Blog
Microcontroller arrived....
Date: 2/6/2008


I'm going to see if I can program it to display current economy figures in my car using the OBD-2 connector.
Comments:
Josh
02/06/2008 4:50am
Ooh, that looks nifty. That looks to be some sort of AVR processor with some other stuff on it. Is that a ready made OBD-2 scanner, or do you have some software ideas for doing the interfacing?

I looked into that once, let's see, grab some info from the MAF sensor, combine that with the known fuel to air ratio for your vehicle (unless you can happen to get that from the system as well) then look at your current speed, do some math and Robert's your father's brother.

I'd really be interested in knowing how this turns out.
fret
02/06/2008 4:56am
This stuff is all from futurlec. The main micro controller is the AVR stamp.

But I ordered 2 rs-232 converters (12v/5v interfaces for interfacing with a computer + obd), some LED 7 segment displays, an LCD display (if I'm feeling adventurous later) and some serial programming interfaces and cables.

I've also got a breadboard and an OBD-2 plug kit.
ClassicMiniFreak
02/06/2008 7:13pm
Hey Fret,
you sure have a break comming to do something that is fun.

But - if I may say this - do not expect the economy figures to give you the slightest real world help. If you could program so it also tells you what mpg you COULD be getting out of the current situation would help - IF there was no traffic. But as there is traffic, you would only want to jump out and kill someone.

Also, you may likely spend some good overtime to get wierd peaks out of the display without cutting out data.

The reason I say this (please follow line of thought):

To get optimum mileage per gallon you must, in order to -
1) accelerate:
allways in gears that keep the engine running within RPM range of peak torque, apply full throttle. (no use for less, as the ECU optimizes the fuel mixture!)
2) cruise in traffic (at determined speed):
use highest gear / lowest possible RPM w/o letting engine knock. Period!
3) cruise on highway (at economical speed):
in highest gear, choose speed just below engine's RPM of peak torque.
4) slow down:
never brake. Get out of gear and let decelerate to the right speed. Never accelerate so much you need to brake later on. If your car has an up-to-date ECU with throttle cutoff you can apply the engine brake, at the cost of (almost negligable) wear through reverse forces in all the gearing and bearings.

As you can imagine, traffic only lets you do 2) and 3) a noteworthy part of time. You are stuck with the bulk and their speed limits. If not, your economat will help only in 3) to give you the optimum RPM below max torque. And that would only ever change slightly with different winds.

The best real world thing you can do is get a tachometer (if not installed) and know the engine's torque diagram (or RPM range of max torque). Honestly.
And get a lightweight car w/o AC and all that "power extra" stuff, but they are not made any more. A Ferrari weighs almost about 2 Minis.

I hope I did not spoil a toy now, but you are pretty much grown up... ;-)
Arick
 
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