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Showing posts from November, 2009

Experiment No. 8: Use of PWM to control the brightness of a LED.

Introduction:
A PIC16F628A has an in-built Capture/Compare/PWM (CCP) module for which the I/O pin is served by RB.3 (Pin No. 9). In this experiment we are going to use the CCP as a PWM to control the power to a LED. PWM stands for the Pulse Width Modulation where the width of a digital waveform is varied to control the power delivered to a load. The underlying principle in the whole process is that the average power delivered is directly proportional to the modulation duty cycle. The term duty cycle describes the proportion of on time to the regular interval or period of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on.
Image Source: http://www.micromouseinfo.com/introduction/images/intro_hardware/PWMod.gif The mikroC has an in-built library functions for PWM hardware module. Click here for details.

Experiment No. 7: Timers and Interrupts

Background
Many microcontroller applications like generating periodic signals, measuring time interval, keeping date and time, use time as their variable. Therefore, microcontrollers need to have some internal resources to accurately measure time. The PIC16F628A has 3 timer modules which are known as Timer0, Timer1, and Timer2. The basic unit of a timer is a free-run 8-bit or 16-bit incrementing synchronous counter which can be programmed to count internal or external pulses. The count number stored by each counter can be read or modified by accessing the special function register associated with that timer. Some of the bits in these registers are also the indicators of timer overflow, which, therefore, can generate interrupt request to the microcontroller. The use of timer modules to keep record of time elapsed allows the microcontroller to carry on with its other operations like controlling outputs, reading inputs, etc.

Timers can also have another asynchronour counter, known as pr…