Weight Measurement System - Microprocessor Based Systems - Lecture Slides, Slides of Microprocessor and Interfacing

The important point in the lecture slides of the Microprocessor Based Systems are:Weight Measurement System, System Application Example, Point of Sale, Involves, Load Cells, Signal Conditioning, Application Program, Statement of the Problem, Checkout Process, Similar

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2012/2013

Uploaded on 05/07/2013

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Lecture 16
Complete System Example
A Weight Measurement System
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Lecture 16

Complete System Example

A Weight Measurement System

Lecture Overview

  • System application example
    • A point of sale weight measurement system
    • Involves
      • Load cells and signal conditioning
      • Application program
  • REF: Chapter 14
  • Many chapters plus the 68HC11 reference manual.

Some background

  • Load cells are transducers that covert applied force, such as weight, into a differential electrical output voltage signal.
  • Load cells – foil type strain gauges
    • Use a Wheatstone bridge circuit to output a signal that can be input to the microcontroller A/D.
    • Foil type strain gauges measure the deflection of the sensing beam to which they are attached. The beam deflects when a load is applied and thus the ability to measure weight is achieved.

The Load Cell setup

  • The basic setup to measure weight using a strain guage.

Load Cell Specification

  • Parameters to specify
    • Excitation voltage – typically a maximum
    • Terminal resistance input – used to determine power consumption – manufacturers specify minimum resistance.
    • Rated capacity – in pounds of kilograms
    • Rated output – in mV/V – specifies the output signal per pound given an input voltage of V

Interface to the microcontroller

  • Practical load cell circuit –
  • Ready for input to conditioning

Fig continued.

  • The full setup for interfacing

If the signal is noisy

The enter subroutine

  • Again have modules to break down

The measure subroutine

  • Note level of action in each box.
  • What type of code is this?

Lecture summary

  • In this lecture we have looked at a system implementation where a microcontroller would be used.
  • System in an integration of both hardware and software design and implementation.
  • The software for the system is 8 ½ pages in chapter.
  • Note the documentation within the software code!!!

Assignment

 None