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Queens, New York
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Btw, it is kinda hard to see the information in the pictures even when double clicked. Their blurry
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To  me it appears it is a dual outlet... in my mind the diagram indicates that if the horn is connected to either 85 or 86 and the Arduino to 87a (center prong) then when the relay receives the 5 volts from the Arduino it will pull the contact closed to complete the circuit for the coil on either 85 or 86. Just when I think I see what is going on I start looking at it from a different viewpoint ... I think I will splurge a few bucks on a couple of optoisolators that way I will know for a fact that I am keeping the 5v side completely away from the 12v side so I can afford a few screw ups and maybe learn something in the process. I've been doing ok with the Arduino sketches that lead me through step-by-step like a recipe but venturing into something like this is all new to me. Thank you guys for being so patient.
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Sorry about the picture quality... my daughters took my AA batteries out of the good camera (without telling me of course lol) so I had to use my cell phone.
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The coil is what changes where the output is going. Wire it the same way I showed in my crudely made drawing. The output pin from the arduino is going to change the output from the relay to normally closed => normally open when a current is applied to the coil. The horn does NOT get wired to the coil contacts.

Can someone else post a video or better picture then mine that is wired with something like an LED.

87a is NC (not used)
87 is NO (horn)
30 is common (12v power supply for horn)
85 (ARD)
86 (ground)
« Last Edit: November 18, 2012, 01:46:17 am by HazardsMind » Logged

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Your relay:

            ___ (either 87 or 87a check)

(86) |   ___   |(85)

              |(30)

Hope this helps you understand your relay connections.
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           87 |

| 86     87a|      85 |

           30 |

87a (Center Prong) Reads 2 1/2 ohms with DMM.


       
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Thanks Hazard, I found this YouTube video -


It actually matches my relay exactly and makes me see your previous explanation... it totally clicks now (pun intended) :-) Do I connect a ground wire from ARD AND the Horn to neg on the coil?
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Yes
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Well guys I put some juice into it.... and.... I don't think 5 volts is going to drive the relay... I need a different relay or transistor. I put a 2N3904 in the equation and nothing. I did test the relay by putting the 12v PS to the coil terminals and it's clicking so it's a good relay. Now with my completely non-existent electrical background I need to figure out exactly which parts I need. The voltage on the relay says both the NO and the NC are 14 volts. Do they make relays that one is like 5 volts and the other is 12?
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It might take 14v to trigger the relay.
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The voltage reading I get from my ATX PS wires indicates 12.7 volts on the DMM. I just found in my POP (pile of parts) a 2N4401. I "think" this may be enough to trigger the relay if I can figure out how to wire it. Looking at the specs for the 4401 it should handle up to 600ma from the ARD (which I've read it only takes about 200ma to trigger a relay) and the 4401 can handle up to 40v out which should definitely be enough power. Time to start probing with the DMM again ....
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