A Real-Time Fuel Consumption Monitor

Jeff Bachiochi’s real-time fuel consumption monitor for his Jeep.

Circuit Cellar columnist Jeff Bachiochi has enjoyed driving his wife’s Prius, in part because of the real-time feedback it gives him on the miles per gallon he is getting. It made him aware of how he could save gas with simple and immediate adjustments to his driving style.

With that in mind, he thought it would be a good idea to build an effective and affordable monitoring device that would give him the same real-time mpg for his Jeep.  After all, he can’t always borrow his wife’s car.

In the June issue, he shares what he came up with for an onboard diagnostics display. He explains below how he tapped into his own experience, as well as that of another Circuit Cellar author, to build the device for Jeep

“In the summer of 2011, I presented a three-part series about the on-board diagnostic system (OBD-II) built into every automobile produced since 1996 (Circuit Cellar 251–253)….”

“In 2005, Bruce D. Lightner wrote an article about his winning entry in the 2004 Atmel AVR design contest (“AVR-Based Fuel Consumption Gauge,” Circuit Cellar 183, 2005). Lightner’s project altered an analog tachometer gauge as a display for miles per gallon. I wanted to show a little more information, so my project uses a Parallax Propeller microcontroller to interrogate the OBD interpreter and drive a composite LCD.

“You can get a composite color display from Parallax or an online source. While I had a small 2.5” display to work with, I was looking for something a bit bigger. For less than $50, I found a 7” LCD, which happened to be combined with a camera (for mounting on a vehicle’s rear license plate frame)…

“I dug out my Propeller Proto Board and blew off the dust…. The Propeller microcontroller design includes eight 32-bit parallel processors (i.e., cogs) and peripheral support, including access to the 32 I/O pins, two counters, and a video generator per cog.  It is the video generator support that makes this project possible with a minimal component count…. only three resistors are required to develop a composite video output.“

To read more about Bachiochi’s OBD device, check out his article in the June issue.

 

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