Mike Coats' Spy! Break! Inject Is a "Monster-in-the-Middle" Board for Working with Four-Wire Buses
Simple passive board lets signals be rerouted to pin headers and test points for ease of analysis and injection.
Maker Mike Coats has designed a "monster-in-the-middle" board that aims to make it easy to sniff, inspect, and even override signals on any four-wire bus: the Spy! Break! Inject board.
"Inserting this board inline with any four-wire bus lets you spy on, break into, and inject signals. It's a purpose-built breadboard for reverse engineers," Coats explains of the device. "Removing jumpers and connecting wires to the pin headers allows signals to be routed away to a microcontroller for logging, relaying, proxying, and modification."
The simple board — entirely passive, with no active components required — uses spring-loaded Würth terminal blocks at either end to sit in the middle of a four-wire bus, capable of grabbing wires down to 30 AWG in diameter. Signals are brought out to pin headers designed for DuPont-style jumper wires for routing to external hardware, while hook test points at the bottom of the board target oscilloscope and other test tool probes.
Breaking the signals out is only one part of the problem, though: the board includes a jumper header in the middle, which allows any given wire to be broken from the Würth-to-Würth path and rerouted through the pin headers and test points. "Multi-meter probes can be connected across the rails to measure voltages," Coats adds of the board's features. "Current draw for a component can be measured by removing the jumper from the VCC rail and clipping an ammeter inline."
Coats has released design files for the board under the strongly reciprocal variant of the CERN Open Hardware License Version 2 on Codeberg; bare PCBs and full kits are available to order on his Tindie store at $25 and $35 respectively.
