PIC + PWM

PIC + PWM

hey guys, nice to see you again and i hope you are enjoying reading my articles .

today topic is how to use PWM with microcontroller. we ll use PIC16F877A as our microcontroller, we ll discover what's PWM? how it works? and for what we need it?

PWM

A pulse width modulated (PWM) signal is a method of generating an analog signal using a digital source. A PWM signal consists of two main components that define its behavior: a duty cycle and a frequency. The duty cycle describes how long the signal is in the high (active) state as a percentage of the duration of a complete cycle. The frequency determines the speed at which the PWM cycles (for example, 1000 Hz would be 1000 cycles per second) and therefore how fast it goes from high to low and vice versa. By changing the state of a digital signal fast enough, and with a certain duty cycle, the output will appear to behave as a constant voltage analog signal when it powers devices.

How it works

Example: To create a 3V signal, given a digital source that can be high (active) at 5V or low (inactive) at 0V, you can use the PWM with a duty cycle of 60% to return 5V 60 % time. If the cycles of the digital signal are sufficiently short, the visible voltage on the output appears to be the average voltage. If the low voltage of the digital signal is 0 V (usually the case), the average voltage can be calculated by multiplying the high voltage of the digital signal by the duty cycle, ie 5 V x 0.6 = 3 V. A duty cycle of 80% would produce 4V, a 20%, 1V, and so on.

when using PIC the generation of PWM signal needs  the module CCP (capture compare pwm) which uses generally TIMER2 of our PIC.

since the TIMER2 is on 8 bits, period resolution is 256 wich mean that high level(5v) is defined by 255 and low level (0v) is defined by 0.

Uses of PWM

PWM signals are used in a wide range of control applications. They are mainly used to control DC motors but can also be used to control valves, pumps, hydraulic systems and other mechanical parts. The frequency required for the PWM signal depends on the application and the response time of the powered system. Here are some applications and the minimum frequencies typically required for the PWM signal:

- Heating elements or systems with long response time: 10 to 100 Hz, or more.

- DC electric motors: 5 to 10 kHz or more.

- Power supplies or audio amplifiers: 20 to 200 kHz, or more.


example of PWM using PIC16F877A

for this example we ll need :
- PIC16F877A
- Crystal 20MHz
- Capacitor 15pF
- Lamp
- Switch

Download code :

click here

Simulation