) Microcontrolle Timers

8051(89c52,89c51) are 8-bit microcontrollers. But you can use their timers as 16-bit. To load 16-bit value in timers you use two registers THx and TLx associated with timers. Where THx represents Timer High Byte and TLx represents Timer Low Byte (Note x is 0 or 1 depending on the timer you want to use). Here i am using Timer-0 so I will use TH0 and TL0 registers.

My Duty cycle base is 200 us means at 100 us duty cycle will be 50%. 50% duty cycle means both positive and negative signals are same in length(time). You can see two sine(digital) waves with duty cycles 50% and 75% in the figure at left side. Notice the difference between both waves.

I calculated delay for 00, 20 us, 40 us, 100 us, 160 us, 180 us, 500 us, 800 us and 100 us and loaded the values obtained by the result in TH0 and TL0 registers. Formulas to calculate delay is given below with an example.

You can Calculate values of TH0 and TL0 registers for 00, 20 us, 40 us, 100 us, 160 us, 180 us, 500 us, 800 us and 100 us delays using the formula given on the right side. I calculated the values using the same formula.

PWM is generated on Port-1 pin#0. Pin#0 of Port-1 is connected to L293D. To switch between different duty cycles i used Push Buttons. Each push button corresponds to PWM of different duty cycle. Total 9 push buttons are used in the project. Eight are connected to Port-2 and Ninth one is connected to Port-0 pin#7. Apply 5v at Pin#40&31 of Microcontroller. Ground Pin#20. Connect crystal(11.0592 MHz) to pin#18&19 of microcontroller. Connect capacitors in parallel to crystal.

Delay Calculation for 8051(89c51,89c52) microcontroller.

L293d motor driver with 89c51 microcontroller circuit diagram

Dc Motor Speed Control using 8051(89c51,89c52) microcontroller. L293d interfacing with 89c51 microcontroller.

L293D motor driver

Dc motors needs minimum 5 volts and 80 mA of current to work properly. 8051 microocntroller can not supply this much amount of power as output on its gpio pins. An external driver is needed to accomplish this task. L293d motor driver is best to driver small dc motors so it is made part of our project. L293d connections with 89c51 microcontroller are shown above to learn about L293d working, pin out and configuration go through the below tutorial

L293D Pin out and Working

In the code portion i first included the header file reg51.h. This header file must be included in every project code that is going to be compiled in keil compiler. Some single bits are initialized than. These bits represents push Buttons and Pwm output pin. In the main function first each port is initialized as input or output.
The instruction TMOD=0x01 is initializing Timer-0 in 16-bit Mode. Do not understand take the tutorial.

Timer registers of 89c51 microcontroller

If-else statement is switching between different duty cycles, depending on the push button pressed. In button statements Pwm_B_20=P2^1, 20 represents the duty cycle corresponding to button. Like in statement Pwm_B_60=P2^4, 60 represents the 60 us high time or 30% duty cycle. Delays greater than 200 us means 100% duty cycle.