This project implements a real-time DTMF decoder capable of identifying keypad presses from audio signals. DTMF is commonly used in telephone systems where each key press generates two simultaneous tones at specific frequencies.

• Real-time Signal Processing: Continuous audio signal sampling and buffering
• Goertzel Algorithm: Efficient frequency detection without full FFT computation
• DTMF Tone Detection: Supports standard keypad (0-9, *, #) and extended keys (A-D)
• Embedded Systems Ready: LCD display integration and optimised for LPC4088 microcontroller
• EEPROM Storage: Persistent storage for configuration parameters and detected sequences
• Comprehensive Testing: Multiple test implementations and audio samples
• Error Handling: Validates single tone pair detection and handles invalid inputs

• Audio signal buffering and preprocessing
• Quiet region detection for tone separation
• Buffer management for continuous processing

• Goertzel algorithm implementation for frequency detection
• DTMF keymap matching
• Error validation and handling

• LCD display integration for embedded systems
• Real-time result display

1. Signal Acquisition: Continuous sampling of audio input
2. Buffering: Store samples until quiet region detected
3. Frequency Analysis: Apply Goertzel algorithm to detect specific DTMF frequencies
4. Tone Validation: Verify exactly two frequencies (one low, one high) are present
5. Key Mapping: Match frequency pair to corresponding keypad character
6. Output: Display result on LCD

The system utilises EEPROM for persistent storage of:

• Display Mode Configuration: User-selected display mode that persists across power cycles
• User Interface Settings: Toggle between single character and scrolling display modes

• Address 0x00: Display mode setting (0 = single character mode, 1 = scrolling mode)

• Mode 0: Single character display - shows only the most recently detected DTMF character
• Mode 1: Scrolling display - shows a history of detected characters with shifting effect

This DTMF decoder was specifically developed and tested on the LPC4088 microcontroller using the Keil uVision5 IDE.