Designers encountering challenges with testing equipment via the OBD vehicle diagnostic port often face limitations, especially when a full-sized car isn't readily available nearby. Fortunately, there's no need to invest in costly professional gear to tackle the task. The MiniSim OBD simulator project from 2010 offers a budget-friendly and effective solution. Although there are more recent solutions out there, you can learn a lot from this interesting project.  

OBD Simulator Circuit

The ATmega8-based MiniSim OBD simulator efficiently replicates communication from a vehicle's OBD port and supports four of the most widely used OBD protocols. It serves as an invaluable tool for individuals engaged in OBD hardware or software development, as well as for general testing purposes.

The designer explains, "The circuit consists of a microcontroller with firmware, MOSFETs and comparators to perform the necessary voltage level shifting (5 V/12 V). The pots allow control of the simulated vehicle speed and engine RPM."
MiniSim OBD Simulator circuit
The simulator circuit features an an ATmega8 microcontroller clocked at 6 MHz
The pre-programmed MiniSim OBD simulator controller can implement four protocols and four trouble codes. Additionally, it is possible to configure 11 other trouble codes by means of the OBD2 interface. Specifications:
  • Four predefined protocols: KWP2000 Fast Init, KWP2000 Slow Init (5-Baud Init), ISO9141-2, and PWM J-1850.
  • Protocol selection using DIL switches
  • Four predefined error codes
  • Up to 15 configurable error codes
  • Sensor data for speed and rev count adjustable by potentiometer
  • MIL generation by pushbutton
  • “Connect” and active “MIL” indicators
  • Freeze frames store sensor data when MIL is generated.
  • Several assembly options
Sample PCB with mounted OBD connector
A sample PCB with a horizontally mounted OBD connector

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Folker Stange and Erwin Reuss's article, "OBD2 Mini Simulator," first appeared in Elektor 6-2010. If you are an Elektor Member, you enjoy ElektorMag, an Elektor Store discount on most products, and full access to Elektor’s online library, which includes this article and many others. If you don’t yet have a membership, take one out today!

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