How to monitor an actuator's feedback line from a microcontroller?

[FvM]

How do you come to the conclusion that the aux contacts need to be operated with 24V, involving all the voltage divider stuff etc? These are separate micro switches, they can work with 3.3 V logic as well. Particularly I don't see a reason for optical isolation when the actuator circuit is operated at the common logic ground.

If you expect untrained staff confusing the device wiring, you can provide pull-up and series input resistors with 24V rating.

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As for the actuator drivers, there's no indication that the open circuit voltage is lower than 24V supply, so using driver transistors as shown in your schematic seems appropriate.

 

[Skyland]

If you expect untrained staff confusing the device wiring, you can provide pull-up and series input resistors with 24V rating.

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Why would you need a resistor in series if it's an input to the MCU?

 

[FvM]

In case someone shorts the input line to 24V supply.

 

[Skyland]

Is the 1K resistor at the gate of the low side switch necessary? I've put it there to limit the current but thinking about it the MCU current is in the uA range

 

[FvM]

uC pins have clamp diodes to Vdd with e.g. 10 mA current rating that start to conduct when Add is exceeded by 0.5 V. For higher currents, external clamping circuits are required.

The 1k gate resistor is not absolutely required, but limits the current peak during switching.