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  #61  
Old 04-30-2012, 01:23 PM
chrischrischris chrischrischris is offline
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Hi elec_mech.

Pin 3 & 8 of the display going to Vcc to half current makes sense. I've amended my drawing. However the C.A. displays only have 1 Vcc connection (connected to each segment) - so no problems.

The BCD in my timer schematic - correct, it was a mistake - built correctly, drawn incorrectly. I still need to rename components to numbers (i.e. R1, R2, C1, etc). Will do that soon.
Count down timer PCB_V6.pdf
PS. the BCD is still connected in the circuit to give full flexibility to change the count down time to something odd. I was looking at placing it somewhere water proof on the score board for people to access.

The blue syran wrap (we call cellophane) - will try it. Your absolutely right - I can imagine it will make a huge difference because the white of the displays won't be seen.

Higher voltage supply - yes, I will try it out.

Making my own digits if all else fails - yes, I tried already into perspex - cracks really easily. I did buy 100 leds of various colours and strengths already. I arranged some to make a digit and it worked, however my power supply couldn't handle it at the time. I even have 15000mcd leds - I'm "sure" they would be bright enough. It's just time to build. I see how I go.

As for the Vcc and current measurements (thanks for detailed explanation of how to measure), results are:

24.04 regulated power supply
Resistors = 7.5Ω
(C.A to segment / ULN to resis / ULN earth to ULN outputs / total Vcc)
a = 22.39v / 0.66v / 0.78v = 23.88
b = 22.36v / 0.68v / 0.78v = 23.82
c = 22.38v / 0.66v / 0.78v = 23.82
d = 21.68v / 1.27v / 0.76v = 23.81
e = 21.60v / 1.35v / 0.76v = 23.81
f = 22.50v / 0.60v / 0.78v = 23.88
g = 22.44v / 0.62v / 0.78v = 23.84
Average = 23.84.

Currents:
a=85mA, b=88mA, c=86mA, d=158mA, e=170mA, f=79mA, g=82mA.
Total = 748mA1 (Av 106mA).

Not sure why "d" and "e" go so bright. Obviously need larger resistors to compensate.

So from above, please correct me if I'm wrong:
a. Voltage supply of 24.04V "just covers it, but a bit higher would be safer
b. Adjust resistors with new supply to reach say 25mA per led (i.e. 25x5 per segment.
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  #62  
Old 04-30-2012, 08:54 PM
elec_mech elec_mech is online now
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Quote:
PS. the BCD is still connected in the circuit to give full flexibility to change the count down time to something odd. I was looking at placing it somewhere water proof on the score board for people to access.
You could get clever and just use a fast and slow clock to set the time via the remote. That way they don't "touch" the circuit or expose it to the elements (of course, the BCD switches could be moved off the board to alieve this concern). If you leave everything the same and allow the user to change the BCD settings, then they also change the results of your 25, 30, 35, and 40 minute settings. Up to you though.
Quote:
24.04 regulated power supply Resistors = 7.5Ω (C.A to segment / ULN to resis / ULN earth to ULN outputs / total Vcc) a = 22.39v / 0.66v / 0.78v = 23.88 b = 22.36v / 0.68v / 0.78v = 23.82 c = 22.38v / 0.66v / 0.78v = 23.82 d = 21.68v / 1.27v / 0.76v = 23.81 e = 21.60v / 1.35v / 0.76v = 23.81 f = 22.50v / 0.60v / 0.78v = 23.88 g = 22.44v / 0.62v / 0.78v = 23.84 Average = 23.84. Currents: a=85mA, b=88mA, c=86mA, d=158mA, e=170mA, f=79mA, g=82mA. Total = 748mA1 (Av 106mA). Not sure why "d" and "e" go so bright. Obviously need larger resistors to compensate.
Hmm, first, it's odd that d and e are taking more current. Let's check a few things first: 1) Are d and e noticeably brighter? 2) Does this hold true for all/most of your digits or just the one you measured? 3) Pull each resistor out (one side will work) from your circuit and check the resistance. You could have a couple of bad resistors or at least two that are far enough different from the others to make a difference. I assume you're using 5% tolerance resistors? 4) If the resistors are all about the same values, try replacing the ULN2003 with a new one. Any difference? 5) Failing 3) and 4), try switching the LED digit for another one. Any difference? It could be the LED segments in which case your only option is to either use a different resistor value or replace the digit entirely. My point being you shouldn't have to use a unique resistor value for every segment in the same digit. I hope the problem is with the resistors or ULN2003. I'd be concerned if it was the LEDs in the digit (who knows what problems it will have in the future?). Bill might have some input on this as well.
Quote:
So from above, please correct me if I'm wrong: a. Voltage supply of 24.04V "just covers it, but a bit higher would be safer b. Adjust resistors with new supply to reach say 25mA per led (i.e. 25x5 per segment.
I'd definitely go with a larger voltage supply. I read a nice response on this subject from Bill sometime earlier this year on another post. He might have some info on this in his blog on LEDs. And yes, the 25mA supply per LED strip sounds like a good approach to see if they'll be bright enough for your application. Before implementing these, I'd suggest locking in the size you need the digits first, then brightness. You may well find you don't need much more in the way of voltage or current with what you already have. Hate to see you spend a lot of time or money on this to find out you need a different display altogether with different requirements. This comes from personal experience.
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  #63  
Old 05-01-2012, 03:19 AM
chrischrischris chrischrischris is offline
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Hi elec_mech.

I thought of the fast/slow from the remote, but though I would keep it simple as it would be rarely used.

The bright segments - yes, they are brighter. I think it's faulty. I did try another display and I "think" it also was a bit all over the place. I'll check again tonight and let you know.

I'll also print out a 12", 16", and 20" display and see how it looks from a distance. Still waiting on buying blue celephane to see how that goes. I'll get back to you soon.
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  #64  
Old 05-02-2012, 10:05 AM
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Bill_Marsden Bill_Marsden is offline
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I would like to see that myself. Finding colored plastic is always a problem for displays. All the hardware stores in my area likes to sell is transparant acrylic. There is supposed to be a local plastics house that sells other colors, but I have not found them yet.

I take it you have decided blue is more visible in daylight?
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  #65  
Old 05-02-2012, 11:25 AM
chrischrischris chrischrischris is offline
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Hi Bill.
I did by some "blue" cellophane (we call it). I need to test it in daylight now - it was raining and dark all day.

I did google for the plastic elec_mech suggested and there are some places that have it.

Ultra blue - now that seems to be a bit of a problem. I've asked someone who deals with colour and they say our eyes don't pick up bright blue so clearly at night. Damn. To add, the 8" are a bit too small.

I looked up a supplier in china today that sold led signs you see at petrol (gas) stations. They are red however, but 16" or 20" (see attached file).
PE-AZR.pdf
These are made of LEDs that are 4000mcd. They run on a 12V DC supply and and a 30A supply can handle 24 units so they say. They come with their own light dimming circuitry (which was another thing I was considering). I asked if I could adapt them to use on my scoreboard and their "engineer" said no - however the english translation the whole time was a little ordinary.

On one hand I want a pre-manufactured unit that is bright enough. On the other hand making a digit isn't rocket science, but teadious. But it means repairs would be easy - just replace some leds. So I'm still deliberating which way to go. I'll experiment more on the weekend (at least with the 10" units I have and the blue plastic - that I'll buy).

Mech_elec - I verified 3 of the segments on the 8" digits draw higher current - brighter with same resistor. This happens on 2 of the 4 I've got. The supplier says to just to use different resistors. This is fine, but what happens one day if someone has to change the digit? They would have to balance again with different resistors - hmmmmm.
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  #66  
Old 05-02-2012, 08:23 PM
elec_mech elec_mech is online now
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Quote:
Ultra blue - now that seems to be a bit of a problem. I've asked someone who deals with colour and they say our eyes don't pick up bright blue so clearly at night. Damn. To add, the 8" are a bit too small.
Bah, if you get into the science of it, our eyes pick up green the best and red is ideal for night time because our eyes, for lack of a better description, don't need to adjust as much. There is a much more scientific explanation, but I don't know what it is offhand. Do note that red lights are used in darkrooms without ruining the film and most alarm clocks use red LEDs for a reason.

In the end, you really just need to try it out in your application and see what you think. As Bill inferred, blue LED displays are well-suited for daylight reading applications, but that doesn't mean they won't work for night applications. Besides, blue is cool and you'll be the envy of, well, other home scoreboard makers.

Quote:
These are made of LEDs that are 4000mcd. They run on a 12V DC supply and and a 30A supply can handle 24 units so they say. They come with their own light dimming circuitry (which was another thing I was considering). I asked if I could adapt them to use on my scoreboard and their "engineer" said no - however the english translation the whole time was a little ordinary.
I think you could make these work, but I'd insist on a schematic or more detailed installation/users guide. The attached sheet is not enough.

Quote:
On one hand I want a pre-manufactured unit that is bright enough. On the other hand making a digit isn't rocket science, but teadious. But it means repairs would be easy - just replace some leds. So I'm still deliberating which way to go. I'll experiment more on the weekend (at least with the 10" units I have and the blue plastic - that I'll buy).
I think your biggest hurdle is making sure the digits are big enough. Once you determine the needed size the question then becomes a) can you find a pre-made 7-segment digit in the size you need and b) if yes to a), what do you value more: having it done for you and buying the right power supplies or building your own and having more control over the power supply? For some people this is determined by cost, for others their time.

Quote:
I verified 3 of the segments on the 8" digits draw higher current - brighter with same resistor. This happens on 2 of the 4 I've got. The supplier says to just to use different resistors. This is fine, but what happens one day if someone has to change the digit? They would have to balance again with different resistors - hmmmmm.
I wouldn't worry too much about the life cycle. If you were designing a product for the market, this is worthwhile concern now. Since you're doing it for your soccer team, I think you're okay as long as you document this or find better made digits. Alternately, you could keep the resistors on the board all the same and add a few to the digit itself. Anyone replacing it, assuming they're electrically-minded, will see this when they replace it, although adding a note made with a Sharpie would be good too. Just a thought.

Bill, check out Tap Plastics. They're in the NW somewhere, but they're prices and selection are fairly good and I've done a lot of looking. I had one place locally that sold colored acrylic, but they went out of business and I haven't located another one here either.
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  #67  
Old 05-03-2012, 03:11 AM
chrischrischris chrischrischris is offline
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Thank elec_mech.

Good point on the night clocks being red, but yes, if they were blue, we would have the coolest board around

More schematics on the gas station price led signs - I was thinking exactly the same today. I'll ask.

Today I've printed out in B&W a 10", 12", 16" and 20" of a single digit. I'll bring it to the soccer ground and check it out. If I can make it out from a distance, then it's just intensity and blue cover acrylic I'll need to consider (well at least with the 10").

Extra resistors on the digit - what a great idea.
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  #68  
Old 05-03-2012, 06:08 AM
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I think you will find blue works just fine. The thing about red LEDs, is they don't involve all the cones (the color sensors) of the eyes, at least that is my take.

Did you see the digits on my plans? They were 1 foot tall, and could easily be scaled up. My concept was to drill holes in plywood (which was painted after the holes were drilled), then press fit high intensity LEDs into the wood. The plastic over the LEDs would tend to disperse the light, which would be needed.

If you are interested in persuing this let me know. Once you have the LED drivers it is easy.
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  #69  
Old 05-04-2012, 06:05 PM
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Chris, what size digits do you need. I have some ideas I would like to run by you if you are interested. I was thinking about them on my way home from work.
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  #70  
Old 05-04-2012, 10:58 PM
chrischrischris chrischrischris is offline
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Hi Bill.
I've printed up 8", 10", 12", 16" and 20" in B&W. I was going to bring it to the soccer ground tomorrow morning to see which suits. My gut feeling at this moment is 16" is the best, however I might get away with 12". I've been shopping around.

1. "Betlux" large digits: http://www.betlux.com/product/LED_se...BL-SE1600A.PDF
I was given the spec sheet last night. 30 day lead time for ordering. Have asked to verify peak voltage and current because I can't work it out from the spec sheet. Also the mcd. I believe what I need is between 4000 and 5000. The supplier however had said red, orange and green is suitable in the sun. Waiting on price.

2. Shenzhen Yuhong Electronics Co.,Ltd
http://yuhongled.en.alibaba.com/prod...time&edm_ver=e
This unit was gauranteed to be bright enough for outdoors. Specifically for scoreboards, etc. Costs around $85USD per unit. Bit high.

3. Same company - another sales man sent me a spec sheet for a digit he also said would be bright enough. I think the price was around $30.

I priced yesterday an 8' x 4' piece of black 3mm acrylic - $110AUS. Probably double the size of sheet I need. This could be laser cut (dots only for the led wires to poke through). The "dividers" could be also laser cut, but this might end up costing too much, so maybe just a cover. This would would cost around $150 per 8'x4' (polycarbonate - for when they kick the ball into the sign). LEDs - either staw hat or flat top seem best. They have about 110 viewing angle. However, the cost of all this may end up costing close to buying the units.

I did string up two old laptop power supplies last night (19.5V, 6.9A) and connected 11 leds in series (4 sets in parallel) with resistors. Looked ok. I'll string up a 12" digit to see how it looks tomorrow. But I'm still bending towards bought units if I can find them.

One other thing I didn't consider yet, i dimming the lights at night - otherwise I'll probably blind everyone. Not sure how to do that yet. Can I address the anode of each segment with a resistor via a light sensor?

So digit size that would be "prefered" is 16". Still got to check if 12" however ok for temperature and time. But have to weight this also against stocking different sizes and different voltages, etc. More than happy for any suggestions.

Last edited by chrischrischris; 05-04-2012 at 11:04 PM.
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