Fuel Quantity Gauges

707 fuel gauge

Fuel Quantity Gauge 6x

The fuel quantity gauges on the 707 are a bit tricky to convert to stepper motors since the have two needles very close together.  The main indicator needle turns less than 315° (which is the limit of the Juken X27 motor) and thus does not require a zero position sensor as its has an internal stop.  The second needle has a continuous rotation which requires a position sensor (otherwise the hardware does not “know” the current position of the motor). This is usually done with a thin electric contact wire, IR opto sensor, or Hall-effect sensor. I decided for the IR opto sensor HOA2001 (no longer in production).

System description

An individual fuel quantity indicator for each tank is calibrated to read kilograms of fuel in the tank. A total fuel quantity indicator is calibrated to read total kilograms of fuel remaining in all the fuel tanks. A single push-to-test switch marked PUSH TO TEST GAUGES is on the FIE’s lower panel, and when pushed will drive the indicators toward zero . When the switch is released, the needles will return to their original reading. The power is 115V AC through P4, FUEL QUANTITY, LEFT , RIGHT, CENTER.


For more information on the fuel system click here.