Introduction to Microcontrollers Lab Manual - Microchip

7.1 OBJECTIVE
7.2 PRE-LAB
Lab 7. Pulse-Width Modulator (PWM)
LABS
Configure one of the PIC24FJ256GB110 Output Compare Blocks as a PWM to drive
an LED and generate a “heart beat” similar to the power LED on a Macintosh computer.
7.2.1 Reference Material
• PIC24FJ256GB110 Family Data Sheet (DS39897)
• 16-Bit MCU and DSC Programmer's Reference Manual (DS70157)
• MPLAB IDE User's Guide (DS51519)
• PIC24F Family Reference Manual – Section 8. Interrupts (DS39707)
• PIC24F Family Reference Manual – Section 12. I/O Ports with Peripheral Pin
Select (PPS) (DS39711)
• PIC24F Family Reference Manual – Section 35. Output Compare with Dedicated
Timer (DS39723)
7.2.2 Pulse-Width Modulation (PWM) Mode
Pulse-Width Modulation is used to efficiently regulate the amount of electrical power
delivered to a load by quickly switching power between fully ON and fully OFF.
The “duty cycle” is the proportion of ON time in the “period” and is often expressed in
percentage. 75% duty cycle would be delivering power ¾ of the time, and 100% would
be fully on.
A very simple implementation can be used to deliver an average voltage of 1.67V by
pulse-width modulating 5V with a 33% duty cycle as illustrated below.
FIGURE 7-1: BASIC PWM TO CONTROL POWER DELIVERY
A more complicated implementation can be used to deliver sinusoidal power. This is a
similar example to what we will be doing in this lab.
2011 Microchip Technology Inc. DS51963A-page 51