Question for the LED knowlageable

[POPEYE]

I want to make my own tail/break light bar, haveing seen BDT's only with more leds than that contained, how do i wire em so they are not so bright when tail light are on but go to full brightness when breaks are used, i believe useing a high value resistor will "dim" them but what value? the bar i worked on seems to have been made up of banks of four leds controlled by two (different value) risistors, i should have checked the colour codeing but did'nt think and now it's all sealed up, been looking at several google'd sites and it appears you can wire four leds in series without a resistor and am i right in thinking if say five or six were wired the same it would reduce the brightness,
(this is working on led of 3v) any help would be great,
ian

[That Ruddy Squirrel]

[scuttles in and posts this before running for cover as Ian drools]


ps ask them and they should deliver over here

[POPEYE]

Want to build a custom bar Trev, and half the fun is doing it yourself

come on where are the elecrticle boffins????

[BUSHWHACKER]

Any help?

http://www.the12volt.com/installbay/...ics.asp~FID~18

[POPEYE]

Already asked on there Vince, a couple of threads sort of cover it but no real explanation, downloaded several bits from a google search, some of which is helpfull, if all else fails the guy at Phenoptix might be able to help with resistor values especially as i'll be buying several hundred leds off him

[MattF]

Two sets of L.E.D's. One set wired with a <2K resistor inline to the tail lights, and the other set with a <1K inline to the brake lights.

[POPEYE]

If i'm unable to find out how to do it by reduceing voltage to them for tail light and increasing it for break (useing the same leds) i'll probably do it that way Matt, cheers, a simple circuit of say four leds that i can then multiply to suit my
application is what i'm realy looking for, i'll sort summat out, i expect the solution will come to me in the middle of the night

[nero279]

just as a kinda dodgy semi thought something running through my mind sort of thing, what would happen if for example you had a bank of 16 leds arranged in a square. And sort of wired as in the dodgy picture below, so you have 5 possible wires on the right hand edge you could put either a positive or a negative on, obviously some scenarios none of the LEDS would light - eg if you only had positives or negatives the wrong side of the LEDS, some they would all light up, and some scenaios, ie) a + in the middle somewhere and - at one end only some LEDS would light up, but would any scenarios cause them to all light up at part brightness or could you change switch the polaity of any of the LEDS to get that effect..........


........ is anyone still with me or should i just stop thinking?

[truckarms]

dont know if this would work but could you not set the LED's up in series (i.e. they share the 12V) thus making them not very bright but run them in parrallel when the brake pedal is pressed (i.e. they each get 12v)

dont know if leds work like that, but that should work with normal bulbs

[POPEYE]

just as a kinda dodgy semi thought something running through my mind sort of thing, what would happen if for example you had a bank of 16 leds arranged in a square. And sort of wired as in the dodgy picture below, so you have 5 possible wires on the right hand edge you could put either a positive or a negative on, obviously some scenarios none of the LEDS would light - eg if you only had positives or negatives the wrong side of the LEDS, some they would all light up, and some scenaios, ie) a + in the middle somewhere and - at one end only some LEDS would light up, but would any scenarios cause them to all light up at part brightness or could you change switch the polaity of any of the LEDS to get that effect..........


........ is anyone still with me or should i just stop thinking?

Not at all sure i'm with ya on this but i think any way you connected your feed and neg would only light some of them where ever you connected it, not sure tho, i think all anodes have to connect to anodes and cathodes to cathodes when in paralel, series its like a daisy chain, cathode to anode and so on with a + &- each end,
i was thinking if i connect a line of leds in paralell feed through high value resistors to reduce their brightness this would give me tail lights, then if i could feed then with higher voltage (lower value resistors) they would go brighter giveing me break lights, only thing wrong with this that i can see is the current from tail lights circuit would feed back through the low value resistors causeing the break light to come on (all of em) as current flows through a resistor both ways, think it'll be easier to go matts way and have two seperate circuits,
my head hurts now

[POPEYE]

dont know if this would work but could you not set the LED's up in series (i.e. they share the 12V) thus making them not very bright but run them in parrallel when the brake pedal is pressed (i.e. they each get 12v)

dont know if leds work like that, but that should work with normal bulbs

Dont think it'd work, i think the maximum voltage to one led without a suitable resistor is 3v without it blowing, so four in series will get 3v each without a resistor needed (am i right?) in paralel they would get 12v each and blow without a resistor, dont think you can cross between series and parllel, know what you mean tho

[That Ruddy Squirrel]

All this for 2 banks ?

Is it not worth going the whole hog and having a 3rd bank in amber (split in two) for the indicators and a 4th bank of white for reverse ?

[passes Ian a LARGE bottle of headache tablets ]

[POPEYE]

All this for 2 banks ?

Is it not worth going the whole hog and having a 3rd bank in amber (split in two) for the indicators and a 4th bank of white for reverse ?

[passes Ian a LARGE bottle of headache tablets ]

or the whole thing, like a jap taxi

[MattF]

Nowt like being awkward.

Tail lights 12V ---|diode|--|resistor|--[BL connection point]--|resistor|--|L.E.D's


Brake lights 12V ---|diode|-----[connected to BL connection point]


That should do the business with a single bank. Both resistors would want to be around 1K, or possibly slightly less. I think 560ohm is about the lowest safe value. I think I used 680ohm on my L.E.D's.

[darkdezigns]

I want to make my own tail/break light bar, haveing seen BDT's only with more leds than that contained, how do i wire em so they are not so bright when tail light are on but go to full brightness when breaks are used, i believe useing a high value resistor will "dim" them but what value? the bar i worked on seems to have been made up of banks of four leds controlled by two (different value) risistors, i should have checked the colour codeing but did'nt think and now it's all sealed up, been looking at several google'd sites and it appears you can wire four leds in series without a resistor and am i right in thinking if say five or six were wired the same it would reduce the brightness,
(this is working on led of 3v) any help would be great,
ian

on a diff note can i pop down saturday,lunchtime ish to pick up?on way thru to rods?if so can u pm addy,many thanks!