Hobb7t:
I just found out a documentation for my relay, saying nothing more from what i already knew...
The very first line of that document is a big fat lie.
These 16-relay boards do have opto couplers, but they are just ornamental.
No opto isolation with these boards. Only the 8-channel version has this option.
You can find the schematic diagram on the Sainsmart website.
The next incorrect information on that document is power draw.
The relay coils draw 75-80mA each, and the input/drive pins need a sink current of 2mA.
The 20mA stated seems to be pulled out of a hat.
There are two versions of this board.
The one without 12>5volt buck converter is shown (power parts missing).
That means this board needs a 5volt/1.25A (minimum) supply.
Leo..