Introduction

Reverse engineering a printed circuit board (PCB) can be a very useful skill for hardware hackers and engineers. Being able to understand how a circuit works by examining its PCB allows you to discover design techniques, find manufacturing flaws, learn from others’ work, repair boards, and repurpose components. While advanced skills and equipment make the process faster, it is possible to reverse engineer simple PCBs with basic tools and some patience.

In this guide, we will walk through the steps involved in reversing a PCB from start to finish:

Overview of the Reverse Engineering Process

• Visual Inspection of the PCB
• Identifying Components
• Tracing Circuit Connections
• Creating a Schematic
• Analyzing the Schematic

Step-by-Step Guide

Below we dive into each step of the process in detail, using an example PCB from a basic LED throwie project.

Visual Inspection

The first step is a quick visual inspection of the PCB to get acquainted with its layout. Take note of:

• Number of layers – Most consumer PCBs are 2-layer while more complex ones can have 4+ layers.
• Component placement – Look for integrated circuits (ICs), connectors, passive components like resistors/capacitors.
• Traces – Follow the copper traces connecting components.
• Silkscreen – Printed labels can identify components and functions.
• Vias – These connect traces between layers.
• Text – Notes from the board designer. -Anything else unique about the board.

This gives you a rough idea of the board’s complexity and where you should begin tracing connections.

Identifying Components

The next step is to identify the key components on the PCB. These typically include:

Integrated Circuits (ICs):

• Microcontrollers – e.g. Atmel, PIC, ARMs
• Memory – ROM, RAM
• Logic/interface ICs – buffers, drivers etc.

Discrete Components:

• Transistors – BJTs, MOSFETs, IGBTs
• Diodes
• LEDs
• Resistors, capacitors, inductors

Other:

• Connectors/sockets – ISP, USB, headers etc.
• Crystals, oscillators
• Buttons, switches, sensors
• Power/ground planes

Use online references like datasheets to identify component packages and match their designators on the PCB silkscreen. For ICs, look up the part number.

Tracing Circuit Connections

With the key components identified, we can start tracing circuit connections between them. This is the most time-consuming part of reverse engineering a PCB. We use the following techniques:

Follow Copper Traces:

• Visually follow the copper traces connecting components. Watch out for vias.
• Verify connections with a multimeter in continuity mode.

Identify Planes:

• Power and ground planes have large copper areas.
• Use a multimeter to verify connections to pins/pads.

Consult the Schematic:

• Most boards have a reference design you can look up.
• Gives you a shortcut for deciphering complex sections.

Creating a Schematic

Once the tracing is complete, we can start drafting a schematic diagram of the PCB. This is an abstract representation using symbols to illustrate the components and connections. It removes the complexities of PCB layout and makes the circuit behavior more clear.

Use CAD software or draw by hand to create the schematic. Standardize symbols and neatness as much as possible. Identify all component values and designators. Title the schematic, mark inputs/outputs, and include a legend if necessary.

Analyzing the Schematic

With the schematic complete, we can now analyze the functionality of the circuit through visual inspection and simulations.

To understand what the circuit does, follow the flow of signals between components. Identify key functions like:

• Power – Source, conditioning, and distribution.
• Microcontroller – I/O, timing, peripherals used.
• Sensors and inputs.
• Outputs – Motors, lights, communication interfaces.
• User interfaces – Buttons, switches, displays.

For complex circuits, simulate the schematic in SPICE software. This allows you to visualize voltages and probe signals.

With an understanding of the core functionality, you can now leverage this PCB design for your own projects!

Frequently Asked Questions

Here are some common questions about reverse engineering PCBs:

What tools do I need to get started?

At minimum, you need a multimeter to trace connections and verify component values. An inspection microscope helps examining