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I've got the following circuit going:

A Vishay opto-isolator (CNY74-4) that takes input from buttons that work on 24V, and outputs to microcontroller pins (an Olimex ESP32-PoE-ISO in my case).

A ULN2803 darlington array connected to the microcontroller, +24V and GND, driving LEDs.

Initially I had designed the circuit so that the 24V of the buttons had its own separated GND. But to use the ULN2803, I need to connect the GND of the microcontroller to the GND of the 24V power supply, or it won't work.

This entire setup works perfectly, but I'm wondering if I should also put an opto-isolator between the microcontroller and the ULN2803. It might be overkill, but then the 24V power supply is completely separated electrically from the microcontroller.

I discovered the Vishay ILQ30, an opto-isolator with darlington output. It could take care of this in one DIP. Or the Toshiba TLP627-4, that one is in my KiCad library :)Image of the schematic

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    \$\begingroup\$ A Vishay opto-isolator ... that takes input from buttons OK, to describe circuits we use a schematic please include one. \$\endgroup\$ Commented Nov 7, 2019 at 14:02
  • \$\begingroup\$ The schematic is divided over multiple sheets in KiCad - I have time later tonight to draw a clear one for this question and include it. \$\endgroup\$ Commented Nov 7, 2019 at 14:21
  • \$\begingroup\$ Try the edit button below the question and click the schematic button. Pretty easy to use. :) \$\endgroup\$ Commented Nov 7, 2019 at 14:42
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    \$\begingroup\$ There is no environmental need defined in your question for an opto. isolator. (overkill) \$\endgroup\$ Commented Nov 7, 2019 at 14:55
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    \$\begingroup\$ To add to Tony's comment - what are you attempting to protect against that would require the isolator? ESD? PSU noise? Spikes from motor drive? \$\endgroup\$ Commented Nov 7, 2019 at 15:50

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