Reverse-Engineering My Coffee Machine’s Serial Protocol with Wireshark

Reverse-Engineering My Coffee Machine’s Serial Protocol with Wireshark

By Ebuka Onah

It started as a simple curiosity: why does my coffee machine “think” for a few seconds before brewing? That delay felt like communication—not computation.

So I did what any slightly unhinged developer would do: I opened Wireshark and started sniffing traffic between the control board and its internal module.

Some people drink coffee. Others reverse-engineer how coffee is commanded into existence.

The Setup That Started It All

The machine exposed a serial interface through a hidden service port. I connected a USB-to-UART adapter and started capturing raw bytes.

  • USB-to-Serial converter
  • Wireshark for packet inspection
  • Screen session for live logging
  • Patience (the most important tool)

At first, it looked like noise. Then patterns started emerging.

When “Noise” Becomes a Protocol

Most embedded systems don’t send clean JSON or readable commands. They send structured binary messages. 

AA 55 01 03 10 00 7F
AA 55 01 04 20 01 8A
AA 55 01 05 30 02 9C

The AA 55 header kept repeating. That was the first clue: a framing signature.

Protocols rarely hide. They just refuse to introduce themselves politely.

Decoding the Command Structure

After hours of comparing state changes (button press → brew → stop), a structure became clear:

  • AA 55 → Frame header
  • 01 → Device ID
  • 03 / 04 / 05 → Command type
  • Payload → Brewing parameters
  • Checksum → Integrity validation

The machine wasn’t “smart.” It was just obedient binary logic.

The Moment It Clicked

I replayed a captured packet while pressing the brew button manually.

Same sequence. Same timing. Same payload changes.

That’s when it became obvious: the UI wasn’t controlling the machine. It was just translating user actions into serial messages.

Every “smart” appliance is just a conversation you haven’t decoded yet.

Building a Fake Brew Command

Once the structure was understood, I tried crafting my own packet. 

AA 55 01 03 10 01 80

I sent it back through the UART interface.

The machine responded instantly: it started brewing without touching the button.

What Broke First

  • Checksum mismatch caused silent command rejection
  • Timing sensitivity broke early experiments
  • Repeated commands triggered safety lockout
  • Wireshark filters became overwhelming without structure

Hardware is unforgiving. It assumes you are wrong until proven otherwise.

What This Actually Teaches

This wasn’t about coffee. It was about abstraction layers.

  • UI layer: Buttons and LEDs
  • Firmware layer: Command translation
  • Hardware layer: Electrical execution

Most systems you use daily are just stacked translations of intent.

Reverse engineering removes the illusion of simplicity.

Why This Matters Beyond Coffee Machines

The same patterns exist in:

  • IoT devices
  • Smart home systems
  • Car ECUs
  • Industrial controllers

If it has a chip, it is speaking a protocol.

Final Insight

Once you see systems as communication layers instead of “magic devices,” everything changes.

You stop asking what a device does—and start asking how it talks.

Understanding a machine is just learning its language. Everything else is implementation detail.