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I want to use a raspberry pi to pick up some 24v DC inputs. I would ideally like to use an off the shelf module to add this functionality to my Pi (v3 model B).

I have come across this range of relay cards - http://denkovi.com/relay-cards-24v which feature circuits like this:

enter image description here

These are obviously intended for allowing the Raspberry Pi to drive 24V outputs. But could I could I use my 24V input as the Input and then have +5V on C and connect NO to the Raspberry Pi terminal?

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    Remember the Pi GPIO must not be exposed to more than 3V3. – joan Apr 22 '17 at 20:07
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It would be simpler just to use a voltage divider to bring the 24v down to 3.3v for the Raspberry Pi or safer still use an optocoupler such as the 4N35 which is what I would use personally. Example circuits are on the 4N35 datasheet which is readily available.

schematic

simulate this circuit – Schematic created using CircuitLab

4N35 Pinout

4N35 Pinout

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  • I can't seem to find any off the shelf modules which break out the Pi GPIO with opto-isolators – George Edwards Apr 22 '17 at 20:20
  • No you'd need to add the 2 resistors yourself, surely simple enough to do ? – Bra1n Apr 22 '17 at 20:29

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