Morse Code Circuit

Analog-Logic Morse Code Decoder & Visualizer

A hobby hardware and logic design project that decodes Morse code input into discrete Dit (Dot) and Dah (Dash) shift register arrays using pure analog timing circuits and discrete digital logic, without requiring any microcontrollers.

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🚀 Overview

This project implements a temporal-logic state machine to parse Morse code inputs. By measuring the duration of a button press using an RC charging network and Schmitt-trigger buffers, the circuit discriminates between short pulses (Dits) and long pulses (Dahs), shifting them into separate 8-bit serial-in, parallel-out shift registers to display the incoming character pattern visually via an LED array.

🛠️ Circuit Architecture & Components

1. Integrated Circuits (ICs)

• U1 (74HC14): Hex Schmitt-Trigger Inverter (used for signal shaping, debouncing, RC timing discrimination, and clock-edge generation).
• U2 (74HC164): 8-Bit Parallel-Out Serial Shift Register (Dash / Dah sequence array).
• U3 (74HC164): 8-Bit Parallel-Out Serial Shift Register (Dot / Dit sequence array).

2. Passive Components & Semiconductors

• Resistors:
  • R1, R3 (10kΩ): Pull-up resistors for reset and input logic states.
  • R2, R4 (1kΩ / 100kΩ): Analog timing and isolation components for the RC charge/discharge network.
  • R5 (10kΩ): Edge-detector / clock-pulse network resistor.
  • R6–R10 (330Ω): Current-limiting resistors on the LED common-cathode/anode return paths.
• Capacitors:
  • C1, C2 (0.01µF): Switch debouncing and noise-filtering capacitors.
  • C3 (2.2µF): Core timing capacitor that integrates press duration for Dah discrimination.
  • C4 (10nF / 0.01µF): Differentiator capacitor used to generate a clean clock pulse on key-release.
• Diodes:
  • D1 (1N4148): Switching diode controlling charge/discharge pathways in the timing circuit.
• Displays & Controls:
  • SW1: Momentary push button (Master Reset).
  • SW2: Momentary push button (Morse Key Input).
  • LED Arrays (LED_Dual_AAK): Dual-color indicators displaying the shifted dot/dash sequences.
  • J1: 2-pin screw terminal / header for 5V DC Power Input.

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⚡ Power Requirements

• Operating Voltage: 5V DC regulated supply.
• All logic ICs belong to the 74HC High-Speed CMOS family (operating safely between 2V and 6V).
• Decoupling capacitors ($100nF / 0.1\mu F$) are recommended across the VCC and GND pins of each IC on the PCB layout to suppress transient voltage spikes.