Open source trip computer design
OBDuino is an open source trip computer design based on the Arduino platform. An OBDuino may be assembled and customised by an electronics hobbyist; it displays information such as instantaneous fuel economy (e.g. miles per gallon, L/100 km or kilometres per litre), engine tuning parameters etc. on an LCD.
OBDuino utilises the On-Board Diagnostics interface found in most modern cars.
Features
- Most OBD-II PIDs or derived values may be displayed. Common values include
- Fuel: cost, used or remaining, wasted while idling, consumption, measured in mpg or l/100 km
- Engine: load, RPM
- Temperatures: coolant, air intake
- Vehicle speed
- Tank distance
- Remaining distance that can be travelled on the current tank of fuel
- Throttle position
- Battery voltage
- CAN status, for CAN protocol only, display TX and RX error
- Displays instantaneous values, average, maximum and minimum values calculated per trip, per outing, or per tank of fuel
- Menu system for configuring parameters
- Relatively cheap compared to commercial alternatives
- Customisable and extendable
OBDuino does not display or reset engine fault codes (which are available over the OBD interface).
Design
The key components of the design are:
- A microcontroller. One of the various AVR-based Arduino kits is typically used for this, although one of several Atmel AVR microcontrollers may be used directly in a custom OBDuino circuit.
- An interface to the car's management system, using the On-Board Diagnostics (OBD) connector found in most modern cars. This requires a cable and a circuit.[1] There are several variations of this circuit depending on the particular OBD protocol implemented:
- ISO 9141/ISO 9141-2/ISO 14230, using Freescale MCZ33290EF
- CAN, using MCP2515 and MCP2551
- Generic (SAE J1850 PWM & VPW/ISO 9141/ISO 9141-2/ISO 14230/CAN protocols), using an ELM327 from ELM Electronics. Although this gives a more versatile trip computer compatible with most modern vehicles, the ELM327 chip adds significant cost to the circuit and requires a significant supporting circuit for different protocols. It removes the complexity of interpreting the various OBD protocols.
- STN1110 which is software compatible with the ELM327. Unfortunately, this IC is not pin-compatible with the ELM327, therefore the circuit would require some changes.
- An LCD and three input buttons. A typical LCD is 2 rows x 16 characters or 4x20 character, based on the HD44780, with a circuit based on the mpguino circuit.[2]
- Microcontroller code. This is a C++ program based on the Arduino framework, called a Sketch in Arduino terminology. This is loaded on the microcontroller over a USB or serial interface using the free Arduino integrated development environment.
Many Arduino-based projects have either custom printed circuit boards available which include the AVR microcontroller (removing the need for an Arduino board), or extension boards that contain the extra circuit and that plug directly into the standard Arduino circuit board. No such PCBs are available for the OBDuino as of September 2009.
Project
The OBDuino project was started in 2008 based on the MPGuino project, with the desire to simplify wiring to the vehicle, instead of using the standard OBD-II socket that does not directly wire to the vehicle's fuel injection system and digital vehicle speed sensor, and to access the wide range of engine management data available using OBD.
The project is centred on the discussion forum[3] on ecomodder.com and the wiki and code hosting[4] provided by Google code, project is released under the GPL license.
The main OBDuino thread[3] on the eccomoder forum was started by jmonroe on 1 June 2008 as a fork of MPGuino discussions.
Magister posted an OBDuino announcement[5] to the Arduino forum on 4 December 2008.
As of September 2009, the OBDuino32K code credits these developers:
Main coding/ISO/ELM: Frédéric (aka Magister on ecomodder.com)
LCD part: Dave (aka dcb on ecomodder.com), optimized by Frédéric
ISO Communication Protocol: Russ, Antony, Mike
Features: Mike, Antony
Bugs & Fixes: Antony, Frédéric, Mike
The 32K in the obduino32K name differentiates the code targeted at the Atmega328 with 32k flash memory (i.e. Arduino 2009) version from the Atmega168 16k (Arduino 2008) version.