Arduino connection to "Keyes" multi channel relay module (yes, the red one)

Using Arduino Motors, Mechanics, Power and CNC
1

Hi everyone and thanks in advance!

I'm having trouble understanding the connection of a external power supply to this specific relay shield:

This is a really useful module, but I'm not able to find a lot of documentation about it, I mean, I've readed a lot of posts related to relay shields and Arduino connection, but they are for different modules, for example this one:

There is a different way of connecting this one, and I'm not understanding it very well...

For example, you can check this link and the documentation is awesome! but my relay shield doesn't have this kind of connections, instead, I've found this documentation (it works the same way besides it is for a 8 channel module) but I'm not understanding how I can use opto-isolation...

The connections that I've made can be seen in the "wiring" attachment (sorry guys, really, I hope your eyes will still able to work after seeing that monstrosity :o).

The GND and VCC are connected to an external power supply (5V-1A DC). The IN's from 1 to 4 are conected to arduino pins 2 to 5, and I've removed the jumper between COM and GND, and connected arduino GND to COM...

The question is: can we say the relay module is, then, full isolated?

Thanks a lot, and sorry if it is a stupid question. :frowning:

4_channel_relay.png
4_channel_relay.png842×826 438 KB

4_channel_relay_blue.png
4_channel_relay_blue.png634×504 387 KB

wiring.png

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If the board is designed correctly then probably yes, the Arduino should be isolated from the relay contacts.

The questions I have is what is "gnd" and what is "com". I assume (and it's just an assumption) that "gnd" is the return line for the Vcc power supply which supplies the relay coils and is only one the "outside" of the optoisolators and "com" is the return line for the command signals and is only on the "safe" side of the optoisolators.

3

sdturner:
If the board is designed correctly then probably yes, the Arduino should be isolated from the relay contacts.

Yes, I Think that way too...

sdturner:
The questions I have is what is "gnd" and what is "com". I assume (and it's just an assumption) that "gnd" is the return line for the Vcc power supply which supplies the relay coils and is only one the "outside" of the optoisolators and "com" is the return line for the command signals and is only on the "safe" side of the optoisolators.

It could be, if I disconnect the "com", then the signals can't control the relays, so, It must be connected for it to work. I think you're right.

Thanks for your response and your time!