LED Color and difused or not - whats the go?

[scorpia]

Guys,

i have been looking around ebay and there seems to be quite a few packs of 1000 LED's between about 6000-10000 brightness.

Most of these seem to be the clear LED type not difused.

the real interesting thing is they seem to be the more expensive colors. ive seen Blue, white, yellow and green.

Im wonderiing how people think that White and Blue LED's will go. Im thinking that blue is not going to be any good as its hard on the eyes.
But white? maybe green or yellow?

Just thinking for something different.

Peter

[Ronp]

red seems to be the cheapest out ....there is a blue made by one of our members thay i think looks nice and isnt to bright on the eyes ether .

I think someone needs to look into what the specs the leds should be difeant colors use more power than the panel was tested for and i dont want to see panels fail due to this...
The original leds used 20ma 1.7v if people start buying other leds that are way beyond the original specs are we going to see lots of leds poping when/if the program locks up (as seen on the ausi video) or will there be controller problems? over heating the chips.

I dont see anyone complaining to much but I wish RJ or others would post/set the limits of the leds that should be used.

[daviddth]

Ron, I thought the Ledtriks was current limited to 20mA per LED, so the voltage is irrelevant. Provided the LED used will illuminate at 20mA and somewhere under 4.5V or so, then the LED's should be fine. Some of the other colors I have looked at have ratings of 30 or 40mA, so they may be the ones that have issues.

Edit: and the program did not lock up - the screen simply did not clear at the end of the display as it was not told to.

[Ronp]

Edit: and the program did not lock up - the screen simply did not clear at the end of the display as it was not told to.
Thats what i was talking about not turning off means the leds are on without being refreshed so they are on full power ... I could be wrong but this is bad...at least
It used to be with the old triks. This is from the original ledtriks post By RJ
Since we are only turning the led’s on for 1/16 the time it takes much more current during that 1/16 to lit them up bright if system hung. Such as your computer locking up etc. the row its on could stay powered and since we are sending more current than the led’s operate on normally while it will not burn them out immediately it could shorten the life of the led’s. I have not had this happen but my computer is very reliable. This is the trade off. The ultimate fix is to add a watchdog circuit monitoring the clock signal and if the clock stops for very long pull the inhibit pin of the 74HC4514 high which would shut all drivers off, no current, no led’s can get cooked, but this was not in the scope of the project at this time.

Like he said 1/16 duty cycle and they were powered with 90 ma to make them brighter
but i may be wrong ...

[RJ]

You are not wrong Ron, the question is this. Is he actually stopping the refresh or not changing the frame. The difference is that they are using a pic to control the refresh like the newer triks. So you can show the frame and be refreshing. If they were not then on this version of the ledtriks it is hard on the Leds. The chips do regulate the current but remember since we are on for 1/16 duty cycle that current if set to 20ma would be averaged to (20ma / 16) = 1.25 ma so the leds will not be bright enough. On the other hand if we crank the regulated current up to say 90ma you would average 5.6ma but most likely fry the leds if it stopped refreshing while displaying anything. So it comes down to a compromise. How did I come to the settings I did? I ordered a number of different leds in the price range I could afford to build them with and fryed them (Ron remember the nights of timing the life of leds and the odd ball one that went almost 2 hrs at 5 times its maximum rating?) to see which ones were the toughest and would hold up the best while giving good light for the current and duty cycle. Then I adjusted the current to match that. There has been many changes by others to the design since then that I am not up on so I can not really help much with led chioces. The current resistor was changed for one I know, which would have a major impact on led life and what would be a good choice. In the end remember this was not a optimum design nor was it intended to be. It was just suppost to be cheap, and be able to be built by most, and display graphics and text. It does that while having its own odd ball limits so it met my goals for it.
RJ

[TimW]

Hi RJ

It sounds like you were instantaneously overdriving the led over a shorter duty cycle to pump the average power back up?
As you described, that would make it risky to leave a row on without a duty cycle present. But I've read it can really turbocharge the brightness if you get the balancing act right.. Did it? Maybe someone who understands the science better than me can talk to this? I guess its not linear.

Looks like the current design has become much more conservative though. - the current control resistor does seem to have pinned it back to 20ma steady state (at least from the datasheet). I guess if noones been complaining this could be why?!

Whats interesting about this is that the brightness is still 'ok'. Is there something going on with perception and POV here? Do our eyes get confused and come up with some crazy nonlinear relationships that make it work? I don't know. Might someone eventually try 'overclocking' it again? Probably. But I'm not encouraging it - The risk is as you say.

Anyway - the Triks-C doesn't stop refreshing, whatever's going on at the PC. So it didn't lock up. If the current issue is still a 'current issue' then I'd probably add another layer of watchdog counter that would usually inhibit the enables if it all went wrong in code. Hasn't been a problem to date - and I haven't considered it yet because of what I think the resistor is doing.

I reckon best not mess with the resistor or current folks - RJ knew what he was doing when he develped this - the resistor probably went in for the rest of us!

Hey, did I mention I'm a big fan of the Ledtriks? Thankyou.

Tim

[daviddth]

My LED's are extremely bright, but I'm not sure if I have the current limiting resistors - I cant remember them being there, but I'll look when I get home

Based on the data sheet, 1K REXT will limit the current to a little under 20mA (470 Ohm is 40mA typical, and although it is not linear, it's close, so doubling the resistance should go close to halving its current)

[RJ]

There is a lot of confusion on the design. I wish the archives were still intact for everyone to catch up on. The protos had no resistors and this is what Ron and I are talking about. The last version of the board that went out as the end product I had John add three 2K resistors as the last change as they still were not bright enough to be daylight readable and there was never a problem with the brightness at night, and the extra bright had risks with it along with causing the directional part of the LEDs to be overstated and so depending on where you stand some would look totally different than others. this helped it some by lowering the power. The LEDs we were using back then were the absolute cheapest LEDs you could imagine and they had a high failure rate so I derated them to try and make sure people had good luck and did not have lots of them failing. The resistors were later changed to 1K by I think john and Phil to bring it up to full rated of the LEDs.

Mine are still running 2k resistors in them and Ron may still have his proto boards that were full current.
hope that clears it up.

I had to think about it a little myself. It has been a long time since I even looked at it.

RJ

[daviddth]

So basically there is no problem with the PC's locking up etc for the majority of people. Most of us are not running the Proto boards, but are running the board with resistors, which negates the issue of overdriving the LED's for long periods. I still might bump the resistance up a little here though

[RJ]

With the 2K or the 1K either one you are in the safe operating zone so it will be fine. Glad you guys are making headway on this. It will really make it much nicer.

RJ