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I need to control a 12 volt 5amp device from one of the pins on a Arduino BT.
Since the board has a max out of 5 volts I need some type of affordable relay.

I have tried Googling 5v 12v relay, but not have much luck.
Can someone point me in the right direction.

Thanks 
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I read something about that.
Can you explain more about a simple transistor switch or
point me towards some information.

Thanks for the fast response

I found this:
http://www.robotroom.com/Pilot-Switch-2.html
« Last Edit: September 29, 2011, 09:30:38 am by frenchsquared » Logged

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Here is a typical 12vdc automotive type relay. As the coil requires 12vdc to activate you will need to have a small transistor switching it on and off via a arduino output pin.

http://www.allelectronics.com/make-a-store/item/RLY-351/12V-SPDT-30-AMP-AUTOMOTIVE-RELAY/1.html
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Unfortunately, I'm not sure I can read that schematic.
I know I have a lot to learn.

Here is what I have pieced together. It is working, but that doesn't mean it is not correct.

1 npt Transistor MPS2222A
1 1k ohm resistor

5 volts running to the gold stripe side of the 1k resistor. The brown side of the resistor is then wired
to the center post of the transistor. That should then power the transistor. I then have a ground wire
going to the left side of the Transistor. And finally another wire coming of the right side of the
transistor. This wire goes to the ground side of the relay. The power side of the relay is full time 12 volts.

When the Transistor is powered, the ground is completed and the relay triggers.
When power is removed from the transistor the relay opens and breaks power.

It is working nicely.

Looking at the diagram you posted I think the only thing I am missing is the diode.
Where would this diode go. I think it goes from the 12 volt side of the relay to
the ground side coming off of the transistor.
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Quote
Where would this diode go. I think it goes from the 12 volt side of the relay to
the ground side coming off of the transistor.

Best placement for the diode is right across the two coil terminals on the relay.

Lefty
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Hi, While I think it's best to do this yourself and learn stuff, if you're in a hurry and don't want to build the circuitry, there are many relay boards on Ebay, Futurlec, and my site: http://goo.gl/8ZEQ8     (many of the boards linked there include the schematic diagrams, for reference. They look like they stole the design from KE7GKP..)

DISCLAIMER: Mentioned stuff from my own shop...! 
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I need to control a 12 volt 5amp device from one of the pins on a Arduino BT.
Since the board has a max out of 5 volts I need some type of affordable relay.

Not necessarily, you could use a logic-level power mosfet instead:

- source terminal to Arduino ground and the -ve side of your 12v supply
- gate terminal to the Arduino pin through a 100 ohm resistor
- drain terminal to the -ve side of your 12v load
- +ve side of your 12v load to +12v

If the load is very inductive (e.g. motor or solenoid), add a 5A diode in parallel with the load (anode to mosfet drain, cathode to +12v).
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