How can i use pwm to control dc motor ?

[mahm150]

How can i use pwm to control dc motor ?
Any one have tutorial discuss pwm to control dc motor. I already try to do that by avr but i cant observe the difference of speed in the dc motor when change the value of the timers

 

[mister_rf]

Read here:
DC Motor Speed Control using PWM : AVR microcontroller projects
Controlling DC motor with AVR ATtiny13 PWM and ADC Project | ermicroblog
Design with Microcontrollers: Simple PWM DC motor control using MOSFET H-Bridge with AVR ATmega8

 

[ckshivaram]

check this
**broken link removed**
**broken link removed**

 

[Pheetuz]

Have you heard of a H-Bridge circuit? This would allow you to change the direction of rotation of the motor and at the same time if a MOSFET is placed in the ground path of the H-Bridge then you can connect the PWM to the gate of this MOSFET and use it to control the speed of rotation.
Google H-Bridge and see what comes up.

Pete

 

[mahm150]

that's all best but i want to know when the PWM signal generated by controller give the max. speed, min speed and the medium speed

 

[Tahmid]

First you need to understand PWM properly. PWM means that you have a pulse at a specific frequency and the pulse has a duty cycle which determines the time during each pulse that it is high. So, you could have a pulse with frequency 50Hz (just for example). That means that it has a period of 20ms. So, if you have 10% duty cycle, the output pulse is on for 2ms and off for 18ms. If you have 80% duty cycle, the output pulse is on for 16ms and off for 4ms.

You have the minimum motor speed when the duty cycle is 0 or near 0. The maximum motor speed is when the duty cycle is 100% or near 100%. You get "medium" speed (50% speed) when duty cycle is 50%.

Hope this helps.
Tahmid.

 

[mahm150]

how to do that with micro controller like AVR , i do that using fast PWM mode but i am not understand how to make calculation to timer to make the required duty cycle so my DC motor work with speed unknown for me

 

[Tahmid]

Let's say you're using Timer/Counter 2 and Fast PWM Mode. Then, TOP = 0xFF (255). Setting the OCR2 register will set the duty cycle. If you set OCR2 to 128, you get 50% duty cycle. If you set OCR2 to 64, you get 25% duty cycle.

Duty cycle = (OCR2/TOP) * 100%

Study pages 112 and 113 from the datasheet carefully. I've attached just these 2 pages as well.

Hope this helps.
Tahmid.