As mentioned before, the following relay GPIO card worked great for me: gpio 4 is relay 1 gpio 22 is relay 2 gpio 6 is relay 3 gpio 26 is relay 4 others too have mentioned that the relay controller mounting hardware doesn't quite fit the board (leaves small gaps, see attached pictures), but it still works. Another thing I want to mention is that you need to know the height of the heatsink you have on the PI processor. . If the heatsink is too high, it will prevent the relay controller from installing properly and may cause equipment damage if the heatsink and relay controller come into contact. I learned it the hard way.
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