Web-Based Digital IC Tester

A full-stack, Web-Based Digital IC Tester built with a Raspberry Pi Pico and MCP23017 I/O expanders. It reimagines the classic, expensive digital IC tester as a modern, scalable hardware and software system featuring dynamic pin routing, truth-table verification, and a Web Serial API frontend.

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Part 1: Hardware Implementation

The Architecture: Brain vs. Muscle

This project splits the workload between a web browser and a microcontroller to overcome the storage and UI limitations of traditional embedded systems:

• The Brain (Web Frontend): A browser-based interface built with HTML/JS. It holds the infinitely expandable IC JSON database (truth tables, power pinouts) and handles the user interface.
• The Muscle (Raspberry Pi Pico): A "dumb" executor running MicroPython. It listens for JSON commands via USB serial, executes the raw I2C byte operations to the MCP23017 chips, and returns the physical logic results.

Key Features

• Digital Programmable Switching Matrix: There is no fixed wiring for VCC or GND. The firmware dynamically configures any of the 40 ZIF socket pins as a Logic High, Logic Low, High-Z Input, or Power Supply based on the selected chip's footprint.
• Web Serial API Integration: Communicates directly with the Pico via USB serial directly from Google Chrome or Microsoft Edge. No standalone desktop apps or drivers required.
• Truth Table Verification: Injects test vectors (stimulus) into the IC and compares the physical logic responses against expected states.
• Auto-Identify Mode: Features a brute-force logic scanner that safely queries unknown chips against the database to automatically identify the component inserted into the socket.

Hardware Requirements

• 1x Raspberry Pi Pico (MicroPython installed)
• 3x MCP23017 I2C I/O Expanders
• 1x 40-pin ZIF Socket (Zero Insertion Force)
• 1x Bi-Directional Logic Level Shifter (for 3.3V to 5V I2C safety)
• Digital Logic ICs for testing (e.g., 74LS00, 74LS08)
• Breadboard and Jumper Wires

Pin Mapping & Wiring

The ZIF socket is bottom-justified and mapped across the three MCP23017 chips to support ICs ranging from 14-pin to 40-pin footprints.

• Top Chip (0x20): Global Pins 0 - 15
• Middle Chip (0x21): Global Pins 16 - 31
• Bottom Chip (0x22): Global Pins 32 - 47 (Example: A 14-pin IC placed at the bottom of the socket utilizes the GPA and GPB ports of the 0x22 chip).

Theory of Operation

1. Safe Configuration: All pins default to High-Impedance inputs to prevent shorts when an IC is inserted.
2. Power Up: The web frontend sends the IC's power footprint. The Pico drives the specific VCC pin HIGH and GND pin LOW.
3. Vector Testing: The Pico iterates through every possible input combination defined in the truth table, measuring the output pin.
4. Conclusion: If the physical logic matches the database exactly, a PASS signal is sent to the frontend UI. The IC is then safely powered down.

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Part 2: Software & Simulation Implementation

Before hardware assembly, the entire testing matrix was modeled and validated using the Wokwi Simulator. This allowed for safe testing of I2C communications, memory mapping, and logic validation without risking damage to physical components.

Simulation Architecture

The simulation relies on a custom environment to accurately mimic the physical hardware:

• MicroPython (main.py): Handles the I2C scanning, pin mapping, and truth-table execution logic.
• Custom C-API Chips: Since Wokwi does not natively support all components, custom chip.c and chip.json files were written to emulate the exact behavior of the MCP23017 I/O expanders and the bi-directional Level Shifter.

Circuit Evolution & Routing

The simulation wiring underwent several iterations to ensure electrical accuracy and proper I2C addressing:

1. Initial Prototyping: The base circuit established the connections between the Pico, the three MCP23017 chips, and a target 74LS08 IC.
2. Level Shifting Integration: A custom level-shifter breakout was introduced to bridge the 3.3V Pico logic with the 5V MCP logic.
3. Final Circuit Diagram: The hardware address pins (A0, A1, A2) on the MCP23017 chips were strictly routed to GND and VBUS. This ensures the Pico can distinctly recognize them at I2C addresses 0x20, 0x21, and 0x22.

Testing & Validation Outputs

The MicroPython serial monitor successfully validates the core capabilities of the IC Tester:

1. I2C Scanning & Auto-Identification: Upon boot, the system successfully scans the bus and detects the three expanders. When set to Auto-Identify Mode, the script rapidly pulses test vectors against an unknown inserted chip, successfully matching the physical responses to the 74LS08 database signature.

2. Manual IC Testing (Pass Condition): When manually commanding the tester to check a 74LS08 AND Gate, the system steps through all 4 gates. The console prints the expected (Exp) vs. actual (Got) states for every truth-table row, resulting in a perfect PASS.

3. Fault Detection (Fail Condition): To prove the system catches bad logic, a 74LS08 chip was left in the socket, but the system was told to test it as a 74LS00 NAND Gate. The system correctly identifies the logic mismatch on every gate, throwing red X marks and halting with a final FAILED status.