The '86 BMW I'm working on has a fuel economy gauge:
(http://www.filehive.com/files/081127/tacho.jpg)
Haven't tested it yet, but I suppose it works the same as the electronic tachometer which feeds on a symmetric square wave. I understand that the P259 is configured to control the tach for this.
Of course computing for fuel economy requires a combination of a speed signal and probably injector duty cycle. The Motronic ECU which the BMW uses has a vehicle speed signal input (VR sensor from rear wheel), so it's straightforward for it to compute for fuel economy.
Anyone have any idea how to implement such a scheme using VEMS?
I think there's something to do with vacuum with that gauge.
In order to find a solution you really need to find what signals go into that gauge.
IÃ,´ll just tell you how it works ;)
It is a square wave but itÃ,´s non linear so any output would have to be on a curve.
http://uk.youtube.com/watch?v=S5KwL2DUkro
I belive the boost output meter in current firmware would have to be further developed to work with the bmw gauge.
ItÃ,´s also not body style comparable as there is a coding chip and other engine and diff related calculations in the dashboard going on,.
At less than 25mpg do you really need a consumption gauge anyway, cant you just use the fuel level gauge instead :D
;) ;)
There are templates out there now to turn that gauge into a
oil temp
oil pressure
boost
could be wideband if wanted
all kinds, but I think those will all be seperate purchasable thing so no standalone relations.
Quote from: gunni on November 27, 2008, 09:05:15 AM
IÃ,´ll just tell you how it works ;)
It is a square wave but itÃ,´s non linear so any output would have to be on a curve.
http://uk.youtube.com/watch?v=S5KwL2DUkro
I belive the boost output meter in current firmware would have to be further developed to work with the bmw gauge.
ItÃ,´s also not body style comparable as there is a coding chip and other engine and diff related calculations in the dashboard going on,.
Gunni, as usual great info. I think I can borrow a signal generator so I'll post here how it maps frequency to output. My car's also in L/100km, just picked a photo off google images and got that one with the MPG counter.
Quote from: gunni on November 27, 2008, 09:05:15 AM
There are templates out there now to turn that gauge into a
oil temp
oil pressure
boost
could be wideband if wanted
all kinds, but I think those will all be seperate purchasable thing so no standalone relations.
I like this idea. I'll probably settle with oil temp, oil pressure or fuel pressure (when the turbo goes in there).
I guess there's no programmable frequency output in the current firmware right? If not, maybe a simple voltage-to-frequency circuit would do well at the moment. I think I have a spare 100psi, 0-5V output pressure sensor lying around.
Thanks everyone!