Digital servos & the Wren54??
Further to the above.....
Hello Marc,
You should put it in the hall sensor lead, not in the fadec lead.
This isn't RFI, nothing to worry about, and the relative position of all
items inside the plane doesn't matter, because it isn't a radiated
interference. What happens is that the digital servos draw a lot of current
in very small pulses. Due at the resistence of the wires, switch,
batteries,.. this high power pulses cause that the supply voltage of the
FADEC decrease below a 4.5V in form of pulses that go directly to the
magnetic sensor circuit, and this one counts the pulses from the servos as
pulses from the engine. Installing a capacitor in the sensor line, it
filters the supply of the hall sensor and cures the problem. This problem
apppears with the rotor at rest, because automatic gain control of the
sensor is at maximum gain, when the engine turn the pulses from the magnet
are many times stronguer and the noise from the servos is ignored.
The Fadec itself can work with voltages as low as 3V, so this isn't a issue
for the microcontroller or the temperature sensor.
If you want to be sure that is a power issue, test with a 6V battery or
power the fadec with a separate battery. You will see that all is OK. If it
is radiated, the problem still will be here.
Regards,
Gaspar