new here need some advice one wiring a duinotech 4 relay board with external power supply and separate 5v control ? 5 v is coming from a grbl cnc control to turn on a router
Commonly in these opto-coupled relay modules you connect arduino pins to the inputs, and Arduino 5V to the opto coupler common. However from the printing this seems to use an opto coupler common at ground, not +5V. So I think you connect arduino gnd to "COM", and remove the link (though you'd need to check
how its actually wired up to be sure). Buzzing it out with a multimeter is the way to
check.
Remove the link and provide separate isolated 5V power to the left two pins (these power the relay circuitry after the opto coupler).
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