routercnc_MK3

[irving2008]

The point I was making is that if your BOB has optoisolated inputs you can run these directly at 24v with 5kV isolation and all the noise immunity you need and saves all the hassle, adding an optoisolated relay doesn't 'make it better' just less reliable. Noise immunity is only an issue with non-isolated 5v BOB inputs.

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Incidentally, if that is the circuit on that board then it has a potential noise immunity issue of its own unless used in a 'permanently energised' arrangement. With the diode not energised, the base of the output transistor, say Q1, is floating. Depending on the gain of Q1 a sufficiently large spike could briefly turn the transistor on and energise the relay. It should have a pull-down from the base to ground to prevent charge build-up on the base. A moot point and unlikely but not impossible.