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I don't read German, but the schematic that is link is pretty self explanatory. I assume the thing will change to mpg. Cool project, and pretty simple concept. I may try to do this next year. If I can't find the parts referenced it should be pretty simple to substitute any flow sensor that outputs in pulses and adjust the circuit for any differences in calibration.

http://11109.rapidforum.com/topic=110775193806&search=sigma

2 caps, 3 resistors, an 8 volt regulator, an op amp, and some sort of IC!
There's nothing to this thing.
Depending on what that 4020 is and how much the sensor costs, anybody could throw the circuit together for pennies. Wonder what the sigma BC700 is and what it costs?

Looks like the meter sends a signal that is amplified by the opamp, then it feeds into the IC logic (a timer?), then that just feeds out to the Sigma. Definitely simple.

[reading further]
Hmmm - 113 DM is about $85 US. That's for everything.
These are 1996 prices too, mind you.

The Sigma is listed at 30DM or $23 US
the flow meter is 72.50 DM or $54 US
the rest of it is literally a few cents per piece at radio shack, (or free out of that old tape deck...)


Is the sigma just an electric bicycle tach? Should be able to get one of those anywhere for $10 or less.
Wonder if you could salvage a flow meter from something?
What would it's original/intended use be, I wonder?

I'm supposed to be getting an unwanted moped -- this would be a very cool addition!

I'm guessing that the components basically feed a signal into the sigma which fools it into showing an approximation of L/100km instead of RPMs. If that's the way it works you might be able to change out some of the components (or choose a different cmos, maybe?) that times the signal differently to come up with MPG.

I'm definitely going to look into this thing.

Yep - the BC 700 is a bicycle computer. It uses a wheel mounted magnet and a fork mounted sensor to determine speed.
http://www.floribamariders.com/wibel1.htm

So any cycle computer capable of this would probably work.

Now the tough part is the flow meter.

Conrad Electronics has an english website
http://www1.int.conrad.com

I did a product search for "126055-44"
and found the following

Inductive pulse generator
Article No.: 126055 - I5

Price just 39,31 EUR
piece(s)
Hose connection 6 or 9 mm, measurement range: 0.025 - 2.5 l/min.
The advantageous combination of materials of POM (Hostaform C), ceramically bound magnets and a polished, hardened stainless steel shaft offers optimal smooth running characteristics with high chemical stability range. Due to the sinusoidal output signal of the inductive pickup system, this sensor is ideal for the direct actuation of moving coil display instruments.
Technical data: Materials: POM (clear), FKM, NP · Ceramically bonded magnets · Connection: Hose dia. 6 mm and dia. 9 mm ·
Dimensions 77 x 22 x 42 mm · Sinusoidal output signal (the generated frequency is proportional to the quantity/time unit) · Temperature range -10 to +80 ºC (short-time up to 120 ºC) · Operating pressure/bursting pressure: 10bar/> 18 bar (H20 at +22 ºC) · Measurement range from 0.025 - 2.5 l/min.


So I guess when the carb sucks, a magnet moves and a pulse is created.
Conrad appears to be European only, but we should be able to take this info and source something similar in North America...