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AVR401: 8-bit Precision A/D Converter

Features

CC

Introduction

This application note describes how to perform a kind of dual slope A/D conversion

with an AVR microcontroller. The converter is very low cost, requiring only six discrete

components in addition to the AVR. Five of the controller pins are used (see Figure 1).

This example is based on the AT90S1200 device, but any AVR device with a compar-

ator can be used.

Figure 1. A/D Converter

Theory of Operation

The capacitor is charged with a constant current supplied by the transistor. The

capacitor voltage will rise linearly. To discharge the capacitor, the AIN0-pin is set to

output with a “0” applied. A reference voltage at V

work R

reference is turned off, and the voltage level at the AIN1-pin will be the input voltage

V

pin will be V

least 100 times higher than the reference resistors R

ment errors.

V

CC

(AIN0) PB0

(AIN1) PB1

PB7

AT90S1200

PB2

PB3

T

C

R

B

R

in

R

ref 1

R

ref 2

V

in

(V )

ref

8-bit

Microcontroller

Application

Note

Rev. 0953C–AVR–02/03