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).
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.