hi all!
need a favour if anyone could be kind enough to help me out? i'm actually into scroll sawing and mainly make and create tree hangers for christmas, my projects for next year will be making 'schwibbogen' its an eastern german craft i think it roughly translates to candle arch or lighted arch ........i think :confused: i'll try add a pic as an example so you get the idea if you've never heard or seen them before (but i find them stunning).

EDIT: sorry don't have the reqiured number of posts to add a link or pic :( but you can google it no prob and look at the image results

Now to my actual Q?
the arches are all lit as you can see, but use mains electric, this is something i was hoping to avoid. i'm looking at using as few as 5 LED's with a 9v rectangular battery as a power supply as i don't fancy playing with mains elec at all :confused:
they don't need to be super bright just nice backlighting, so could anyone please give me a hand and tell me what sort of LED's i should use, with which resisters, also is this a good idea as i'm unsure what sort of battery life i'll get from the the 9v..........and last but not least just to push my luck a bit more could you include me a little wiring diagram :)
many thanks
Jay
oh one more thing :rolleyes: just out of interest what would the difference make between wiring in parallel or series?? is it down to battery life and if so which is better? or is there a different advantage?

Hi,

I won't answer all your questions, because I don't know what LEDs you can get your hands on. But a few things I can tell you.

1.) Use warm-white LEDs. As the name says, it's a much warmer light. You could also use amber LEDs, but you just have to see what you like best.

2.) Parallel wiring of LEDs is sort of a DON'T in electronics, so you should settle for serial wiring or a combination.

When you buy LEDs (or before :-) you can get a look at the datasheet, where you can find the nominal voltage and current for 1 LED. Most online-shops put those values in the detailed description.

Example: 3mm warm-white LED, 3.1 V, 20 mA typ., 30 mA max.
Values are for a superbright LED, which may be a little too bright for a christmas tree. I will give you an example for using both typical and half current (10 mA).

Depending on the amount of LEDs needed and your battery voltage, you have a few options.

Example: you use a 9V battery and need 6 LEDs. When wiring LEDs in serial, the voltage adds up. So: 1 LED -> 3.1 V; 2 LEDs -> 6.2 V; and so on. In this case 3 LEDs would be a little much, the voltage would be 0.3 V over the battery's capability, so we settle for 2 LEDs. Now we can subtract that voltage from that of the battery (9 - 6.2 = 2.8 V) and you have the voltage for the resistor. The current is the same of the LED (10 or 20 mA). So now we can calculate the value of our resistor. Let's say for 20 mA.
R = U / I -> R = 2.8 / 0.02 = 140 Ohm
Now for 10 mA:
R = U / I -> R = 2.8 / 0.01 = 280 Ohm

You normally get a 150 Ohm or 120 Ohm resistor, or for 10 mA a 330 Ohm or 270 Ohm resistor. I suggest buying the 150 Ohm. If you want to use 10 mA, just wire a second resistor before the first, and there you go.

I can't put a schematic online, but I'd be happy to email you one. Just PN me.

Anyway, now you should have (in serial wiring) 1 (or 2) resistors and 2 LEDs.
To get the other 4 LEDs, just make 2 more sets of the above and connect them parallel to the first setup (meaning directly to the battery :-)

Then you have 6 LEDs driven by a 9V battery. That should give you at least 6 hours of light when using 20 mA or 12 hours when using 10 mA.

I'd be happy to help you devise a schematic, depending on the LEDs. Just contact me.

Hope I didn't make your head spin ;)

Greets

Tom

Hi Tom,
i've not logged on in a while and just wanted to thank you for taking the time to reply :thumbsup:
i've been reading up and researching some basic stuff but was glad to have a read of your input to
i've just recently......only on the past couple of days come across this site it and it allows me to enter the info just like you've already mentioned (voltage,ma,ect...) it will even draw you a schematic, wiring diagram it'll also help with colour codes of resistors if you need and offers you different ways in which you can wire the LED's (if variables are available).
i'll add a link if i can or leave the web address as i'm taking it as read that what it does is correct so a 2nd opinion would be great, and you never know it may be of use to someone else out there ;)

aaaargh!! still won't let me post links or pics as i don't have the reqiured amount of posts i'll submit this then try again :p

http://led.linear1.org/led.wiz

here we go!!:thumbsup:

ps just checked out the warm white led's, they look great possibly ideal for what i need, thanks again :)

A pleasure to help :-)

If you need any more help, just PN me or post something here, I'll be checking regularly.

Greets

Tom