First project - need help

[davenc]

Hi!

I have a project in mind, but don't have much knowledge or experience with what I need to do. I hope I can explain this so that it makes sense.

What I hope to do is create "light panels" using translucent plexiglass and LED's. I would like to have the ability to power them from a single power supply (or at least multiple power supplies connected through one on/off switch) and also have the ability to dim the LED's (again all panels on one dimmer switch).

I expect each panel to have between 3-5 LED's as the panel sizes will vary. I also expect some of the panels may be separated from each other by several feet. I am looking at 3mm LED's as I need a small physical size.

In trying to research this before asking, I have the impression that I could run the LED's in each panel in series and then run the panels in parallel (hoping that I can have some type of plug for each panel so that a panel can be replaced if needed).

So, I hope someone can help me figure out (tell me )...

1. What my options for a power source are?
2. What type and how many LED's I can run from the power source?
3. On/Off switch options?
4. Dimmer switch options?
5. Resistors needed?

Thanks! I greatly appreciate any help on this!

Dave

 

[MikeMl]

The electrics are easy. What is hard is how to diffuse the light from the LEDs to uniformly illuminate the panels.

 

[davenc]

Care to elaborate on the easy electronics?

I think I have the diffusion figured out. The LED's will be sandwiched between two pieces of plexi. They'll be glued together and then painted (with several coats). After that, I'll be using a CNC mill to engrave test or art into the panel. I feel pretty confident about this part of the project as I've done several tests. I just need help with the electronic side.

Thanks!

 

[silvermopar]

How many LEDs do you expect to run? What voltage do you want them to be? Will this be something you want to plug into a wall outlet (120V AC) or something you'll run off of batteries? Will it run all the time or just for a few minutes now and then? Leds do not draw much current. I believe you could make this circut a simple as a power input which would be DC to run LED's. I would expect it to be be a 12, 9, 6, or 3 volt supply. I believe you could use something like a toggel switch to control power and perhaps a "pot" to control the voltage reaching your leds thus making them bright or dim.

 

[Sceadwian]

Your options for a power source are as unlimited as your completely unspecified series string =) You've provided us no details so we can't provide you with any. How many LEDS in series do you have in mind, 3, 4, or 5? How many panels do you need to run in parallel? We don't know where you're deriving your power from, if this is a battery or mains powered device, what are the voltages you have available to drive from.

Throw us a bone =)

 

[davenc]

At this point, I am not certain on the exact number of LED's I'll need as I am still designing the panels. I may have as many as 25 panels and I expect each panel will have 3-5 LED's (panels will be various sizes). So let's say 125 LED's.

I was hoping to either use 120v AC or a 12 PC supply (I've reach that can be used).

Thanks!

 

[davenc]

Throw us a bone =)

Sorry, I am here because I really don't know the answer to those questions yet.

Ideally, I'd like to run this from a 12v PC supply or two with power/dimming to all panels controlled through one toggle and dimmer control. I should have no move than 5 LED's in series for each panel and some panels I expect to only need 3 in series.

Supposing I end up with 25 panels, can I run them all in parallel if I have a total of 125 LED's.

I am really open to suggestions as I don't have any parts yet and I need advice to decide what to order.

Does that info help?

 

[davenc]

Regarding running the panels in parallel or series, I really don't have a need to do it one way or the other. I was just assuming (based on some data I read) that I'd want to run at least some in parallel.

I honestly don't know what I need which explains why I really need help.

 

[Sceadwian]

If you're using a 12 volt source you'll be able to only use about 3 LEDS in series. A rough estimate for a typical bright white LED is 3.5 volts at 20ma of current. So three in series will drop 10.5 volts at 20ma, leaving you 1.5 volts to drop with a resistor, at 20ma ohms law says the resistor needs to be 75ohms, to limit the LED's max current, this is approximate at room temperature, above or bellow room temperature will cause changes. Ideally you want to use a current controlled power supply that can adjust as a diodes forward voltage changes as it heats up pretty dramatically.

 

[davenc]

OK, thanks. I think I need to fabricate one of the larger panels and just see how well 3 LED's will light. That will give me a much better idea of how well my design will work and exactly how many LED's I'll need.

Thanks for all the help so far! I am sure I'll be back with more questions.