Schema for 12V relay board ?

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michael_l
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Schema for 12V relay board ?

Postby michael_l » Sat Dec 31, 2016 2:50 pm

Anybody happen to have schematic for this particular board with IN, VCC and GND and optocoupler ?

http://www.ebay.com/itm/12V-1-Channel-R ... Sw7s5Xgzcv

Would like to know how VCC and IN are separated - is there any risk to have VCC leaked into IN pin. Thanks.

fredbox
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Re: Schema for 12V relay board ?

Postby fredbox » Sat Dec 31, 2016 4:27 pm

A search for "Arduino Relay Schematic" in Google images should find it. Chances are, it is this one.
If not, there are may more examples there.

michael_l
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Re: Schema for 12V relay board ?

Postby michael_l » Sat Dec 31, 2016 4:39 pm

Thanks, I'll check that.

I'm worrying if I put +12V in VCC and +5 IN from STM that I got no isolation between the relay and the microcontroller.

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Pito
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Re: Schema for 12V relay board ?

Postby Pito » Sat Dec 31, 2016 5:38 pm

From the picture it seems the Input IN goes via 1k and the optocoupler's diode to GND - that is the "isolation".
The VCC will be 12V, the optocoupler's transistor drives the external transistor which then drives the 12V relay against VCC to GND.

GND is common to 12V VCC and IN, therefore no galvanic isolation between 12V and IN. You would need a separate pin called "IN_GND" (for the optocoupler's diode return) in order to get full galvanic isolation of the 12V VCC from an MCU connected to IN..
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michael_l
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Re: Schema for 12V relay board ?

Postby michael_l » Sat Dec 31, 2016 6:21 pm

Thanks for the explanation. It seems my board seems to be a bit different.

IN is wired straigth into optocouplers kathode and VCC goes through 222 resistor into anode.

Image

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Pito
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Re: Schema for 12V relay board ?

Postby Pito » Sat Dec 31, 2016 6:56 pm

Then it is even worse :cry:
The optocoupler there has no specific reason to exist then.. :)
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michael_l
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Re: Schema for 12V relay board ?

Postby michael_l » Sat Dec 31, 2016 7:05 pm

Hmm.. Yeah it doesn't make sense. I'll have to recheck :)

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Pito
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Re: Schema for 12V relay board ?

Postby Pito » Sat Dec 31, 2016 7:24 pm

This is how it should be wired to make us happy (LED and other jelly beans exclusive):
Ardu relay.JPG
Ardu relay.JPG (19.91 KiB) Viewed 211 times

The IN and IN_GND headers could be called IN+ and IN- as well..
R2 value such it switches the relay "on" reliably (1k-10k).
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michael_l
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Re: Schema for 12V relay board ?

Postby michael_l » Sat Dec 31, 2016 9:29 pm

Pito wrote:This is how it should be wired to make us happy (LED and other jelly beans exclusive):
Ardu relay.JPG

The IN and IN_GND headers could be called IN+ and IN- as well..
R2 value such it switches the relay "on" reliably (1k-10k).


Thanks!

This is the best schema I've seen so far and fully galvanic separated. From the picture you can see the traces.

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Pito
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Re: Schema for 12V relay board ?

Postby Pito » Sat Dec 31, 2016 9:33 pm

But the schematics of mine is not the schematics of your board..
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