How to Build a Large-Button Calculator App for Easy Use

Develop a user-friendly calculator app featuring oversized buttons and simplified functions, designed for accessibility and ease of use across various demographics, particularly seniors and those with visual or motor impairments.

Product Requirements Document (PRD)

Goals

Create a calculator app with large, easy-to-read buttons
Implement basic arithmetic functions with a simplified interface
Ensure high accessibility and usability for users with varying abilities
Provide a clean, uncluttered design for ease of navigation

Target Audience

Seniors
Users with visual impairments
Individuals with limited fine motor skills
Anyone preferring a simplified, easy-to-use calculator interface

Key Features

Large, high-contrast buttons for easy visibility and tapping
Basic arithmetic functions (addition, subtraction, multiplication, division)
Clear, legible font for numbers and symbols
Simple layout with essential functions only
High color contrast for better readability
Optional voice feedback for button presses and results

User Stories

As a senior user, I want to easily read and press calculator buttons so that I can perform calculations without straining my eyes or fingers.
As a user with visual impairments, I want high contrast and large numbers so that I can accurately input and read calculations.
As someone with limited dexterity, I want widely-spaced, large buttons so that I can avoid pressing the wrong keys accidentally.
As a casual user, I want a simple interface with only essential functions so that I can quickly perform basic calculations without confusion.

Technical Specifications

Recommended Stack

Framework: React Native (for cross-platform development)
UI Library: React Native Elements (for customizable, accessible components)
State Management: React Context API (for simple state management)
Accessibility: React Native Accessibility API
Testing: Jest and React Native Testing Library

Core Technical Decisions

Use React Native for cross-platform compatibility and code reusability.
Implement custom button components with large touch areas and high contrast.
Utilize React Native's Accessibility API to ensure screen reader compatibility and enhanced usability.
Employ a simple state management solution using React Context for calculator logic.
Implement responsive design to ensure proper scaling on various device sizes.
Use vector icons for crisp rendering at any size.
Incorporate haptic feedback for button presses (where supported).
Implement optional text-to-speech for result readout.

File Structure

/src
  /components
    Button.js           # Custom large button component
    Display.js          # Calculator display component
    Keypad.js           # Grid layout for calculator buttons
  /contexts
    CalculatorContext.js # State management for calculator
  /screens
    MainScreen.js       # Main calculator screen
  /utils
    calculations.js     # Logic for arithmetic operations
    accessibility.js    # Helper functions for accessibility features
  /styles
    theme.js            # Global styles and theming
  App.js                # Root component
/assets
  /fonts                # Custom fonts for better readability
  /icons                # Vector icons for buttons
/tests
  Button.test.js
  calculations.test.js
  MainScreen.test.js
/docs
  accessibility.md      # Documentation on accessibility features
  user-guide.md         # Simple user guide for the app

This file structure organizes the app into logical components, separates business logic from UI, and includes necessary assets and documentation for an accessible, large-button calculator app.