Section 5. Design Considerations; Introduction; Grounding; Infrared And Visible Led Drive Circuit - Freescale Semiconductor M68HC08 Reference Manual

Using the asb520 mc68hc908qt2 based infrared remote control reference pc board designer reference manual

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Designer reference manual (124 pages)

Table Of Contents

Table of Contents

Designer Reference Manual — DRM045

5.1 Introduction

5.2 Grounding

5.3 Infrared and Visible LED Drive Circuit

Using the ASB520 MC68HC908QT2 Based Infrared Remote Control Reference PC Board

MOTOROLA

Freescale Semiconductor, Inc.

Microcontroller systems, in general, have a number of important design

considerations related to PC board layout and grounding considerations.

These design considerations are discussed in

and Visible LED Drive

of the reference board's major circuits are included in

LED Drive Circuit

and

PC board layout is an important design consideration. In particular, ground

planes and how grounds are tied together influence noise immunity. To

maximize oscillator noise immunity, it is a good practice have ground plane

under the resonator, X1. One good grounding practice is to carry all of the

ground connections, in a star configuration, to a single point which could be the

power supply's bulk capacitor or in this case, the battery ground terminal.

Figure 5-1

is the driver schematic, used to drive both LEDs on the PC board.

Because the microcontroller will not source or sink enough current to drive the

two LEDs, a discrete driver is necessary. This circuit uses two transistors. The

first transistor is a small signal NPN, followed by a small signal PNP transistor.

JP4

To PTA0

IR_DISC

Figure 5-1. Infrared LED Drive Circuit

Design Considerations

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