Some electrical advice, if you would be so kind ;) DIY LED case mod

d_brennen

d_brennen

d_brennen

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Well, it has been a very long time since I last wielded a soldering iron in anger (over a decade at least) but I have come into possession of a nice little butane model.

I want to make some custom lighting for my case, something very low key, just to pass the time while the weather is still pants. What I do want to do is use LEDs and power them from a molex connector from my PSU. What I don't want to do is fry my PSU/burn house down/electrocute myself.

Ideally I'd like to use 4/6 bright white LEDs on one loop. Haven't looked around for specifics yet although there is one of those "large component retailers" just around the corner from me.

Has anyone on here done such a thing? Would appreciate some input/links where possible. Oh and no "you can buy this, that or the other that will do the same" please. I'm wanna have some fun, learn something and have something unique! :)
 
Found these on said component retailers site. They are high intensity 5mm white LEDs:

Absolute maximum ratings: Ta = 25°C
Power dissipation: 108mW
Peak forward current: 100mA
Continuous forward current: 30mA
Derating factor: 0.4mA/°C
Reverse voltage: 5V
Operating temperature: -25 to +85°C
Storage temperature: -35 to +100°C
Soldering temperature: 260°C / 5secs
Absolute optical characteristics:
Ta = 25°C, If = 20mA, Vr = 5V
Symbol Min Typ Max
Forward voltage: Vf 3.2V 3.6V
Luminous Intensity Iv 6000mcd 7000mcd
Chromaticity Co-ordinate* x 0.31
Chromaticity Co-ordinate* y 0.32
Reverse current: Ir 100µA
Viewing angle: 20°
*Please refer to CIE 1931 chromaticity diagram
Click to expand...

I understand very little of this, except that they operate on 3.6v max(?:eek::confused:).

Can anyone tell me how I'd go about wiring 6 of these (in series?:confused:)) from a molex connector?
 
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d_brennen said:
Thanks, that looks like it could come in handy. Don't want a pre made as I said though, just a wee project and to learn something.
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The main reason I suggested a pre-made solution is to remove the risk of you potentially damaging something (probably your psu) if you do something wrong, like short circuit something.
 
geuben said:
The main reason I suggested a pre-made solution is to remove the risk of you potentially damaging something (probably your psu) if you do something wrong, like short circuit something.
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I know where you're coming from and I wasn't trying to be rude/arrogant! ;)

By the looks of your sig you know a thing or two about electronics? What other kind of power source do you reckon I could use? Was trying to avoid using batteries for obvious reasons...
 
d_brennen said:
I know where you're coming from and I wasn't trying to be rude/arrogant! ;)

By the looks of your sig you know a thing or two about electronics? What other kind of power source do you reckon I could use? Was trying to avoid using batteries for obvious reasons...
Click to expand...

Using the Molex connectors is fine, you just might want to try it out a spare old psu first (seeing you come across as a novice in this field).

If your interested in doing a bit more than just having plain lights, like flashing lights (in programmable patterns) or colour changing lights, I'm more than happy to discuss nice novice friendly methods of doing so that would also introduce you to the world of microcontrollers so you can make more mini projects in the future :p
 
Should have said before, I have lots of spare PSUs about my workshop to mess about with. I did some electronics in college but for the life of me I can't remember the math behind LED circuits.

Wouldn't mind being able to make the LEDs "pulse" like a heart beat though ;)
 
d_brennen said:
Should have said before, I have lots of spare PSUs about my workshop to mess about with. I did some electronics in college but for the life of me I can't remember the math behind LED circuits.

Wouldn't mind being able to make the LEDs "pulse" like a heart beat though ;)
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Ah in that case then, use the link I gave you along with the datasheet to work out the correct resistor value for optimum current and the number of LEDs you want in series and go for it.

To make them pulse like a heart beat its probably possible to do that with some simple circuit, can't think what that would be off the top of my head though.

if you wanted to do a bit more with them you can use a microcontroller, one I would recommend is the Arduino www.arduino.cc it comes in a nice little package with everything you need and the programming language is really simple. With one you could easily make your heart beat in about 5mins. You could also add extra modes and have them control able by a button or something. It runs off usb and has regulators and limiters to keep it all safe. You would probably need to find a USB header to USB B cable to mount it internally from a spare USB header on your motherboard, or loop a usb cable back inside. It can be powered from a DC jack too, so I guess you could power it directly from a molex connector (with a modded cable), but then you wouldn't have the communication to the pc.
 
Excellent stuff geuben! I might even have a go at making one of those Arduino boards myself (eventually)!

Riiiiight, is this correct:

The LEDs I mentioned above, for example:

Absolute maximum ratings: Ta = 25°C
Power dissipation: 108mW
Peak forward current: 100mA
Continuous forward current: 30mA
Derating factor: 0.4mA/°C
Reverse voltage: 5V
Operating temperature: -25 to +85°C
Storage temperature: -35 to +100°C
Soldering temperature: 260°C / 5secs
Absolute optical characteristics:
Ta = 25°C, If = 20mA, Vr = 5V
Symbol Min Typ
Forward voltage: Vf 3.2V Max 3.6V
Luminous Intensity Iv 6000mcd 7000mcd
Chromaticity Co-ordinate* x 0.31
Chromaticity Co-ordinate* y 0.32
Reverse current: Ir 100µA
Viewing angle: 20°
Click to expand...

So, these have a voltage requirement of 3.6 max (do I use the max figure or the nominal? Also, is this the "voltage drop" across one of these components?) and a forward current of 30milliamps (this is the LED current, yes?).

So... the calculator gives me this for 3 in series -

Supply = 12v
Voltage Drop Across LED = 3.2v
Desired LED Current = 30 milliamps

=

Nearest higher rated 10% resistor = 82 Ohm
Safe pick is a resistor with power rating of = 0.12 Watts

Is this right? It says that from a 12v source any more than 3 won't work? This can't be right is it?

Sorry for the massive convoluted post lol
 
3.2v does seem a little high, but they might be very bright LEDs.

using a 12v source I would probably run 4 in series as 3 would give a voltage drop of 4 over each, which is outside of the rated maximum. That doesn't limit you to 4 LEDs per molex though, you can run sets of 4 in parallel.

Edit: Ignore that bit about 4 instead of 3.

Edit 2: this link is better http://led.linear1.org/led.wiz it can create LED arrays for you
 
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geuben said:
3
Edit: Ignore that bit about 4 instead of 3.
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Why's that? With 4 they'd be under the rated spec by a bit and would not need a resistor? I am hoping they are very bright lol

Also, this will sound daft to you, how would I run more than one set of LEDs (in series) so that the sets would run parallel? :confused:

Thanks for all the help too!
 
d_brennen said:
Why's that? With 4 they'd be under the rated spec by a bit and would not need a resistor? I am hoping they are very bright lol

Also, this will sound daft to you, how would I run more than one set of LEDs (in series) so that the sets would run parallel? :confused:

Thanks for all the help too!
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Yeah sorry it's late, I got confused. That second link I just posted will show you how to create an array, put in 12v supply, 3.2v drop 30mA and say 12 or 15 LEDs.
 
Cool, thanks.

Now, the molex plug consists of

Color Function

Yellow +12 V
Black Ground
Black Ground
Red +5 V

Where to start without blowing the PSU? Can't be as simple as the +12v >LED array>one of the GNDs?
 
Fantastic gueben. Can't wait to get in to work tomorrow (am self employed so can dilly dally ;))

Going to put together a test array tomorrow I think. One last thing for tonight (I promise!) how do I go about running several arrays in parallel?

Is it just a matter of running say 4 wires from a terminal block on both the +12 and GND to each of the array?
 
d_brennen said:
Fantastic gueben. Can't wait to get in to work tomorrow (am self employed so can dilly dally ;))

Going to put together a test array tomorrow I think. One last thing for tonight (I promise!) how do I go about running several arrays in parallel?

Is it just a matter of running say 4 wires from a terminal block on both the +12 and GND to each of the array?
Click to expand...

Yep, it's that simple. Just remember to wire the LEDs the correct way around and you shouldn't have any problems. When you come to make the bits you actually want to put in your case I recommend you get some heatshrink, it's hides your nasty soldering and makes it much easier to avoid short circuits.
 
555 timer curcuit

you could use a 555 timer curcuit to get flashing LED's and sequence LED's. Also, these curcuits can be found on google and often have ranges between 5v and 15v, should be right about what you need. personally id link a timing curcuit up to a series of logic gates each with a mosfet or set of relays to trigger a light curcuit. this way it is easilly expandable and you don't have to worry about power issues as much for the LED's

could i also suggest you use a voltage splitter curcuit? this would reduce the voltage down to an acceptable level for your LED's to be powered by and then you could use transistor diode logic to get em to flash.

on a side note, look up the RS flip flop curcuit, it might give you some ideas in what you could do...
 
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