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[DPRG] Sensor ideas

Subject: [DPRG] Sensor ideas
From: A. Scientist angryscientist at gmail.com
Date: Thu Jan 7 08:35:53 CST 2010

How about an acewell fuel sending unit? Looks like they might be a bit
pricey though as they arent a US company. I see a few on ebay for ~$70AUD.

On Wed, Jan 6, 2010 at 5:38 PM, Sluggy! <sluggy9912 at swbell.net> wrote:

> Greetings, All!
> Long time, so seize. I have been a-lurking, though....
> Whilst lurking, I am doing another EFI conversion, this time on an air
> cooled VW engine. http://msruns.com/viewtopic.php?f=88&t=22894
> One of the problems I need to solve is operating the fuel gauge.
> The instrument I have http://tinyurl.com/ykje3lc wants to read a
> resistance between 0 and 100 ohms corresponding to the level of fuel in the
> tank. Since the tank is basically a hand fabricated 1 foot cube, there is
> not really a factory tank sensor that is actually made for it, at least not
> a cheap one. I am investigating salvage sensors, but it would be nice if I
> could use the one that is already on my fuel pump.
> The fuel pump I'm using is an in-tank unit that was salvaged from a
> Kawasaki motorcycle, a model that is equipped with a fuel gauge. The stock
> sensor, however, is basically a variable capacitance sensor. At this
> writing, I don't know what the range is, other than either empty or full is
> approximately double the capacitance of the other state. I need to convert
> that capacitance into a variable resistance. There is a chance that a
> variable voltage may work; I will have to investigate that separately.
> I'm contemplating a circuit that converts capacitance into either a
> pulsewidth or a frequency, then use that value to adjust a digital
> potentiometer like these http://www.maxim-ic.com/products/digi_pot/
> Unfortunately, it appears that 10Kohm is the smallest end-to-end value and
> 64 steps is the smallest increment, so the smallest change I can affect is
> 156 ohms. That doesn't even consider that there is a minimum series "wiper"
> resistance of 100ohms.
> By paralleling the digi-pot with a fixed resistor, I can get a piece of the
> range. 10K + 100 = 99.01 ohms, which is good. but minimum is 256 + 100 =
> 71.91, giving me a workable range of roughly the 1/4 tank.
> Anyway, does anyone have any ideas or suggestions for this problem?
> Thanks!
> Robert/Sluggy!
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