Latest picture and update on my real 727 engine gauges working

[LH784]

Hi Rob, hi all,

could you tell us which two pins you finally addressed in the N1, N2 and EGT gauges ? You had supplied some of the original documentation. Going throu the old thread however I was not able to finally figure out which two pins (input, GND) were used.
Thanks a lot,
Florian

[arnolde]

The APU % indicator pictured uses 3 phase synchronous AC motor with permanent magnets rotor and unlike synchro uses only three wires.
Operation is achieved by spinning the motor at a speed proportional to APU speed. The airgap magnetic coupling causes the needle to deflect in proportion to the rotor RPM.
To drive this and similar RPM gauges you need to supply 3 sinusoidal signals shifted 120 degrees to each other somewhere in the region of 12V or possibly more.

Could this be done with a 3-phase motor driver IC like this one?
http://www.freescale.com/files/micro...et/MC3PHAC.pdf