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custom led rings behind shroud?

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Member - Posts: 38
Member spacespace
Joined: October 08, 2012
Location: North Carolina, United States
Posted: October 31, 2012 at 6:24 PM / IP Logged  
working on my home made version of the "terminator eyes" for my retrofit install...been talking to a few guys over at hidplanet about it, wanted to clear up a few tech specifics before I start.
in my shroud, there are 8 holes where light can be seen from the front, I can't get solid ccfl rings or any led tubing inside because of the design, so I'm securing individual led's behind each hole.
my question, which wiring array would be best?
as of right now I have white led's
with a supply voltage of 12v running 8 led's...would a single series array be best? or a combination series/parallel work better?
a little help in this area would be great, I'm a bit new to the led scene...thanks guys
Member - Posts: 38
Member spacespace
Joined: October 08, 2012
Location: North Carolina, United States
Posted: October 31, 2012 at 10:28 PM / IP Logged  
a buddy of mine gave me a hand...
8 led's
4 parrallel circuits with each having 2 led's in series, with 220 ohm resisitors. 5% over what's recommended, but I would rather them be slightly less bright than burning out prematurely.
got a few bench wire pics...input and opinions are welcome (:
the led rings I bought were 90mm and didn't quite fit for my project, so I'm gonna sale them or whatever I figure out to do with them, if you're interested, pm me lol
the shroud with the led's inside is going over my quad-bi xenon retrofit for my trailblazer, should turn out quite nice after everything is done
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 01, 2012 at 5:57 PM / IP Logged  
Where did you get the lens from?
I'm actually looking for a flexible lens strip that can follow a curvy LED array, but that round lens has possibilities (I have round headlights).
As to the LED array - IMO definitely series & parallel and each series having its own resistor.
Your 220R resistor assumes 12V and not the up to 14.4V which is the long-term maximum that alternators can/should be set to. (Hence ~300R).
A 270R means 270 x .025A means a 6.75V drop added to 2x3.4V = 13.55V "max", 330R likewise means 8.25V for a max supply of 15V.
Hence maybe use a 330R resistor. (Power is 330 x .025 x .025 = 0.21W so 1/4W resistors are ok. I'd probably use 1/2W resistors which are more common etc.)
You'll probably find that using a larger resistor has little effect on LED brightness. (As does drops in vehicle voltage - the proportion of LED dimming will be far less than the proportion of voltage drop.)
[If dimming is a problem, constant current devices could be used instead of each resistor. That could be 2 transistor and 2 resistors, though I'd consider an LM317 with a 47R resistor (1.20V/47R = 25.5mA) etc.]
For 3.4V LEDs I was going to suggest 3 in series, but that might not conveniently subdivide into your set up of 8 LEDs (4x2) whereas it would be parallel 2 strings for 6 LEDs and 3 strings for 9.
Some might even use 4 LEDs in series (13.6V) with no resistor else maybe a 33R resistor (for 25mA @ 14.4V). The former is knowing that LED specs are somewhat optimum and they may tolerate voltages slightly above their rated or typical voltage. Same too with current, though above their rated current their life expectancy may diminish (maybe exponentially with the amount of over current.
I'd stick with "equal strings" - ie, the same number of LEDs with same resistor (each!) rather than mixing two 3 LED and one 2 LED string etc. That's more for simplicity and a single/standard design, but it should also prevent unequal brightness due to voltage fluctuations (even if probably not noticeable).
But in your case, since I presume you do not want to have to rework later if they blow (eg, risking(??) a 4 LED string, and since you have a nice 8-LED ring set up, stick to what you have - except perhaps reviewing your resistor values.   
Check the >12V issue with your buddy - he certainly seems to be cluey enough. (Yay! Regards from me.)
PS - yeah - it should be nice. It looks real good.
Member - Posts: 38
Member spacespace
Joined: October 08, 2012
Location: North Carolina, United States
Posted: November 03, 2012 at 6:37 PM / IP Logged  
so you don't think that 330 ohm resistor would effect the brightness enough to matter? meh a 25 pk of them on ebay are $1, screw it, why not lol
and I'm pretty set on the 4 strings of 2 in series, makes wiring the group of them more logical considering the inner contours of the shrouds. so I might order a 25pk of them and toss the 25 pk of 220 ohm's in my drawer, who knows, mods are addicting lol I'm sure they'll come in handy somewhere.
what lense are you referring to?
the solid round ring? I got it somewhere online, I forget the site, cheapest deal I found custom led rings behind shroud? -- posted image. but I'm actually not using them, they're 90mm and I have 4, if you're interested, let me know.
and for flexible strips, I recommend
the guys there are awesome, quick to respond to any questions, and quite helpful too...but I'm somewhat biased considering I've spent right at $700 there the past few weeks custom led rings behind shroud? -- posted image.
can't wait to get these lights done and so a write-up on them...gonna be worth every penny
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 04, 2012 at 5:18 AM / IP Logged  
Thanks for replying. Alas the rings are too small - I use 5-3/4" = 145mm round lights - not that I wanted "angel eyes" anyhow.
But that link is good. It didn't take me long to realise I wanted side-emitters instead of older/traditional LED strips. (I want to stick onto existing curved/horizontal contours.)
And I fully agree with your 4 x 2 LEDs. (If it were a case of minimising power consumption I'd argue 3 or 4, but that is irrelevant here.)
And "a mere" 2 LEDs per string (arguably?) makes it more tolerant to voltage fluctuations.
And yes - keep the 220Rs. They will probably come in handy one day.
[Besides, you can make a 330R with 2 parallel 220Rs in series with a single 200R. But hey - if cheap & convenient enough, why go to all that work? Besides, three 220Rs is 3x more unreliable than one 330R, but let's avoid "reliability" for now. You already have that with 4 lots of "2 LEDs plus a 1/2W 330R" per fitting etc. But if you become isolated and only have the 220Rs...]
The crap below {like the latter 330 = 220 +(220//220) LOL!} is superfluous if you use the 330R resistor.
Skip & ignore everything below unless you want my justification and a bit of theory, and maybe some insights for future stuff...
As to 330R vs 220R, the 330 is 50% more (resistance) than the 220.
What I'm saying is that it won't make 50% brightness difference... Nor 33% difference (220 is 33% less than 330 etc). I doubt it will even make 10% difference. (But I'd need the full LED specs...)
If you have a 330R then you could easily compare side by side.
And the 330R is based on a higher vehicle voltage than 12V - ie, ~12.6V with a fully charged battery, and usually up to 14.4V long-term when charging - though some alternators may go higher immediately after cranking (eg, 14.6V, 15V, & I've even known some from the 1990s to go to 16V & higher).
That relates to how do the LEDs tolerate "over" voltages (and current).
A sample calc:
Ohm's Law: V = IR (the voltage across a resistance equals the resistance (Ohms) times the current thru it (Amps).
[The units used are usually Volts (V), Ohms (R) and Amps (A) noting that we often use R instead the Ω symbol.
Assuming your LEDs are rated as 3.4V @ 25mA.
2 x 3.4V = 6.8V.
[Previewed Post - Oops - just noticed they are 3.3V @ 25mA, hence 6.6V across 2 LEDs. Tough luck - too late now... Read - I'm too lazy! Besides, just subtract 0.2V from the total voltages below. It doesn't make a big difference, and the principle doesn't change.]
Voltage across 220R (220Ω) aka the voltage drop across 220R = IR = .025A x 220R = 5.5V.
Hence max supply voltage for 25mA = 6.8V + 5.5V = 12.3V.
For 330R @ 25mA, V - IR = 0.025 x 330 = 8.25V.
Total voltage across two 3.4V LEDs @ 25mA & a 330R @ 25mA hence equals 6.8V + 8.25V = 15.05V.
(Likewise: 270R => 6.75; + 6.8V = 13.55V)
All I'm trying to show is that ASSUMING 25mA thru both LEDs & the resistor, the total voltages are 12.3V for 220R & ~15V for 330R (and ~13.5V for 270R).
Paraphrased, if your system never exceeds 15V, then the LEDs will not get more than 25mA if a 330R is used.
[ Whereas with 220R & 270R, of your system exceeds 12.3V and ~13.5V respectively, then the LEDs get MORE THAN 25mA.
Both 12.3V & 13.5V are typical in vehicles. A normal battery supplies more than 12.3V, and even old alternators will supply more than 13.5 & 13.6V (even when they used to be set to 13.8V; these days they are set higher = 14.2V being typical, ad 14.4V being the maximum). ]
Does that make sense? Or is this line also being skipped or ignored (LOL!!)?
A "12V system" is rarely 12V. It is usually up to 12.7V with the battery alone (not charging), and up to 14.4V and typically 14.2V with the alternator charging.
As to whether more than 25mA is bad depends on the LED. Maybe its a 30mA or 50mA LED.
But usually when spec'd or rated as 3.4V @ 25mA it means "at its max of 25mA it will last forever (or x-million hours etc) and have a voltage drop of 3.4V".
But that's a single-line summary of its specs. Go to its full specs and you may find it generally handles 30mA forever (but due to manufacturing tolerances or for extra margin, it is spec'd at 25mA), or that instead of 25mA forever, it handles 30mA for 5 years, 35mA for 6 months, and 40mA for 6.248 seconds.
If you want to know how the actual current varies with system voltage and a particular resistor (eg 330R), then you need its full spec - or at least its current versus voltage curve. (And those LEDs may be 3.0V @ 5mA, 3.2V @ 10mA, 3.4V @ 25mA (as rated), 3.5V @ 40mA, etc. They are NOT "linear" devices like resistors where V is proportional to I.)
And those current/voltage calcs get tricky since the LED voltage depends on the current, but the resistor's voltage drop also varies with that current...
Although it is reasonable to say that a LED's brightness varies in proportion to its current, it DOES NOT vary in proportion to its voltage nor the supply voltage, and (therefore) NOT in proportion to the resistance value. [Hence why PWM (Pulse-Width Modulation) is used for "proportional" dimming of LEDs. PWM effectively varies the current thru the LED(s).]
Member - Posts: 38
Member spacespace
Joined: October 08, 2012
Location: North Carolina, United States
Posted: November 04, 2012 at 10:46 AM / IP Logged  
^sound good? and holy crap thanks for the reply lol
as trivial as 90% of this stuff is, it's good to read it from someone else's "eyes"?? lol to reinforce what I had worked out in my head.
and as if I'm not already working on enough as it is...I have an idea for a pretty awesome led tail light...just gonna take a considerable amount of reading a prep before I jump into that
very few people would take the time to break it all down quite like you did...and I'm assuming you're like me, once you get us talking about something we like, it's hard to shut us up custom led rings behind shroud? -- posted image.
anywho...the led's and stuff should be coming in within a few days, until then, I'll be installing the Kicker L3's that should be here tomorrow :D *jumping for joy*
kudos sir, and until the next time...
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 04, 2012 at 7:55 PM / IP Logged  
Yeah, those resistors look fine.
I'd say "perfect", but that's based in part on an old "rule" whereby 1/2W resistors were considered more robust than 1/4W resistor. But I think that was merely due to the physical robustness (bigger) though at the time (when 330R was designated as a CCCXXX Ohm resistor ha ha) I took it to (also) mean electrical stability. But these days the 1/2W resistor I buy are the same size as the old 1/2 resistors.
However, using 1/2W instead of 1/4W means less heat - sorry - the same heat but it dissipates quicker and hence a lower temperature - and hence more reliable and a longer life.
BTW - until you order and receive, try the 220 in series with 2 parallel 220s. Just wrap them together and try with 2 series LEDs and compare to the 220R on its own.
FYI - I'm not used to mail ordering, I just head up to my local Jaycar store (maybe 5-8km away). I'd consider the need to constantly mail order a pain, but in practice it's probably cheaper, more resource & greenhouse friendly, and other than my childish "do it now" behavior would have no effect on WHEN I complete the project (not that I ever do!).
That reminds me... "...and I'm assuming you're like me, once you get us talking about something we like, it's hard to shut us up". Nah - I don't know what you're talking, er, writing about. custom led rings behind shroud? -- posted image. custom led rings behind shroud? -- posted image.
I merely have a tendency or compulsion(!!) to provide an entire education so the OP/reader can later DIY. And that often tries to pre-empt the typical (later) misunderstandings, tip & traps as well as throw in supporting experiences. And sometimes a bit of history else old spouse tales (formerly known as wive's tales) etc as well as modern trends. The above 1/4W vs 1/2W & web/mail-order guff may be a good example. There may also be the occasional politics etc like the environment, but that of course would be unprofessional on this site, and fraught with its own dangers! custom led rings behind shroud? -- posted image.
And I know the negative impact of my long rambles whether it be the key point being lost or a complete clouding and confusion or ignorance (as in my entire reply being ignored; bluddy english - too many uses for the same word!).
But it's for that type of "it's good to read it from someone else's eyes ... to reinforce what I had worked out" reason that I do what I do.
Mind you, I should write more "executive style" with summary or main points up top, then the optional detail later, or break it into more iterative posts (after prompting with questions), but I prefer a single "has it all" reply rather than the later (predictable?) replies.
Also my replies are definitely written with a view to later re-reads. That is the beauty of text forums.
It's very different when in real-time conversation. That's a bit at a time which flows in response to the real-time feedback (questions, bewildered looks, etc). The ramble is only when needed or useful and may be with an "FYI-only" warning.
Verbals merely require knowing what needs to be conveyed and in what time. The delivery then varies greatly, but usually in executive style - ie, sequential high-level summaries and see what needs extra info - aka a drill-down into detail basics etc.
Alas I prioritise too little time to web forums. I hence race thru reads and replies.
The raced reads are usually ok though my recent/yesterday's reply on "12v light flasher" is a classic on how bad that can be!.
But my raced replies... Let's just say that I usually shudder when I re-read them later!    
At least in my previous reply above, I separated the "short reply" from the extra stuff/ramble that followed.
I should definitely plan my replies, else write and review later BEFORE submitting. But I'm way too busy for that!
[ That last is a bit of a joke. Planing saves time. And verbiage! Besides, it's a case of prioritising as essentially everything is (very few people "didn't have tie for..." - what they mean is it wasn't a priority - at least when it came to actually doing things - ie, they did not or could not plan/prioritise). Ooops - personal politics!   custom led rings behind shroud? -- posted image.
Maybe the birthday card I recently got from my girlfriend puts the frivolousness of my "I'm way too busy for that!" into perspective - see hattyboots-imgcards-SD577 - it's become a bit of a catchphrase. ]
Anyhow, enough ramble. (What - me ramble? Never!... - my common forum catchphrase.) Quack quack!
Ok, so people give up and miss my point(s) of importance.
In this case it's that we live in a world where lots is done and it "set" for us. We can't modify or build-your-own things like we used to.
To see people doing their own and adding their own flavors IMO is to be commended - especially when it involves research and learning which IMO might be a severely lacking trait these days.
And this project - which IMO probably enhances safety as well as looks - could be the start of a new splinter hobby, else enhances an existing hobby (ie, vehicles, vehicle electrics or lighting, etc).
Ok - you're probably astute enough to see that I'm trying to suck you in to a stream that will cause you heaps of frustration and angst. Suffer buddy - since we suffered, we want you to suffer too! (By "we" I mean "I" in case others wish to disown that comment LOL.)
Anyhow, hence I enjoy helping..., er, I mean... writing.
As to future taillights, there are a few threads, and maybe some are on I'll try to find them and link in a reply.
In the meantime, I'll pre-warn you of another word - "PICAXE". That's my due-diligence so you don't die at once. You can therefore die slowly like the rest of us - I mean, me. (See, I am a responsible citizen! custom led rings behind shroud? -- posted image. )
And I didn't mention my sense of humor. What humor?
As to long replies and me ramble? Indeed!
Member - Posts: 38
Member spacespace
Joined: October 08, 2012
Location: North Carolina, United States
Posted: November 04, 2012 at 10:13 PM / IP Logged  
Actually, I quite enjoy the rambling (and besides, if what I'm doing is time sensitive, there is always ctrl+f hahaha)
it tends to lighten the mood a bit and reduce stress that these projects tend to bring out.
I couldn't agree more on your point about people not diy'ing enough these days. I would rather bang up my knuckles, burn my hands with soldering irons and lose sleep doing it myself. But, like you say, that's just me custom led rings behind shroud? -- posted image.
I've actually stumbled on a few threads about pic controllers...also 556 timers. I assume they would be used in conjunction with each other? Maybe not, having quite researched them enough at this point.
The nearest retail store that sales component parts like I need is about an hour away, so yes, mail ordering is considerably easier for me. (until it's 0200 and I'm out by my work bench and see that I goofed an order and forgot something.
Suffer? HA! I love learning new things, and being told something, isn't learning, it's being crippled custom led rings behind shroud? -- posted image. ::though somehow I see myself regretting that statement later hahahaha
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: November 05, 2012 at 12:25 AM / IP Logged  
Always question or at least be open-minded about things you are told. The number of incorrect "facts" that I still read... OMG!
That goes for me too - I have been wrong etc.
Sensing something is wrong doesn't always require knowledge per se, it's more a case of logic and imagination. My oft quoted {Kerrigan's} line "It's not what you know, but how you think." - that referred to solving so-called unsolvable problems.
Banging knuckles and burning hands - that's us! Yay to us masochists!
Ah yes, the 556. It's a dual version of the 555.
I tended to avoid them since they rarely seemed to work for me whereas two 555s would. Maybe I had insufficient decoupling - the typical 0.01uF or 0.1uF capacitor near and across the power pins to swamp voltage transients caused by internal switching (which was quite prominent in the 555).
But the PIC (PICAXEs etc) replaces the 555. Why?...
Though maybe not relevant here, IMO one big consideration is that for power sensitive applications - the 555 draws a minimum of 10mA. That's equivalent to half a LED and that can even effect big car batteries (after a week of few).
Compare that to a PIC - eg, the PICAXE-08M which draws nA in standby and uA in operation.
[ Pasting from's hardwiring Labtop DC-DC converter directly to battery. ie bypass any switching relay Post #14 and noting that PIC12LF1840 is one version of the PIC 08M:   
From doc DS41441B - Low-Power Features:
- Standby Current (PIC12LF1840): - 20 nA @ 1.8V, typical
- Operating Current (PIC12LF1840): - 34uA @ 1 MHz, 1.8V, typical
- Low-Power Watchdog Timer Current (PIC12LF1840): - 300 nA @ 1.8V, typical.
... ie, 34uA in full operation; 300x less than a 555 in standby.
I mention the above because of the number of times I see the 555 forummed for use for some "standby" application like sensing solar panel voltages or loads.
That's a ridiculous application of the 555 when there are relatively simple discrete circuits that will do it with negligible power consumption.
[It's a case too where people think only of how simple that function may be implemented using the 555 and forget the big picture - eg, using a relatively high-power circuit with a low capacity power source.]
But the main reason for using a PIC is the relative cheapness and versatility, and that changing things may be a mere program change rather than a component change etc.
A 555 is merely a timer though its brilliant design extends its application to other things.
The PIC however is essentially a CPU - a computer chip. It can do lots of things - logic switching, sensing, dimming, alarms, sequential processing/outputs etc.
A PIC usually needs less components and ironically can be cheaper than a 555 (circuit).
But I'll leave further discussion to other links.
Besides, it was merely a forewarning LOL! But since usually taillight ideas usually involve switching and dimming etc, and usually LEDs, a PIC is the go.
Even a simple dimming of "dual function" stop & tail LEDs (as opposed to separate LEDs for each) is IMO easiest done with a PIC. Add to that any need for combinational switching - eg, stop or tail (parker) LEDs of whilst flashing (or reverse lights off when flashing for non-Yankees) - and the PIC is definitely the go.
As to links, I had in mind a certain "custom taillight" with various display patterns (stop & flasher where the flasher sequentially lit (7?) bands of LEDs from the center outwards).
Also a thread where it started with someone wanting whatever that could have been done with whatever "normal" analog methods could have been used, then me reluctantly or temptingly mentioning or suggesting a PIC, and the final outcome being the OP using the PIC solution.
(Maybe the same thread? "Discrete chip" equivalents involved the 555 & maybe 4017 one-of-ten decade counter chips)
The points being (1) the OP saw the desire for the PIC, & (2) the OP found it was NOT difficult after all. (As I recall, the OP was familiar with other programming, but IMO learning or using (copy & modifying) PIC programs is easier and quicker than understanding analog electricals and electronics.)
Anyhow, some of the links I found follow below.
Note that they may be several pages and I might have merely given a "key page" that I found, but maybe some or the rest of the thread also has good info.
And they may involve other platforms like the Arduino - the point being that they are both programmable (albeit the Arduino is a package that uses a full computer chip whereas PICs are merely a chip which is a simplified and cut-down CPU (computer) with some inbuilt peripherals (that's a hasty and not totally correct nor consistent comparison, but hey!)...
... and in principle, it's the coding or programming that is the essential driver (no InfoTech-puns intended) to get things to work as you want, and those conceptual steps should be convertible to other platforms (chips & systems). ["Everything is the same, only different" to quote one anonymous source.]
Anyhow the links - hoping they are relevant, or give you some ideas.
I think I even found at least one of those I mentioned - they might even be the one thread and not separate threads - I haven't checked...
(BTW - I blame the rain for this. I was going to continue my electric window install. And dammit - now the rain seems to have stopped...)
First - how small a PIC can be and some pre-fabricated "basic" PCB assemblies from the aforementioned mp3car link but showing the AXE230 & RKP08c kits.
Now the rest....
the 12volt's basic l.e.d. wiring;
Ah-ha, maybe this is the aforementioned "PIC is easy"... the12volt's single pulse on/off latch relays and its The PIC chip ... is 100% ideal for a project like this;
mp3car's recommendations for attiny or arduino newb? (merely for PWM'ing LEDs??! Use a 555 else PIC!);
Actually the others don't look hugely relevant, both at mp3car here and here, though I note my dig at someone, and the usual PWM etc comments.
Yep, it's dry outside. Good - that means I can further delay having to think about my other botched thread...
Member - Posts: 38
Member spacespace
Joined: October 08, 2012
Location: North Carolina, United States
Posted: November 05, 2012 at 11:59 AM / IP Logged  
so the pic controller could handle the dim/bright and chase functions all on it's own?
I read over the post, just need to do some in-depth reading on the controllers. I know a guy that's a computer programming major, may have to buy him a beer to help with with the programming part custom led rings behind shroud? -- posted image.
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