# Help with simple LED circuits



## Bottle (Feb 3, 2015)

I'm super new to building circuits, as in I've never built one before, and basically have no idea what I'm doing. I need to either make about 13 small circuits, each with a small white LED and an on/off toggle switch, but I have no idea how to figure out the logistics of it, or where the best/cheapest place to buy parts would be. Could somebody walk me through building a circuit like this and suggest a website to buy parts on and which parts I should buy from said website? I do hope I'm not asking too much.


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## Vegassparky (Nov 24, 2013)

What is the power source, and is anything else going to be controlled from the switches, with the LEDs functioning as status indicators?


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## Bottle (Feb 3, 2015)

I figured I'd use CR2032 batteries. The LEDs are the only things the switches will control and are not intended to work as status indicators; they're being used to light up small stands.


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## gcavan (Aug 13, 2009)

This will be your basic circuit. 









First choose The type and color of LED you will use. Consult the manufacturer's specification sheet and find the Forward Voltage Drop (Vf) of the LED. 

Decide on a power supply. You require something with a voltage greater than the forward voltage of the LED. A CR2032 is about 2.8 volts, which is just barely enough for a single red LED. Other colors will require a higher voltage source. Also, the CR2032 has a capacity of about 200 mAH, which gives 8 - 10 hours of On time for a single LED.

Your LEDs will be instantly destroyed if connected directly to the power source, so a limiting resistor (R) is used to limit the current through the LED. Calculate the resistor value with the following formula:

R = (supply voltage - LED forward voltage) / LED current

Assuming a CR2032 and a typical red LED (forward voltage = 2.0 volts), the limiting resistor would be 40 ohms. 

The LED is polarity sensitive. The anode (A) lead of a new LED will be slightly longer than the cathode (C).


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## Bottle (Feb 3, 2015)

If a CR2032 is just barely enough to power a red LED, would I be better to use a different type of battery? I haven't ordered any batteries yet so I'm flexible on what I can use. The LEDs I'm likely going to order are stated to have a forward voltage of 3.0-3.2 Volts.


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## gcavan (Aug 13, 2009)

> The LEDs I'm likely going to order are stated to have a forward voltage of 3.0-3.2 Volts.


A single CR2032 is not going to cut it. You could use two in series and then a 120 ohm resistor.

Question: Must each circuit have its own power supply? Any reason you cannot use a single 6 or 12 volt wall wart to power them all?


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## Bottle (Feb 3, 2015)

I need to be able to arrange the stands individually so it'd be better if I had each one self contained. Two CR2032s per stand should do, though!


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## MPR (Aug 28, 2010)

This calculator might come in handy.

LED Calculator - Current limiting resistor calculator for LED arrays


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