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Binary Clock

A fully discrete binary clock built using 74LS-series logic and a crystal oscillator.
Tools/Technologies: KiCad / Fusion 360 / 74LS Logic / Crystal Oscillator / Through-hole Soldering / 3D Printing
Date: Spring 2023

Overview

This project is a fully discrete binary clock that uses 74LS-series logic chips, a 32.768 kHz crystal oscillator, and cascaded clock-division stages to produce a stable 1 Hz timing pulse. The divided pulse drives binary counters connected to multiplexers and decoders that display time through an LED matrix. The system operates from a 9 V battery and includes switches for power and manual time-setting, functioning similarly to a commercial digital clock.
The design intentionally avoids microcontrollers, demonstrating how fundamental synchronous logic can be used to implement real-time digital systems.

My Role

  • Designed and 3D-modeled the entire enclosure using Fusion 360.
  • Hand-soldered all components on a prototyping board, including LEDs, resistors, and 74LS logic ICs.
  • Co-designed the logic system and wiring with one teammate, including counters, multiplexers, and the LED display arrangement.
  • Integrated the crystal oscillator and clock-division stages, incorporating professor feedback on divider theory.
  • Assembled and tested the full system to ensure stable long-term operation from a 9 V battery.

Technical Challenges

  • Clock Division Accuracy: Achieving a clean 1 Hz signal required chaining multiple counter stages while managing propagation delay and ensuring synchronous behavior.
  • LED Drive Constraints: Ensured proper current-limiting and avoided overloading 74LS outputs while maintaining uniform LED brightness.
  • Switch Noise & Debounce: Manual time-setting introduced mechanical bounce, requiring careful wiring and filtering to prevent false increments.
  • Perfboard Routing Density: Managing the physical layout of several counters, decoders, resistors, and LEDs on a compact perfboard required thoughtful routing to minimize interference.

Key Design Decisions

  • Use of 74LS Logic: Selected to practice fundamental digital logic design instead of relying on a microcontroller.
  • Crystal Oscillator Timing Reference: Provided long-term stability and eliminated drift inherent to RC-based timing.
  • Custom 3D-Printed Housing: Improved structural rigidity, protected components, and added a polished appearance for portfolio use.
  • Battery-Powered Operation: Kept the device portable and simplified power regulation for TTL logic.

Results / Outcomes

  • The clock kept accurate time over long intervals until battery depletion.
  • All counters, decoders, and display outputs performed reliably with no measurable drift.
  • The enclosure successfully aligned the LED display and contributed to a clean, professional final product.
  • Strengthened skills in synchronous logic, debugging hardware timing issues, and compact perfboard assembly.

Visuals / Media