# Hooking up one LED



## cbmar (Sep 20, 2006)

I need to hook up one LED for my Terminator costume.
I bought a 5mm, 1.8 volt, 20mA, 120mcd - red LED.
I tried connecting it to a 9 volt battery and it blew immediately.
How do I get this to light without that happening? Resistors or something? Different battery?


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## spinman1949 (Jun 29, 2009)

*Use a button battery*

I have flying ghoulies that I put led's in for eyes. They all run off a single 3 volt button battery. No resistor required. Been working now for years and only replaced one battery so far. I just solder right to the battery. You need to file the surface of the battery and use a good iron. You pre tin the connector and the battery to keep down the time you are heating the battery. Oh each ghoulie has it's own battery. Not sure if you can find the battery holder for a button battery. You could also just try a single AA battery. If that does not work, then try two.


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## cbmar (Sep 20, 2006)

spinman1949 said:


> I have flying ghoulies that I put led's in for eyes. They all run off a single 3 volt button battery. No resistor required. Been working now for years and only replaced one battery so far. I just solder right to the battery. You need to file the surface of the battery and use a good iron. You pre tin the connector and the battery to keep down the time you are heating the battery. Oh each ghoulie has it's own battery. Not sure if you can find the battery holder for a button battery. You could also just try a single AA battery. If that does not work, then try two.


What do you mean by "pre tin" the connector?


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## pshort (May 6, 2008)

Pre-tin means that you apply a thin layer of solder to the leads before trying to solder it to the battery (or whatever).

However, I don't think that using a single 3V coin battery is going to work very well with red, yellow, orange and some green LEDs (although blue, white and some green LEDs should more or less work). The battery voltage is too high for the LEDs that I said won't work too well, and you would need a current limit resistor to work with them.


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## spinman1949 (Jun 29, 2009)

*They work fine.*

I bought an assortment of led's from radio shack. I have Red, Green, Yellow, White. I have round and the slit shaped rectangular. They all work fine and none has burnt out. Now just to be sure, I will check the batteries, but I am fairly sure they are 3 volt. They are the same batteries we used to use to protect memory on circuit boards. I don't think 1.5 volts would do it.

But to be correct, one should use a resistor I am told even if the voltage is close. Since the led's are cheap, and the batteries were free, I figured why bother. Like I said. I have these ghoulies running on an Axworthy now for some 8 years.


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## pshort (May 6, 2008)

I looked up (on the most reliable of sources, the internet) the internal resistance of a CR2032 battery comes out to about 20 Ohms. The current through a red LED is then about 50 mA with a fresh battery. So I suspect that what you would see is a fairly bright LED for about 4-5 hours, then a somewhat dimmer LED for a much longer time.

In any case, I would go with Spinman's recommendation as a test, assuming that you are not paying full retail for the battery.


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## hedg12 (Jul 6, 2008)

If you want to continue using your 9V battery, wire a 390 ohm resistor in series with the LED.


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## fritz42_male (May 5, 2009)

I use CR2032 button cells for all my LEDs in skulls and so on and never had a problem without a resistor. I use the holders with wire soldered on and then push a thin piece of card into the holder as an on/off switch. The batteries have a long shelf life so getting 3 or 4 years out of them isn't a problem. This is the holder I use

http://cgi.ebay.com.au/CR2032-CR202...gers?hash=item1c0cf2a5e8&_trksid=p3286.c0.m14

For lamps I have a load of small translucent orange pumpkins, put some blu-tac inside, push the buttton cell on edge into the blu-tac and then push the LED onto the cell. These work for a week before dimming.

I pick up high brightness LEDs, CR2032 batteries and CR2032 holders on eBay - it works out at about $1 per LED and battery and about $1.10 for the combo with a holder!

If you really want to then wire a 50-100 ohm resistor in series but I don't bother.


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## BTH (Jul 2, 2006)

I just ordered these batteries. Don't know how good they will be, but they sure are cheap!!!! http://www.dealextreme.com/details.dx/sku.751


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## fritz42_male (May 5, 2009)

Perfect and you can tape the LED on if needed rather than use a battery holder or whatever. Long lead on the LED goes to the PLUS side of the battery.

My LEDs last about a week on one of these - 24 hours a day.


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## Jaybo (Mar 2, 2009)

Here is a good article from Instructables on LED Throwies. No solder needed. Just tape, LED, and a battery.


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## fritz42_male (May 5, 2009)

Just as an aside, if anyone is looking for a good terminator/android effect, buy one of these cheap flashing led brooches and use one of those behind some scrim fabric over an eye or on the head. The pinpoint flashing LEDs make for a good effect - all for $2


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## cbmar (Sep 20, 2006)

*One more question...*

It worked great. Thanks. One more question though...
If I want to add a second LED to the same set-up, do I need to use a resistor with a different number of ohms, or should the same resistor work regardless of whether there are 1 or 2 LED's plugged into the battery?



hedg12 said:


> If you want to continue using your 9V battery, wire a 390 ohm resistor in series with the LED.


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## Otaku (Dec 3, 2004)

Assuming the second LED has the same specs as the first, you'd need a 270 ohm resistor. The 390 ohm that you're now using will work, but adding a second LED will cause them both to be pretty dim.


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## xdmray (Oct 4, 2009)

you need to run much less voltage throught that LED. you have to match the levels to have it run optimum. a 1.8V LED needs 1.8V of battery. 9V was way to much. use less voltage and a resistor. use this calculator http://led.linear1.org/1led.wiz to help


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