Morse Code Recognition

A Verilog/FPGA digital design that turns a Digilent Basys3 development board into a real-time Morse code input, decoding, and display device. The system samples a single push-button as a time-varying signal, classifies each press as a dot or a dash, matches the resulting pattern against a Morse code table, and renders the result on the board's LEDs and seven-segment displays.

The project is delivered as two progressively more capable Vivado designs:

	Level 1	Level 2
Input	Single letter per session	Continuous words, up to 4 letters
Output	One decoded letter	Full word across all four 7-segment digits
Extra controls	—	East/West buttons to page through letters, dedicated Letter View switch
Vivado project	Level1/level_1.xpr	Level2/level_2.xpr

Contents

• How it works
• Level 1 — single character decoding
• Level 2 — multi-character word decoding
• Architecture
• Module reference
• Board I/O map
• Getting started
• Repository layout
• License

How it works

Morse code encodes each letter as a sequence of short and long signals — dots and dashes. This project reproduces that encoding using the Basys3's centre pushbutton as the sole input transducer:

1. The user holds the button down for less than 3 seconds to enter a dot, or 3 seconds or more to enter a dash.
2. Each press is timed by a 1 Hz reference ("heartbeat") counter and debounced in hardware before it reaches the decoding logic.
3. After 2 seconds of inactivity following a press, the accumulated dot/dash sequence is compared against a built-in Morse code ROM (A–Z).
4. On a match, the decoded letter is displayed on the seven-segment display; the LEDs track which phase of the input cycle the system is currently in.
5. After 5 seconds of inactivity in the finished state, the system automatically resets and is ready for the next character.

Both levels share this same timing discipline and the same underlying FSM/comparator/ROM pipeline — Level 2 adds a second layer of state to accumulate multiple letters into a word and to browse the result.

Level 1 — single character decoding

• Enter one Morse sequence (up to 4 symbols) using the centre button.
• enableDisp (slide switch) turns the seven-segment display on/off.
• switchDisp toggles between two 7SD view modes:
  • Raw view — shows the dot/dash pattern being entered, symbol by symbol.
  • Letter view — shows the decoded letter once found (or a rolling "Error" indicator while no match exists).
• enableIn (slide switch) gates whether button presses are accepted as input.
• Onboard LEDs (LD0–LD3) indicate the current FSM phase: idle, measuring a press, translating, or ready.

Level 2 — multi-character word decoding

Builds on Level 1's single-letter pipeline and adds:

• Word accumulation — up to 4 decoded letters are packed into a 20-bit word register and displayed across all four digits simultaneously.
• Letter View mode (letterView switch) — freezes the display on one letter/character slot at a time.
• East/West navigation buttons — page left/right through the accumulated letters (and their raw Morse patterns) once in Letter View, via a dedicated spot edge-detector on each button.
• The same dot/dash timing, comparator, and ROM-lookup pipeline from Level 1 is reused per character; only the display/state layer for word assembly is new.

Architecture

Both designs follow the same signal path:

btn_enter ──► debouncer ──► keyProcessor ──► morseCode ──► code_comparator ──► Morse_decoder_rom
                                │                                │                    │
                                ▼                                ▼                    ▼
                              (ready)                         (found/done) ◄──────────┘
                                │                                │
                                └────────────► FSM_letter ◄──────┘
                                                    │
                                                    ▼
                                          sevenSegmentDisp / sevenSegDisp ──► ssdAnode / ssdCathode

• keyProcessor is a 4-state FSM (IDLE → MEASURE → TRANSLATE → READY) that times each button press against the 1 Hz heartbeat, classifies it as a dot (01) or dash (10), and shifts it into a 16-bit symbol buffer (morseCode), 2 bits per symbol, up to 4 symbols per letter.
• code_comparator walks the Morse ROM address space (a small counter-driven sequential search) comparing each entry against the assembled morseCode until it finds a match or exhausts the table (Z at address 28).
• Morse_decoder_rom is a combinational lookup table mapping ROM addresses 3–28 to the dot/dash encoding for A–Z.
• FSM_letter is the top-level control FSM (IDLE → CODE_CHECK → DISP → CLOSE) that sequences the comparator search and drives the letter display / reset lifecycle.
• sevenSegmentDisp (Level 1) / sevenSegDisp (Level 2) time-multiplexes the four 7-segment digits at 1 kHz and selects what to display based on the current mode (raw pattern, decoded letter, or full word).
• debouncer and heartbeat are shared timing primitives: the debouncer samples a button through a 3-stage shift register on a slow clock edge to reject contact bounce, and the heartbeat is a generic clock divider used everywhere a periodic tick is needed (1 Hz timing, 1 kHz display refresh, debounce sampling).
• spot (Level 2 only) is a one-shot rising-edge detector used to turn the debounced East/West signals into single pulses for letter navigation.

Module reference

Module	Levels	Purpose
Morse_decoder_TOP	1, 2	Top-level design; wires all submodules to board I/O.
keyProcessor	1, 2	Times button presses, classifies dot/dash, assembles the symbol sequence.
code_comparator	1, 2	Sequentially searches the ROM for a matching Morse pattern.
Morse_decoder_rom	1, 2	Combinational A–Z Morse code lookup table.
FSM_letter	1, 2	Top-level control FSM sequencing comparator search and display.
sevenSegmentDisp	1	4-digit multiplexed 7SD driver (raw pattern / single letter).
sevenSegDisp	2	Extended 7SD driver supporting word view, letter view, and per-letter Morse view.
debouncer	1, 2	Shift-register button debouncer.
heartbeat	1, 2	Configurable-period clock divider ("tick" generator).
waitCounter	1, 2	Dual second-resolution timers (2 s / 5 s) used for inactivity timeouts.
counter	1, 2	Free-running address counter for the ROM search.
sevenSegmentDecoder	1, 2	BCD-to-seven-segment cathode pattern decoder.
button_pressed	2	Button-state helper for East/West navigation.
spot	2	Rising-edge one-shot pulse generator.

Board I/O map

Target board: Digilent Basys3 (Xilinx Artix-7, xc7a35tcpg236-1), 100 MHz onboard oscillator. Pin constraints are defined in each level's Basys-3-Master.xdc.

Signal	Direction	Level 1 pin	Level 2 pin	Function
clk	in	W5	W5	100 MHz system clock
btn_enter	in	U18	U18	Centre button — Morse dot/dash input
btn_reset	in	U17	U17	Reset button
btn_east	in	—	T17	Navigate to next letter (Letter View)
btn_west	in	—	W19	Navigate to previous letter (Letter View)
enableDisp	in	V17	V17	Slide switch — enable/disable 7SD output
switchDisp	in	T1	T1	Slide switch — raw pattern vs. decoded view
enableIn	in	R2	R2	Slide switch — gate button input
letterView	in	—	U1	Slide switch — enable per-letter browsing
led[7:0]	out	U16…V14	U16…V14	FSM phase / status indicators
ssdCathode[7:0]	out	W7…U7, V7	same	Seven-segment cathodes (incl. decimal point)
ssdAnode[3:0]	out	U2, U4, V4, W4	same	Seven-segment digit anode select

Getting started

1. Install Xilinx Vivado 2019.2 (or later).
2. Open the desired project:
   • Level1/level_1.xpr for single-character decoding, or
   • Level2/level_2.xpr for multi-character word decoding.
3. Run Synthesis → Implementation → Generate Bitstream.
4. Connect a Basys3 board over USB and program it via Vivado Hardware Manager.
5. Operate the board:
   • Flip enableIn on, then hold the centre button briefly for a dot or longer (≥3 s) for a dash.
   • Wait 2 s after your last press to let the system decode; the LEDs show progress and the 7SD shows the result.
   • Toggle switchDisp to switch between the raw entered pattern and the decoded letter/word.
   • On Level 2, flip letterView and use the East/West buttons to page through the letters of the current word.
6. Testbenches (TB_keypadProc.v, TB_comp_mem.v) are available under each level's sim_1 sources for functional simulation in Vivado's simulator.

Repository layout

Level1/                     Vivado project — single-character decoder
  level_1.srcs/sources_1/   RTL sources (FSMs, comparator, ROM, display, timers)
  level_1.srcs/sim_1/       Testbenches
  level_1.srcs/constrs_1/   Basys3 pin constraints (.xdc)
  level_1.xpr                Vivado project file

Level2/                     Vivado project — multi-character word decoder
  level_2.srcs/...          Same structure as Level 1, plus word/letter-view logic
  level_2.xpr

LICENSE                     MIT License

License

Released under the MIT License.