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I have a fuel level sender in a tank that ranges from 18 - 180 ohms (standard euro range) and is connected to a standard gauge that measures the resistance. I'd like to connect it to a micro-controller to feed my on-board data streams.

Removing the gauge I can connect the sender to (say) an Arduino quite trivially using a simple voltage divider circuit, but how can I connect it to the gauge and Arduino simultaneously whilst keeping the resistance (as perceived by the gauge ) as 18 - 180 ohms

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  • \$\begingroup\$ Presumably there is some voltage drop across the resistance as the meter reading changes. Just determine the mapping from voltage to meter reading and you're all set. The Arduino inputs are high impedance, so just measuring the voltage should not affect the meter reading. \$\endgroup\$ – crj11 Mar 20 '18 at 13:23
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The fuel gauge and sender form a simple voltage divider network, with the gauge resistance fixed, and the sender being proportional to fuel level. As the sender resistance changes the current through the gauge changes and the needle moves. You can calculate the sender resistance in situ by just measuring the voltage across the sender directly. I can't remember the exact numbers, but the gauges are usually 200 ohms or something, so the voltage range is between 1-6 volts (for a 12V supply).

Also note that changes in the battery voltage will affect the measurement, so you might want to measure this as well if you need good accuracy (also note most factory fitted fuel senders are horribly inaccurate).

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  • \$\begingroup\$ In such a scenario, adding an Arduino to an existing sender/gauge combo works well only if the gauge is present to provide a sensing current to the sender. In a 12V system, some overvoltage protection diodes added to the 5V Arduino would be prudent. \$\endgroup\$ – glen_geek Mar 20 '18 at 13:34

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