LED lights need help guys.

[Doc]

Need help guys.....

my understanding off electronics is rather limited. I have a wixey angle guage and want to illuminate it with a couple of red Leds's.

I want to run it from a 12v battery and perhaps if it's not to difficult have a swith to turn it on and off.

What would I need. I persume i need some resisters but which ones.

A schematic would be great.

[barkis]

I'm sure I used a 1.8K with a 12volt supply Doc. I am sure you know that LED's are polarity concious, and have to be connected only the right way, otherwise it will damage them. Wait for confirmation of my suggestion, I going from memory.

Ron.

[Doc]

Ron by polarity concious you mean they only work if wired correctly. They only work one way.

[Parallax]

Asusuming that the LEDs are 2 volt and 20 mA, then, to run them off 12V you will need to 'drop' 10 volts across a resistor. From Ohm's Law, R=V/I. So, R=10/.02 which equals 500 ohms. The nearest resistor that you can get to 500 is 510. You can go higher than this although the brightness is affected (more ohms, less light).

Connecting the LED the wrong way round will not damage it.

The resistor goes in series with LED.

Steve

[blinky]

You can also get 12v led's these basically have the resistor built in

[Doc]

So Steve if I have 2 LED's both 2 volts that means I have to drop 8 volts accross a resister.

So what resistor will I need. I make it about 430 ohms.

Where do I place the resister in series. Is it before the Led's or after.

[PhillyDee]

I have 50 330Ohm resistors for exactly this purpose. PM me your address and I will send a couple out. 3 do you? Or do you want a couple more? LEDs tend to be 2-4v, so these will do you fine.

[Doc]

You can also get 12v led's these basically have the resistor built in

Cheers Craig I'll try and find a web site on these.

[blinky]

Most places will sell em, they are only a few pence more than the normal ones. Maplin do them

[Doc]

I have 50 330Ohm resistors for exactly this purpose. PM me your address and I will send a couple out. 3 do you? Or do you want a couple more? LEDs tend to be 2-4v, so these will do you fine.

Cheers Phillydee.

Just a question I've worked it out that I should need 430 ohms, so will 330 ohms do me. As I've read another website that states resisters are not really needed, it is just there as a back up in case of trouble.

So would this work

(+) 12v ----- 2v Led -----2v Led ---- 330 Ohms Resitor ------12v (-)

[Psychobilly]

hmm they are certainly needed...

Billy...

[Doc]

Most places will sell em, they are only a few pence more than the normal ones. Maplin do them

Cheers I've found them in Maplins.

[Parallax]

So would this work

(+) 12v ----- 2v Led -----2v Led ---- 330 Ohms Resitor ------12v (-)

Yes, that will work. 2 points though :-

1. You will be driving the LEDs a bit hard, although they will take it,

2. If 1 LED fails then obviously the other will not light.

Alternative layout :-

(+12v)--¬----LED-----510 Ohms--¬--(0v)

| |

| |

----LED-----510 Ohms----

Steve

[ringz]

Doc,

20ma through an LED, depending on the LED type, will likely be blinding. Perhaps you might want to do a bit of experiment to find a value that illuminates the Wixey adequately and doesn't blast your night vision.

--

Martyn

[Rooster]

(+) 12v ----- 2v Led -----2v Led ---- 330 Ohms Resitor ------12v (-)

Is the circuit I would use... but the resistors are a little "small"

The resistor does as it says... resists electricity ! (well, current to be accurate) hence the bigger the value, the more it resists, so - a larger value will "hold back" more current... and present a dimmer LED.

For 12vdc my stock resistor is 1k (one thousand Ohms) although this may STILL allow too much light from the LEDs... its surprising just how little light the eye can see when dark-adjusted.

A resistor costs 15p from craplins, sorry Maplins... (they are awful these days) so why not get a few ?

say:

1k (bright)

10k (dimmer)

50k (dimmer still)

And experiment ?

[philsail1]

Doc,

I went to "Maplins" (I wanted to light up my Polarscope) and told them what I wanted to do, and they worked the whole thing out there and then, recommendind the right LED's, resistors and circuit. They even provided a printed schematic for me to follow when making the circuit up. The toal cost in my case was about £4.00.

Regards,

philsail1

[Rooster]

Doc,

I went to "Maplins" (I wanted to light up my Polarscope) and told them what I wanted to do, and they worked the whole thing out there and then, recommendind the right LED's, resistors and circuit. They even provided a printed schematic for me to follow when making the circuit up. The toal cost in my case was about £4.00.

Regards,

philsail1

You got lucky then... our local branch has more staff than customers and put together, I doubt they could manage a 2 piece jigsaw puzzle !

Couple of weeks back I had an argument over "2 Meg" resistors... "we call them 2 Ohm sir" FFS this went on for 10 minutes, with 3 staff !!!! in the end I drove 15 miles to a REAL electronics shop - and paid 1/8 the price !

As an "add on" if anyone wants help, or even any electronics building - I am quite "au fait" as they say !

[Tinners]

Here's a nifty calculator for leds

http://led.linear1.org/1led.wiz