Help with simple led wiring

  • Thread starter rougeqc21
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Main Question or Discussion Point

Alright I need help. I am not electrically inclined so figure this is the best place I could have come. I'll make this as simple as possible.

I have:
1 Red 5 mm LED with specs 2.6V - 28mA * 10mcd
1 Green 5mm LED with specs 2.1VDC - 25mA - 6.3mcd
9V battery as source

What I need.

Need to wire this so that the green led is constant on and when a switch is depressed the green turns off and red turns on then if the switch is released back to green.

radioshack.com/product/index.jsp?productId=2049718&cp=&kw=lever+switch&parentPage=search

that is the switch I have.

Thanks so much for your help!
 

Answers and Replies

Redbelly98
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I have attached a circuit that should do what you want.
The 330 ohm resistors will give about 20 mA through each LED.
 

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Redbelly98
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rougeqc21, I should probably ask by what means you would be making connections in your circuit? I.e., soldering, or using wires with alligator clips (available at Radio Shack), or a solderless breadboard, or other?

Feel free to post if you have more questions.
 
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Thanks for the help redbelly.

I will be soldering it all myself, that at least i am proficient at haha from hobby related endeavors. Would that switch I had the link to work? I hooked pos and neg from the 9V and it seemed like it was just shorting the battery out (it was getting very hot)
 
Redbelly98
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If you hooked the switch up directly to the battery, then yes you were shorting it out.

I can't find a wiring diagram for the switch at Radio Shack (not surprisingly), so I can't answer for certain that it will work. But it is listed as a spdt 3-lead switch. So one lead (probably the center one) is always connected to one or the other of the other 2 leads. That lead is what gets connected to the battery. As for rest of the connections, see the circuit diagram I posted earlier.

I'll suggest getting some wires with alligator clips just so you can verify and debug your circuit before you start soldering things. You can waste a lot of time desoldering and resoldering if things are not connected correctly. I saw the clip wires at my local Radio Shack earlier today, they come in a package of 10 and might cost $5 or at most $10.

As a start, connect 1 LED and resistor to the battery leads to satisfy yourself that things will work. This will also tell you the polarity of the LED (which wire is +).
 
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Reminder:
By using 330ohm resistor, it rates to 27mA (not 20mA) for 9VDC. It should be 360ohm for both (25mA and 28mA)
 
Redbelly98
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But the resistor does not have 9V across it, it has
(9V - Vled)
or 6.4V to 6.9V, depending on which LED is connected (2.6V for the red one, 2.1 V for the green).
This gives 19 mA or 21 mA, or (as I said) close to 20 mA in either case.

The resistor and LED are in series, in case that is what caused your confusion.
 

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