# how do you wire led's in a line circut with one on off switch. very new to this.?

i want to make a sign for a play that can be turned off for other scenes. I want to wire led's together in one circuit with one power source. (how much power and what type would I need?)

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collard419 years ago
Ok, now i have time.
i have composed a circuit, this has nine LEDs, three sets of series LEDs in parallel with one another.
it is only necessary to have one Resistor because you are not going to control them independently.

With the resistor value i have put there the LEDs draw about 20mA (a bit more actually) i have guessed that the forward voltage drop of the LEDs is about 2V.
this gives;
V/I=R
12-2-2-2/0.02=300
6/0.02=300
I haven't come across a 300 Ohms resistor so I used 270 Ohms.
2 years ago

"it is only necessary to have one Resistor"

sadly this is horribly wrong. You need 3 resistors - one for each set or string. Otherwise one set [with a lower total Vf] can start grabbing current and burn out.

bluefly1215 (author)  collard418 years ago
Thanks everyone, I appreciate the info. Laptop crashed had to get it fixed before I could get back on.
pie_lover1239 years ago
wire a parallel circuit. If you have problems figuring out a resistor, there is an led ohm calculator online. It will show you how to wire them in parallel, also. series works the same, but be careful, the first on the positive side will be the brightest.
Mighty Mackinac9 years ago
Shinta sums it up nicely...it is a pleasure to know that someone out there knows their stuff... It depends on how many leds you need and how much power you are going to use... If you live in the US, Radioshack has several type of resistors perfect for the job you are attempting. I don't know what the conversion from euros to dollars is, but expect to pay about \$2 or more for one resistor...and remember, these aren't the puny ones for usb powered leds, these are monsters that can handle a lot of power...
Shinta7869 years ago
it depends on how much voltage you have. example: you have 12VDC power source and 3V leds, then you can wire 4 leds in serie, but I'd recommend to use all leds in parallel and using 12VDC resistors for each LED. the resistor should be soldered on the longer leg of the led (+) and the smaller leg is the negative side. resistors are cheap. You would pay about €1 for 100 resistors (or more).
collard419 years ago
You could have any voltage (up to 240V about, recommend a 12V transformer) the higher the voltage the more you can line up in a row, but it is better to put them in parallel. Tell me how many LEDs you are going to use (PM or Reply to this) and i can draw up a schematic and some resistor values