Backplane

TTL Logic Analyzer

Breadboard and PCB-based logic analyzer built from discrete 74xx TTL logic, SRAM, and multiplexed LED matrix displays.

Overview

This project aims to build a fully discrete logic analyzer without using a microcontroller. The analyzer captures digital bus states into SRAM and displays captured samples on multiplexed LED matrices.

Project is currently in a state of active prototyping.

*This repository also contains a closely related project using an MCU-based design with 24 channels.

Features

• Fully TTL-based architecture
• SRAM-based sample capture
• Multiplexed LED matrix display
• External/internal clock modes
• Planned trigger and halt functionality
• Modular PCB-based design

Current Status

Current prototype supports:

• 64ish x 8 sample memory subsystem on a self-designed PCB
• LED matrix display driver

Known issues:

• Limited memory
• Pull down resistor problems

Architecture

Main subsystems:

• Capture memory subsystem
• Address/control logic
• Clock generation and edge conditioning
• Display subsystem

Relevant Simulation Subcircuits

• analyzer_7400.circ — 74xx IC Implementation
  • mem_64x8: Full memory subsystem test built from 74xx-style chips using four ram_unit subcircuits.
  • ram_unit: 16x8 RAM unit built from 74xx-style chips; used as the building block for mem_64x8.
  • disp_16x16: Limited-capacity display subsystem test; does not yet include the physical driver circuitry needed for hardware.
• analyzer_ttl.circ — Abstract Logic Implementation
  • mem_64x8_async: Asynchronous version of the 64x8 memory subsystem; same capacity as the final intended design.
  • disp_16x32: Full-capacity display subsystem test.

More detailed documentation:

• Analyzer Architecture
• Build Log
• Simulation Subcircuits

Repository Structure

docs/                   Docs and architecture notes
images/                 Build photos and diagrams
pcb/                    KiCad PCB projects
simulations/            Logisim simulations
attiny-logic-analyzer/   Related MCU-based project

Hardware

Main IC families/components:

• 74xx logic family chips
• ULN2803 and UDN2981

Future Plans

• Expand memory depth
• Modular memory pcb
• Trigger logic
• Improved clock conditioning
• PCB-based final implementation

If the project expands beyond basic TTL hardware, plans may include

• USB interface
• OLED display
• Many more channels
• Higher sampling rate

License

MIT License