fuel gauge

[kinarfi]

Mike, I seem to be getting stuck at the integrator and the rectifier. I'm not seeing a change of voltage as the capacitance changes. Is R 7 47K or 220K? The down load has 47 K and the thumbnail has 220K Just noticed. I add 22nf to the probe for testing and I get the frequency change but can't see the voltage change, still working on it. Will post info tomorrow.
Thanks again,
Kinarfi

 

[kinarfi]

First, I pulled the meter out and measured it, Red to Black = 305.4 Ω, Red to White(to tank wire) = 111.3Ω, Blank to White = 194.3Ω. The voltage out of the meter appears to be a voltage divider.
The attached is the schematic of what worked and after adjustments, the 2nd number by the pots is their setting.
In practice the "true opamp integrator" produced a 10 volt square wave, so I went back to an RC integrator.
Another fun little project,
Thanks for the help,
Kinarfi