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Probably the most basic question you'll read this year

hardwidge

Nov 21, 2011
2
Joined
Nov 21, 2011
Messages
2
Hi all,

I'd like to create a simple circuit with a small white LED, a switch and a battery.
I'd like it to be as small as possible, and ideally using a cylindrical battery (as opposed to a flat one) although this is not essential.

What I'd like to know is:
a) What's the (physically) smallest battery and LED I can use,
b) Do I need to use a battery housing or can I solder straight onto the battery? and
c) How the hell do I put it all together?

Sorry if this is the wrong place to post this thread too, I'm new here :)

Cheers
Tom
 

davelectronic

Dec 13, 2010
1,087
Joined
Dec 13, 2010
Messages
1,087
Hi hardwidge.
Welcome to the forum, what you want to do is really quit straight forward and easy enough to do, i will put to links below for some explanations on led circuits, the first is a forum help thread by Steve one of the moderators the other is a small web site on components use and applications, good little site. As for battery size you can go really small, but dependent on the led's power requirements will determine how long it will stay lit up for.
Dave. :)

Got a question about driving LEDs? (Another work in progress)

LEDs (Light Emitting Diodes)
 
Last edited:

hardwidge

Nov 21, 2011
2
Joined
Nov 21, 2011
Messages
2
Hi Dave,
that's ace thank you for your help. I'll check out the links and see how I get on.

Cheers
Tom
 

daddles

Jun 10, 2011
443
Joined
Jun 10, 2011
Messages
443
What I'd like to know is:
a) What's the (physically) smallest battery and LED I can use,
b) Do I need to use a battery housing or can I solder straight onto the battery? and
c) How the hell do I put it all together?
a)

Note things probably won't be quite as simple as you're assuming. Common batteries have typically around 1.5 volts when new and will drop in voltage to around 1.2 V or so over their operating life. A typical white LED might have a voltage drop of around 3.5 volts. Since you always want to put a resistor in series with the LED, you'll find that you likely can't operate an LED with a single battery. Even a CR123 isn't good enough. Of course, I could say "use a 6 volt lantern battery", but that's probably not what you had in mind.

There are circuits that will let you operate a white LED on a single 1.5 volt battery (I keep a flashlight on my keyring that runs on a single AAA battery), but to do so will require a circuit construction, which may be a bit of a challenge for a beginner.

b)

It depends on the battery and your soldering skill. I've soldered to AA, AAA, C, and D batteries many times over the last few decades and never had a problem. The basic technique is to keep the soldering heat conducted into the battery to a minimum. The typical warning is that you can cause a battery to explode if you put too much heat into it. I've also soldered to a few lithium coin cells; those require fast techniques because of their small thermal mass.

For a beginner, I'd recommend using a battery holder.

c)

One piece at a time, just like eating an elephant. :p For safety and robustness, the best solution is probably to mount it into a small project box. You can scavenge or buy these.
 
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