What type of LED's for a LED clock...

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I'm still thinking of building a round LED clock with 12 pcb's that are sections of a larger ring. My question has to do with the type of LED's to use:

1. Diffused vs clear?
2. Viewing angle?
3. Output type (standard, medium, high ?)

I was thinking of using 5mm through hole round ones. The clock diameter will be around 15" and the width of the ring 1.75".

I plan to use PWM to dim the clock depending on ambient light, but ideally it should look the same brightness from any angle. Does that mean I want the widest viewing angle possible? What is the importance of the viewing angle when using diffused?

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Diffused LEDs always have a fairly large viewing angle. Being a clock I'd think viewing angle is quite important, so you certainly do no want LEDs with 5 degrees of view angle. The clock will be unreadable from anything but dead front and then you get blinded.

I'd use high output types, they will use less current for the same amount of light. You can always dim them if they prove to be too bright.

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Agreed with what JJ said. I'll second the importance of the high-brightness LEDs. By the sounds of it you'll be using a lot of LEDs - their combined current draw can quickly and easily become quite staggering. Using high-brightness LEDs can really help keep total current down, which helps you everywhere, from power supplies to output drivers to PCB trace thicknesses, etc.

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Thanks guys, I will have 192 leds total. 12 hour markers, 60 hour, 60 minute, 60 second.

What defines a high output one? I was looking at digikey, but I don't see a category for output type...

Thanks,

Alan

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For LEDs I'd recommend ebay - much better prices than Digikey, Mouser, etc. Also, they'll all be high-output types on ebay.

Wide angle LEDs are usually short and have a flat (or nearly flat) top.

Get some LEDs and experiment with a diffusing a few to compare the results. Lots of people use sandpaper to diffuse them, but I recommend a dremel tool with a course buffing wheel like this:
http://www.ebay.com/itm/36pc-POL...

That will diffuse an LED in a few seconds.

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Sounds like you'll only have 4 on at a time, so current shouldn't be a big problem. Unless, of course, you want to run it from a coin cell.

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Torby wrote:
Sounds like you'll only have 4 on at a time, so current shouldn't be a big problem. Unless, of course, you want to run it from a coin cell.

Under normal conditions this will be true, but I plan to have lots of fun making animations and other cool effects so I'm going to design it to allow all LED's to be on at one time.

I ordered some LED's from eBay so we'll see how much light they put out vs how much current they consume. I found a pretty neat shift register at Digikey that can handle quite a bit of current in case I need to have more current - TPIC6C596N. Looking forward to getting the LED's in so I can see how much power it takes to make them look good...

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You can still use pulse width modulation to drive the LED's, such that they all appear to be on, but you're actually turning them on and off so fast that the human eye sees them on all the time. Stagger the pulse so you turn one on, then off, the next next pulse goes on, then off etc. This will reduce your current consumption from 192 to maybe 12 at a time, or maybe 8.