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France
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Hello smiley

So I would like to buy this 12V relay board and connect it to the Arduino Mega (with two, daisy chained 74HC595 shift registers):


Can someone simply please take a look at these schematics, and tell me what are those two 5V and two GND pins for? I asked Sainsmart about it but they told me to look the schematic..which I already did.

You should have guessed, I'm beginner and can't really read schematics yet, all I know is that I'm confused because it's written "low level INPUT", which make me think that I must supply 5VDC to those pins, in addition of the 12VDC to the screw connectors...Doesn't make sense. Or does it?

Thanks!
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I am sorry, there is nothing wrong with your learning curve, but these guys are jerks and you should not support their hardware ventures.  These "schematics" are *not* schematics.  These as PCB files.  It says their PCB files.  If this was a single layer project, I might forgive it, but no.

Anyhow, the double pins are *probably* for each bank of relays.  Top pin is for the even number and bottom pin is for the odd number.  To trigger relay "4", you *probably* need to power the top 5v and top Gnd and pin 4.  If you hook up the power to the bottom 5v/Gnd and pin 4 it *probably* will not pull the relay.  I can't say, because I do not want to study from a Multilayer PCB diagram in PDF.

I apologize again, these guys are really annoying.
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Dubuque, Iowa, USA
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The two 5V pins and two GND pins are connected. They could reduce those pin blocks to 2x9 pins, but pin headers come in 2x20 configuration as standard and they'd just be throwing the extra pins away.
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wow, just look at all those optoisolaters on that board :O

Seriously, a good old fashioned diode simply no longer good enough to protect your arduino from voltage spikes??! - and if anyone think's it's not good enough, I once managed to Restart my Arduino board from messing with a relay (switching it on and off, with it's terminals connected to the board, purely accidentally, but nothing broke, Atmel did a splendid job with their atmega chips smiley
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Typically the +5vdc and ground input is to supply the power needed to operate the input stages of the optoisolators and as such should be wired to the arduino ground and 5v pin. Then you can wire the relay channel input pins to arduino output pins and most likely a digitalWrite LOW will activate the relay and a digitalWrite HIGH will turn the relay off. The 2 pin connector to the right is for an independent +12vdc (and ground) power source to operate the optoisolators output stages and the relay coil circuits.

 The fact that you want to drive this board with a shift register will complicate it some, but certainly possible. Most likely whatever you wire to the channel input pins will probably be required to be able sink 20ma of current in the LOW state, which many shift registers cannot do without additional transistor output components. Are you sure you don't have enough pins on a mega board to operate these relays directly? You do know that you can use the 16 analog input pins as digital output pins if you wish?

Lefty
« Last Edit: September 28, 2012, 07:44:06 am by retrolefty » Logged

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Quote
what are those two 5V and two GND pins for?

The board takes a 12v input and produces a 5v output, for the optocouplers: the relays / drivers / leds run off the 12v source.

The 5v pins are routed out, to potentially power other peripherals.

The inputs are "isolated" by the opto-couplers (active low) and you should have no problem driving them with a shift register: the "isolation" however shares the same 5v, according to the schematic.

Quote
These "schematics" are *not* schematics.  These as PCB files.

One of the files is a schematic for the board.
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France
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Thank you all smiley

spcomputing, I agree with you about the multilayer pcb in a pdf file, in which you can't select a layer anyway so what's the point! I tried to convert that pdf into a pcb file, but I can't find anything about it (tried "pstoedit" but no luck). But Chagrin is right, both 5v pins are connected together, and same for the GND pins.

Retrolefty I agree with dhenry, from what I understand the 12VDC go into the LM2576 which then distribute 5VDC to opto isolators, then to those 5V pins. I just wasn't sure about myself so I asked..I always ask when in doubt! And yes, I knew about converting the 16 analog to digital, we already discussed that in another topic of myself, I want to save pins because my project will be quite big in the future! Of course I will first try to connect some relays directly to the arduino, and once I get this working, only then I will try introduce the shift registers (buyed 5 of them so I'm ready to sacrifice some if things go bad smiley).

About the opto isolator, I've read that they are model 817C, and require something like 3mA each. Again, I'm not sure, but I guess I will just have to try and see. I just hope I will not fry the arduino smiley-razz.

I think I'm now ready to buy this board and have lot of fun - or problems - with it!

Thanks again everyone, appreciated.
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Quote
what are those two 5V and two GND pins for?

The board takes a 12v input and produces a 5v output, for the optocouplers: the relays / drivers / leds run off the 12v source.

The 5v pins are routed out, to potentially power other peripherals.

The inputs are "isolated" by the opto-couplers (active low) and you should have no problem driving them with a shift register: the "isolation" however shares the same 5v, according to the schematic.

Quote
These "schematics" are *not* schematics.  These as PCB files.

One of the files is a schematic for the board.

Good catch. I didn't feel like downloading the compressed file to actually looking for a schematic and as I said I was describing a 'typical' Asian relay board. Never saw one before that included a built in regulator or DC to DC converter. I myself would probably not build or buy a relay that used opto-isolators as that seems like redundant isolation in my way of thinking. I like optoisolators for driving higher voltage transistor switching boards, but again don't see a real advantage to having double isolation with standard relays and optos.


Lefty
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