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I want to build a custom MPG display to put in my rear window to let other drivers on the road know how many miles per gallon I am getting.

Has anyone done this? Has anyone tried?

I have a bit of experience with electronics, robotics, and computer programing. At one point I remember seeing online some software that allows you to plug your laptop into your insights computer and get realtime data such as MPG. Now I can't find it again.

Also, I have heard that cars use a system called CAN to communicate data amongst the various computers and electronics. Does anyone know how to tap into this system? How the data is structured and how to get at the MPG data?
 

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Welcome,

Well I am useless here (and some will say many other places, too), but will be rooting for you since I have brought this up a few times myself.

The OBD port on the bottom of the dash, under the steering wheel, is the interface. There are units that will plug in to this port and give you access to a lot of data. I don't know if the instantaneous mpg is included, since I don't have one of these tools.

I am sure one of the folks here that has one will pitch in soon.
 

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This would be a great addition for Insights. I have thought about this myself but don't know how to do it. I wish someone would start selling them.
 

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Hemm, if you figure it out, please please please detail it somewhere. I wanna do the exact same thing but don't have the expertise to do it.

If the OBD port sends out RS232 data you should be able to write a little app, or build a little box, that would ignore the unneccesary data. I havent had any time to look into this at all. If you get a copy of the OBD software you may be able to reverse engineer it.

You could also hook something up in the line to the FCD that would send back the instantaneous or AMPG to an LCD or LED matrix.
 

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I looked at the shop manual over the weekend, and it appears that all the info for the mpg display (and most of the other displays on the dash) is actually calculated in the ECU, and sent to the dash display over a single wire (#5 in the ECU's B connector, IIRC) as "pulses". So if someone had a recording oscilliscope they could hook to that line, or could otherwise crack the encoding used, then it should be simple to build a display unit that just checks for the required codes.
 

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I like the idea of this kind of display, but my bigger question is whether it is legal to have an ever-changing motion display on your car? Wouldn't it be considered a distraction to other drivers, and therefore not allowed by the local authorities?
As much as I see advertising on vehicles, I have never seen it "in motion". (Other than those message boards on busses that show you what route they're going.)
 

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Though the instantaneous display would be more dramatic (think of the guy behind as you suddenly jumped to 150MPG) perhaps the seemingly more static Average MPG would be a better idea.

Or have a little display that reads off the current trip mileage. This would be nice if, like me, you reset the trip odo whenever you fill up. You could have the display and right next to it have "- on ten gallons of gas!"

Or you could put the display behind the smoked glass of the lower rear window. It would not be as visible. Or you could put a switch in that turns the display off when a copper is behind you. Or power it on the same circuit as the brake lights so it only shows up when you press the pedal.

Just some ideas...
 

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You think the instantaneous can be converted to numerical info? That's what I would like.

The display would not be "moving" but would be constantly changing. Of course, it would need a "kill switch" just in case, since I am sure it isn't DOT approved.
 

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This is where we need a Honda Rep. I am guessing that the instantaneous is numerical by nature and we only normally see it as a bar graph. I think it sends that data out through the OBD port which is sending numerical data anyway, sooooo....

Of course i'm probably wrong.
 

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Speaking of MPG gauges, I've been trying to find some sort of gauge I could put on my '97 civic to try to get better mileage out of it. I've searched all over without any luck. Maybe there aren't enough conscientious people for there to be a market on cars that don't come equipped with them. Even so, any help finding one would be appreciated. :)
 

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Well it is a long shot (but I used it many years ago), there is one type of gauge that could help you. It basicaly gives you the load on the engine. A vacuum gauge.

The vacuum gauge connected to the intake manifold will give you an instantanious response:

You need to keep the vacuum pressure a high as possible. A high vacuum pressure means a high MPG while driving.

When the pressure is low it means that you are going to the WOT possition and low MPG while you drive

Note: Of course when I write high pressure I mean high vacuum pressure meaning a lower pressure than the atmospheric pressure.
 

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What if the gasaholic vehicles had this feature too? :D
 

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FinalHeven,
I've been trying to find some sort of gauge I could put on my '97 civic to try to get better mileage out of it.
This topic came up before (I can't remember if it was here or at GreenHybrid.com) and xcel found a gauge that was produced in Europe that had some of these capabilities. From what I remember it was geared toward commercial use so that companies could keep an eye on their employees. I don't remember the name of it, or even how transferrable the technology was to the US.

Man! I've got to find that post. When I do, I'll share it here.

***EDITED***
A-HA!
I knew I'd find it. It was in a discussion at Green Hybrid about Non-hybrids missing EPA estimates too
http://greenhybrid.com/discuss/index.php?showtopic=654&st=20
Specifically xcel's Jun 10th 2004 @ 3:09 PM post.

In that thread xcel posted a link to a company called Drive Systems that is in Norway.
Here's the link: http://driveright.as/

They make a gauge called the Econen that has many of the features you would need to improve mileage if your car did not come factory equipped with a gauge.

Interesting to read about...

Safety Score provides instant evaluation of driver's performance and coaches driver to improve safety. Lower risks for work-related accidents by improving driver awareness and safety. Safe limits set by the company can be consistently applied throughout the fleet.
Drive Costs Down
When a driver is more aware of his tendencies and surroundings, savings follow. Alert drivers reduce wear and tear through safer braking patterns and conservative actions. No employee time spent on data entry or mileage report. Promote fuel-efficient driving by discouraging speeding and rapid acceleration.
 

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hemminger8 said:
I want to build a custom MPG display to put in my rear window to let other drivers on the road know how many miles per gallon I am getting.
I did see something that you can put in your rear window like a little message board, and you can type any message you want to appear. I guess you could type in whatever your mileage happens to be at the moment. Can't remember where I saw it or what it's called.
 

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ericbecky said:
I like the idea of this kind of display, but my bigger question is whether it is legal to have an ever-changing motion display on your car? Wouldn't it be considered a distraction to other drivers, and therefore not allowed by the local authorities?
Would no different than having your turn signal on or those moving lighted plate frames.
 

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The other way around, the more vacuum, the less gas is being used.

You have good vacuum when the throttle is closed (high MPG).
You loose vacuum when the throttle is opened (low MPG).
 
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