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Member • Oct 17, 2008
Member • Oct 17, 2008
Member • Oct 27, 2008
Typical fuel tank sending units have a resistance of 0 to 10 ohms in the full position and 90 to 240 ohms in the empty positionThis design doesn't take care of the high resistance inaccuracy of the Sending unit. I assumed 0 Ohm and 240 Ohm.
Member • Oct 27, 2008
Member • Oct 28, 2008
What I meant to say was that the sending units vary with manufacturer and a particular unit could have resistance of 10 to 90, or 0 to 240, or anything in betweenAh Ok ! Now I understand the meaning of the resistance variation.
Could I stick a voltage divider or zener circuit ahead of the 240 ohm series resistor to cut down the voltage at Vin?Of course you can. It is also a good idea considering the fact that Battery is not a stable voltage. As you said it would also reduce the current through the sending unit.
What is an appropriate range of values when selecting R1, R2 (and R3)R3 would have to be same as the resistance of the sending unit. And as per the formula R3=R1*R2/(R1+R2). Since you want a gain of 2, R2=2R1. You can calculate accordingly.
considering the extremely low load on VoutThat should normally be no issue. In any case you can put a 10k to GND at Vout to act as a load and the circuit would still work.