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SYNCHROS "SELSYNS" as Input Devices  

Peter Elsler
Active Member
Joined: 3 months ago
Posts: 19
Topic starter  

SYNCHROS "SELSYNS" as Input Devices - In this case, the SYNCHROS or “SELSYNS” are used measuring the exact position of these SYNCHROS, moved by mechanical movement inputs, such as done by the SET ALTITUDE INDICATOR.

In my example of the shown SET ALTITUDE INDICATOR, there are the following devices:



Rotor:      3 Phases  11.8 V       400 Hz  -  4 wires   black - red – blue - yellow

  Stator:     2 Phases  26 V          400 Hz  -  3 wires   black/white - blue/white - yellow/white



Rotor:      1 Phase  23.5 V         400 Hz  -  2 wires   black/white- red/ white

  Stator:     3 Phases  11.8 V       400 Hz  -  3 wires   black – yellow - blue


Most probably, the Differential Resolver is used to move a second, identical Set Altitude Indicator on the co-pilots side to identical settings.

As shown in literature, 400 cycles are used in aeronautics and naval industry to reduce the size of electronic parts and diameter in cabling to reduce weight. Therefore 60 Hz signals cannot be used to drive these instruments, otherwise the small coils would burn because of current increase.


I would like to decode the synchro positions by Arduino, to obtain a numerical output.

If possible, I would like to move the instrument on the co-pilots side to identical settings, too.


Any help would be appreciated.

In advance, many thanks.



SET ALT Indicator 01
SET ALT Indicator 02
SET ALT Indicator 03
SET ALT Indicator 04
SET ALT Indicator 05



Prominent Member
Joined: 2 years ago
Posts: 818

For those like me who don't know anything about a selsyn.


Is this what the question wants answered?

Turn down the pc volume before running the video if you suffer from tinnitus!!


This post was modified 3 months ago 2 times by robotBuilder

Peter Elsler
Active Member
Joined: 3 months ago
Posts: 19
Topic starter  

Many thanks, robotBuilder.

This are great links and I will carefully analyze them. Some videos, I remember that I have just seen on the internet. By the sound they make, it seems that they use sound amplyfiers to give the 400 Hz sinus curves for driving the 3 stator coils.

I prefer another approach: I want to use PWM square waves from the arduino to create magnetic fields in the coils, one permanent magnetic field in the rotor and 3 changeing magnetic fields in the stator coils, depending on the position of the indicator needle. - This is for the use of synchros as output devices.

Using them as input device, I think to use permanent PWM-square waves on the rotor and analyze the 3 resulting waves from each coil, generated by the magnetic field, by the arduino.

For both problems, I am searching primarily for suitable arduino codes.

Many thanks for your post.