12V 16 relay board powering

Hi all,

First of all I’m a beginner of electric but something is not clear to me.
I bought 16 12V relay board with optocouplers. If I connect the arduino +5v GND and IO pins to the board I just wonder the relay board powering the arduino itself. I see the 5v regulator on the relay board, but normally it should power only the optocoupler collector emitter site. I thing between the arduino power and on board 5v regulator missing a DCDC 5v to 5v isolator.
Can this board make any noise problem or it is perfect?

Thank You

16 RELAY.pdf (491 KB)

16 relay 2.pdf (55.1 KB)

Can this board make any noise problem or it is perfect?

Sadly, it’s far from perfect. As you’ve identified, there is no isolation provided on it’s 5V circuit. This renders the opto-isolators to be useless.

Labeling problem - ULN2083 should be ULN2803.

Schematic shows relay contact COM at terminal 1, advertised as at terminal 2. (other relay modules use terminal 2).

Cannot identify NO and NC contacts on schematic.

May operate OK without isolation, but once connected, the Arduino’s 5V short-circuit protection is lost and 3 AMPS @ 5V is available (far too high).

I’d stay away from this board.

I just wonder the relay board powering the arduino itself.

That doesn’t make sense. Do you mean a common 12v power supply powering both the arduino and the relay board?

Thank You for answer,

Yes common 12v power for both the relay and arduino (arduino get 5v regulated). I use one etherenet shield and 4 relay boards drive by arduino mega. Ethernet using 6pins, relay boards using 64 pins. There are everywhere this relay board on the market. Newer thought has this basic mistake. Doeas anybody has Idea how to hack it?

Does anybody has Idea how to hack it?

After PCB modification, the interface to Arduino would be as follows (do not use GND connection):

Thank You Dlloyd,

Yes arduino GND not connect. Please look at my image may be it is "easier" to hack. SMD resistors are very small to solder or cut isolation around.

only PR1, PR2, PR4, PR7 resistor blocks for opto leds needs arduino 5V power. black line = isolate green = top solder wire yellow bottom solder wires to pins

Easier solution:

I just realized that the relays are powered by 12V (wonder why the large 3A 5V regulator is required?). Anyways, just remove IC2 (LM2576) and optionally remove C2. That's it.

NOTE: On JP2, you will need to use the GND to Arduino for the opto-transistors - there won't be opto-isolation but the relay board should operate OK.

I decided to left it in original state.