diy mpg gauge - Fuelly Forums

Click here to see important news regarding the aCar App

Reply
 
Thread Tools Display Modes
 
Old 07-08-2007, 08:16 AM   #1
Registered Member
 
skewbe's Avatar
 
Join Date: Jan 2007
Posts: 771
Country: United States
diy mpg gauge

Update, skip ahead to a working model:
http://www.gassavers.org/showthread....32#post6473232


It seems a simple enough task, take a vehicle speed sensor "reading" and divide it by the injector duty cycle and put it on a meter. In fact my el-cheapo tach/dwell meter has both circuits in it (and a meter) and could be made to reflect vehicle speed (perhaps with an op amp on the vss) or injector duty cycle (which probably isn't much more than an inductor). Throw in some pots for calibration and an op amp to combine the signals and...

So has anyone come up with a simple mpg gauge circuit for the masses? I suppose digital would be better (i.e. keep track of every duty cycle for every vss pulse and add a "trip" type function to it), but I kind of like the "gomi"-ness of dissecting my old tach/dwell meter and making an mpg gauge out of it

Thoughts?

P.S. Scangauge is in my wifes hands and I don't have another $160, that's why I'm considering this , though something for the DIY sector would be useful.
__________________

__________________
Standard Disclaimer
skewbe is offline   Reply With Quote
Old 07-08-2007, 09:06 AM   #2
...
 
Join Date: May 2007
Posts: 425
Country: United States
Came across a link on pg 4 & 5 has the circuit diagrams(originally posted by retrorocket) . It appears to use a sunpro tach . Add a vaccum gauge along with some fabbing skill you *might* save a few dollars .
__________________

MnFocus is offline   Reply With Quote
Old 07-08-2007, 09:32 AM   #3
Registered Member
 
skewbe's Avatar
 
Join Date: Jan 2007
Posts: 771
Country: United States
Yah, that would be an obd approach, I was thinking analog stuff (and about $5 in parts added to my extremely simplistic sunpro dwell/tach). Mebbe those days are gone?
__________________
Standard Disclaimer
skewbe is offline   Reply With Quote
Old 07-08-2007, 09:43 AM   #4
...
 
Join Date: May 2007
Posts: 425
Country: United States
Didn't SVOboy(I think it was anyway) do a fuel gauge with a dwell tach ? I'd be willing to bet that the same thing *can* be done the way you described . You just need to take the time to get the calibrations down .
MnFocus is offline   Reply With Quote
Old 07-08-2007, 11:22 AM   #5
Team GasMisers5!
 
landspeed's Avatar
 
Join Date: Nov 2006
Posts: 440
Country: United States
The cheapest way to do it would be to...

(1) Get an Atmel processor, and programming kit from ebay. Get the flash-reprogrammable processor, so you can experiment.
(2) Find some code + circuit diagram for wiring it to a calculator screen (8-digit LCD)
(3) Connect it to the Auto power supply (using the info in that PDF). Use code to simply read the injector pulse duration, and the vehicle speed sensor reading.
(4) Have one or two buttons on it. You could make a simple user interface, so you can 'reset' the 'TANK' when you refill, and reset the 'journey' each time you make a journey. Display instant MPG on the left of the calc display, and tank/journey MPG on the right hand side!

This is the basic idea behind the SuperMID, except that a lot more work has gone into it, in particular in interfacing it to a much more complicated display.
__________________

Team GasMisers5 - #1 for first three rounds of the original GS Fuel Economy Challenge
Miles displaced by e-bike since 1 Jan 2008: 62.6 (0 kWh used)
Hypomiler
landspeed is offline   Reply With Quote
Old 07-08-2007, 05:43 PM   #6
|V3|2D
 
thisisntjared's Avatar
 
Join Date: Mar 2006
Posts: 1,186
Country: United States
Send a message via AIM to thisisntjared
Quote:
Originally Posted by landspeed View Post
The cheapest way to do it would be to...

(1) Get an Atmel processor, and programming kit from ebay. Get the flash-reprogrammable processor, so you can experiment.
(2) Find some code + circuit diagram for wiring it to a calculator screen (8-digit LCD)
(3) Connect it to the Auto power supply (using the info in that PDF). Use code to simply read the injector pulse duration, and the vehicle speed sensor reading.
(4) Have one or two buttons on it. You could make a simple user interface, so you can 'reset' the 'TANK' when you refill, and reset the 'journey' each time you make a journey. Display instant MPG on the left of the calc display, and tank/journey MPG on the right hand side!

This is the basic idea behind the SuperMID, except that a lot more work has gone into it, in particular in interfacing it to a much more complicated display.
so how much do you think that will run??? if its less than $50 i might just have to try it...
__________________
don't waste your time or time will waste you
thisisntjared is offline   Reply With Quote
Old 07-08-2007, 09:17 PM   #7
Registered Member
 
sonyhome's Avatar
 
Join Date: Jul 2007
Posts: 150
Country: United States
Looking at the Mnfocus linky, I'd say the design could be simplified for a laptop:

There's 1 signal line from the ODB-2 picked up. Just pass it on to a laptop's serial port and have a program scan that serial port and do the computation, logging, and display.

That way it's ALL SOFTWARE, with $2 worth of parts. May need a pull down 12V->5V resistor bridge, or at worst an op-amp to decouple it all.

Just need a guy who knows how to code with visual basic or visual C a serial port reader...

If you wanna do it digital, replace their analog display with a cheap LCD bar display.
__________________

sonyhome is offline   Reply With Quote
Old 07-08-2007, 10:24 PM   #8
Registered Member
 
skewbe's Avatar
 
Join Date: Jan 2007
Posts: 771
Country: United States
Yah, the laptop->obd route is a well traveled path. Problem is obdii is a hodgepodge of protocols, and laptops aren't exactly cheap.

Also, I'm not ready to sort out PICs and deal with programmer compatabilities,specs,etc.


However, there may still be a dirt cheap option for iso, an old blackberry 957 perhaps (or mebbe a serial based palm) and something to convert 5v<->12v. In that way it is relatively easy to program/reprogram and comes with a display,input system, and a serial port based on the windows iso stuff:
http://www.andywhittaker.com/ECU/OBD...9/Default.aspx
BUT, it ony works with iso vehicles.



Here is another laptop idea, tap into the vss and injector pulses via the line-in right and left channels on the sound card and sort it out from there. They are basicaly A/D converters.
__________________
Standard Disclaimer
skewbe is offline   Reply With Quote
Old 07-09-2007, 12:13 AM   #9
Registered Member
 
sonyhome's Avatar
 
Join Date: Jul 2007
Posts: 150
Country: United States
Most people have laptops nowadays, and all have serial ports.

If there's an explanation of what to monitor on the ODB-2, then a simple program can be made, which then will be ported etc.

I'll ask a friend when I have a chance if he knows free PC software to monitor ODB2... Maybe we can find a free one that does the trick or can be modded for FE analysis.

Google Examples:

http://www.er-forum.de/obd-diag-dl
But it needs:
http://www.obdpros.com

http://jdash.ludicrous-speed.com/wik....php/Main_Page
http://www.tactrix.com/

http://www.scantool.net/?mode=displa...rd&#37;20Party

A good explanation:

http://www.thinkythings.org/obdii/
__________________

sonyhome is offline   Reply With Quote
Old 07-09-2007, 03:21 AM   #10
Team GasMisers5!
 
landspeed's Avatar
 
Join Date: Nov 2006
Posts: 440
Country: United States
Quote:
Originally Posted by thisisntjared View Post
so how much do you think that will run??? if its less than $50 i might just have to try it...
No idea, but, I know I could get the raw materials for $50 if I look around on ebay + other places. LCD screens seem quite expensive, but, if you find somewhere that sells simple calculator ones, it should be pretty cheap.
__________________

__________________

Team GasMisers5 - #1 for first three rounds of the original GS Fuel Economy Challenge
Miles displaced by e-bike since 1 Jan 2008: 62.6 (0 kWh used)
Hypomiler
landspeed is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Not very precise mpg calculation larjerr Fuelly Web Support and Community News 4 08-20-2012 01:03 AM
epa estimates cseverens Fuelly Web Support and Community News 2 06-09-2010 03:48 AM
Keeping my distance in traffic khurt General Fuel Topics 8 09-07-2008 03:23 AM
Electrical power and cars. DracoFelis Automotive News, Articles and Products 2 09-16-2006 01:31 PM
"active" aero grille slats on 06 civic concept MetroMPG General Fuel Topics 21 01-03-2006 12:02 PM

» Fuelly iOS Apps
Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 02:11 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.