Analog Weighing Scale Using Load Cell

Abstract

This project presents a weighing scale utilizing a load cell, where a strain gauge load cell is interfaced with an amplifier to measure the weight of objects and display the readings on a screen.

The methodology is centered around four main components:

1. A 10kg load cell was selected and strategically mounted on the enclosure to ensure accurate measurements.
2. Two regulated power supplies (6V and 5V) were designed to provide stable power to the circuit.
3. An amplifier circuit was implemented to increase the low-level signal from the load cell.
4. A microcontroller-based system featuring the ATmega328p processes the data and displays real-time weight readings on a 16x2 LCD screen.

This system offers a cost-effective, reliable, and accurate solution for weight measurements up to a maximum capacity of 100N (10kg).

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Table of Contents

• Overview
• Introduction
• Components
• Circuit Diagram
• PCB Layout
• Working Principle
• Setup and Installation
• Usage

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Overview

This project presents the design and development of an analog weighing scale utilizing a load cell and an opamp-based signal amplification circuit. The objective is to accurately measure weight by converting the analog signal from the load cell into a readable format, which is then processed by a microcontroller.

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Introduction

This project demonstrates the practical implementation of an analog weighing scale using a load cell and an amplification circuit designed with LM324N operational amplifiers. The load cell detects applied force and outputs a low-level electrical signal, which is then amplified for further processing by a microcontroller.

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Components

• Load Cell (10kg)
• LM324N Operational Amplifiers (Opamps)
• Resistors & Capacitors
• Custom-designed PCBs:
  • Amplifier & Microcontroller section
  • Power Supply section
• ATMega328p Microcontroller
• 230V AC to 12V AC Transformer
• Regulated Power Supply (6V and 5V)
• 16x2 LCD Display
• Connecting Wires

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Circuit Diagram

Description

• The load cell outputs a small differential voltage when weight is applied.
• This signal is connected to an instrumentation amplifier circuit.
• The amplified signal is fed into the microcontroller’s ADC (12-bit resolution).
• The power for the system is supplied via a custom-built PCB powered by a step-down transformer.

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PCB Layout

Amplifier and Microcontroller Section

• Schematic and 3D layout for amplification and signal processing.

Power Supply Section

• PCB layout and 3D view of the power conversion circuit (230V AC to 12V AC, then regulated to 6V and 5V).

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Working Principle

1. Load Cell
   When weight is applied, the load cell slightly deforms, altering the resistance of the internal strain gauges.

2. Wheatstone Bridge
   The load cell is wired in a Wheatstone bridge to produce a small differential voltage proportional to the weight.

3. Signal Amplification
   An instrumentation amplifier (based on LM324N opamps) amplifies this voltage for better resolution.

4. Analog-to-Digital Conversion
   The amplified signal is sent to the ADC of the ATMega328p microcontroller for digital reading.

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Setup and Installation

1. Assemble the Circuit
   Refer to the circuit diagram and PCB layouts to connect all components correctly.

2. Power Up
   Connect the AC supply to the transformer, which powers the circuits.

3. Calibration
   Use known weights to calibrate the system for accurate readings.

4. Data Reading
   The output can be observed either on an analog voltmeter or via a digital display connected to the microcontroller.

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Usage

1. Place the Object
   Position the object to be weighed onto the load cell platform.

2. Observe Output
   View the amplified analog signal or digital weight measurement on the LCD or meter.

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