Custom LED circuitry design help

[Warrenator]

I'm starting a project for a custom Light Board.
I've decided to go with using LEDs under the panel, as they have low power consumption and can be quite bright
and I've never worked with LEDs before, so why not give it a go? And it would be far less fragile and more portable.

Here is my current Panel plan:

LED Panel
---------
Width & Height: 40cm x 30cm
LED type: 5mm White Water/clear (possibly 3mm)


Now. This is where I need the help.
How do I start designing my schematics and working out what I need in the circuit and where?
Should the LEDs be placed in parallel? What resistors will I need?

If I was back in school when I was actually doing these basic ciruits I'd know how. But its been so long, I just cant remember how it goes. =(

Just so you know my level of expereince: I've recently put together some of the electronic 'project packs', so I understand how the basic components work (resistors / capacitors / diodes / transistors). This includes making a 'Fuzebox', which is an open source 8-bit gaming console. But those dont require me to design the circuit, its more or less just building it. I completed a physics course in college and understand electricity quite well.

Is there a standard method for working this out? or a process?

Please help me!

Warrenator

[beer4life]

I'm starting a project for a custom Light Board.
I've decided to go with using LEDs under the panel, as they have low power consumption and can be quite bright
and I've never worked with LEDs before, so why not give it a go? And it would be far less fragile and more portable.
Here is my current Panel plan:
LED Panel
---------
Width & Height: 40cm x 30cm
LED type: 5mm White Water/clear (possibly 3mm)
Now. This is where I need the help.
How do I start designing my schematics and working out what I need in the circuit and where?
Should the LEDs be placed in parallel? What resistors will I need?
If I was back in school when I was actually doing these basic ciruits I'd know how. But its been so long, I just cant remember how it goes. =(
Just so you know my level of expereince: I've recently put together some of the electronic 'project packs', so I understand how the basic components work (resistors / capacitors / diodes / transistors). This includes making a 'Fuzebox', which is an open source 8-bit gaming console. But those dont require me to design the circuit, its more or less just building it. I completed a physics course in college and understand electricity quite well.
Is there a standard method for working this out? or a process?
Please help me!
Warrenator

G'Day Cobber,
Just in case you need a refresher of Ohm's Law, become familiar with this.

First you need to establish the operating current of your leds, typically around 20 ma and the voltage source you intend to use. Let's say 12 Volts.
So to get the series resistor, R = E / I. So R = 12 / (20 / 1000)
So R = 12 / 20 X 1000 = 600. The preferred value above that is 680 Ohms.
It's not a good idea to Parallel the leds as if one fails it puts extra current into the other.

See if that gets you on the right track and feel free to ask for more help as there are many here only too willing.

Kindest Regards, " The Druid ".

[fandtm666]

[SystemRat]

Heres some good info on LEDS and I've bought stuff from this guy before and they are good.

[Warrenator]

Thanks for the quick replies!

Wow, so this is actually going to be far easier than I though. Just a bunch of resistors and LEDs + power supply. I just have to work out the most efficient design to use

It's not a good idea to Parallel the leds as if one fails it puts extra current into the other.

I was just reading that if you have a large quantity of LEDs, it will need high voltage to run if they are all in series (as the voltage drop adds up for each LED). And the best solution is to have a string of series with a current limiting resistor, and place those series in parallel, that way the current required or the voltage required isnt exceptionally high, and the resistors will limit that extra current. Is this correct?

[beer4life]

Thanks for the quick replies!

Wow, so this is actually going to be far easier than I though. Just a bunch of resistors and LEDs + power supply. I just have to work out the most efficient design to use
I was just reading that if you have a large quantity of LEDs, it will need high voltage to run if they are all in series (as the voltage drop adds up for each LED). And the best solution is to have a string of series with a current limiting resistor, and place those series in parallel, that way the current required or the voltage required isnt exceptionally high, and the resistors will limit that extra current. Is this correct?

G'Day,
Yes, that is possible. However you must consider the striking Voltage of the Leds. Typically 2 to 3 Volts, so the more you put in series, the higher voltage PS you will need. Remember if one goes, that string all stop working.
If you have say 10 in parallel and one goes, the current shared by the other 9 is not so bad. You would design your max current to allow for this.
That's what you call design redundancy.
Kindest Regards, " The Druid ".

[Warrenator]

Great!
Now all I have to do is find the right LEDs that I want to use, and I can get to it

I found a great LED calculator that takes your values and builds a circuit based on how your circuit should be like:

I'm not sure how good it would be to copy that exact circuit, but it seems like a fairly good example.
Obviously though I will do what I need to do to make sure the circuit design is good and working.

Now that the circuit schematics seems sorted. Since this is a custom LED Panel and there may be a large quantity of LEDs, from experience would it be better to make a DIY PCB board for this or to get a pre-drilled board and just wire all the components (you know, so it looks like spaghetti from all the wires)? Keeping in mind that this is 40x30cm in size.

[beer4life]

Great!
Now all I have to do is find the right LEDs that I want to use, and I can get to it

I found a great LED calculator that takes your values and builds a circuit based on how your circuit should be like:

I'm not sure how good it would be to copy that exact circuit, but it seems like a fairly good example.
Obviously though I will do what I need to do to make sure the circuit design is good and working.

Now that the circuit schematics seems sorted. Since this is a custom LED Panel and there may be a large quantity of LEDs, from experience would it be better to make a DIY PCB board for this or to get a pre-drilled board and just wire all the components (you know, so it looks like spaghetti from all the wires)? Keeping in mind that this is 40x30cm in size.

Just how many leds do you envisage using?
On a 40 x 30 Cm board you could probably get a 1000 or so?
Have a look at Jaycar:-
CAT. NO. HP9540 /2 /4 (Vero as search term)

These have strip conductors and are pre-drilled. That will save much wiring. You just remove copper strip to adjust the number of connections on each strip.

[Warrenator]

Well, that is what I need to work out.
The one flaw I find with using LEDs is that the viewing angle of the light is not that great (I think).
And because of that, one LED will only light a small portion of the panel. So I need to find out the distance the LED will be from the Panel, using the viewing angle and then work out how far apart I'll need to space the LEDs (and test it).
Unless when the light hits the Panel it desperses across the panel a bit more?

I think I just need to do some quick trial and error stuff to see how this is going to work and get back on this =P.


Thanks for all the help

Warrenator

[Warrenator]

Ok, I decided to actually draw diagram/model designs, and it's looking quite good.
My original estimate of LEDs was WAY off. Ive picked up some large light angle (140°) LEDs, and I should only require 24 at maximum.
There's only two things now in relation to the light box that I require some help with.

1. If my LED panel runs on 12V, is it possible to make it have a power cable that plugs into a power point? Will this be hard to do?

2. I know LEDs don't emit much heat. The panel will be in a small encasing (40cm x 30cm x 5cm .max) and its operation could be of a few hours each use. So will I need to consider any kind of over-heating and use a fan/venting?
If so, will using hard plastic as the case material become a problem?


Thanks for the help so far guys.
This project is becoming a reality

Wazza