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Building in isolation.

20 Oct

In regards to the post regarding galvanic separation the other day, when I build things, this is my go to circuit…

So, what this is here, it is a simple opto-isolator running on a 5v input line; when it gets power from the 5v, it goes high, when it doesn’t it goes low. And in that process it turns on, or off whatever is attached.

On the line between the ground pin on the opto-isolator (cathode for the technical minded) and the ground plane, I will sometimes put in an LED (like in this diagramme) for two reasons. One is to say if the opto-isolator is turned working when there’s nothing attached to the signal line, and the other is to tell me if it’s off when attaching something. Also, it’s an easy way to put in a bit of user feedback so when the LED is flashing, it’s doing without having to tie up another pin on a micro-controller if that’s the route that has been followed.

So here, simple circuit, simple parts list…

  • R1 : 220 ohm resistor. You may need to calculate a different value depending on what your input voltage is, but this here is for 5v.
  • PC817 opto-isolator, these I find to offer the best balance of speed vs lowest resistance to trigger off a camera, different ones may be too slow or may not trigger a camera’s remote shutter line.
  • LED : this here is just a red one, if you decide to use another colour, then you may have to change R1 to accommodate.
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