Rectangular LEDS

I'm thinking of making a Set Theory Clock display for a desk clock and
using LEDs for its display. This needs a selection of rectangular red and
yellow LEDs, both small stackable ones that could be used to make a VU
meter type bar display: 1.5x5mm or (preferably) 3x10mm tops ideal and
some bigger ones: 5x5mm or (preferably)10x10mm tops.
I've just been looking at online catalogues. Maplins and Farnells don't
appear to have anything except round LEDs while RS don't have anything
bigger than 1.5x5mm rectangulars and nobody appears to have them in
yellow.
I remember that these types of LED housings used to be around, so can
anybody suggest where I may be able to get them now?
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Martin Gregorie
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Everything you read in newspapers is absolutely true, except for the  
rare story of which you happen to have first-hand knowledge. ? Erwin Knoll
Reply to
The Natural Philosopher
I got some green 2 x 5 (ish) mm ones the other month, probably from CPC they had a number of different sizes IIRC but possibly not what you specified. 5 mm square might be a boout, nvere seen 10 mm square.
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Cheers 
Dave.
Reply to
Dave Liquorice
How about these?
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Rick
Reply to
rickman
LED-L-113T-Series-29357
That's pretty much what I was looking for, thanks. To clarify: There's a pic of the original. It would be nice to get as close to it in appearance as possible:
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I don't want the flashing light on top, but the rest would make a suitably enigmatic clock displat from a minimum number of components.
Those rectangular LEDS you reference are stackable, so should do nicely for the 5 minute bar and I think the light bars on another page at Rapid should do the trick for the 1/4 day, hour and minute bars.
Thanks.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
Thanks, but as you said, the 5mm square aren't quite big enough for what I need. It looks as though Rapid Electronics do have what I need. They,
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look worth bookmarking: they have stuff the biggies don't bother with and good prices too.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Martin Gregorie
ND/519620
Thanks, for the links, but not quite what I want: I need some bigger blocks (5 x 10 would be good). Rapid electronics, as suggested by TNP do have the bigger bricks as shown on their Light Bar page.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Martin Gregorie
I don't understand. You said you wanted up to 5x5 so I find you 5x5 LEDs. Then you tell me not large enough???
In any event, Digikey has literally thousands of them. Go to their page and search on LED.
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Rick
Reply to
rickman
Apologies if I wasn't clear enough: but I thought I said that fairly clearly that, while I could get by with 5x5 if there was nothing better, I really wanted rectangles.
If you've looked at the link I posted to the Set Theory Clock you'll see that the design needs to have four equal length rows of LEDs and would look pretty unpleasant/amateurish without matching lengths. One row contains 11 tall, thin rectangular LEDs, and the other three rows contain four wide rectangular LEDS each. Due to their relative rarity, the smaller ones set the scale of the whole design and all LEDs need some sort of opaque spacer between adjacent faces to prevent light coming through the unlit LEDs on either side. If the 11 vertical LEDs are 2x5mm and assuming 1.5mm spacers, the basic row is 40x5mm, so the big LEDs should by 10x5mm, Alternatively, if I could get my hands on 11 4x10mm LEDs, then the rows would be 10mm deep and the big LEDS would be 20x10mm.
I just checked DigiKey: the biggest rectangular LEDs they have in both red and yellow are 2.5x5mm and they don't appear to have any red 10x5mm light bars - so far Rapid seem to have them trumped on stuff that's either in stock or that they'll order in. Lots of LEDs and light bar colours and sizes can be specified with their stock filter: not so many are available.
Besides, their search tool is even worse than the Farnell one. I never have liked search tools that need resetting every time you change the criteria and, even worse, when you periodically need to refresh the page just to get the search tool to notice changes. At least the Farnell one always does the expected when you click 'Refresh selection' while the Digikey tool gets stuck with 'Filter' greyed out and 'Reset' the only active option, so you hit it, reinput all your criteria and hope that 'Filter' does something useful this time. It doesn't always.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
Really? I found 20 2mm x 5mm
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(there's 12 more 2.5mm x 5mm)
15 5mm x 5mm:
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10 7.6mm x 7.6mm which are a bit unusually shaped:
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(Onecall is a union of the Farnell and CPC catalogues: if the order code starts with a number it's Farnell, if a letter it's CPC. Unless you have an academic account you have to make separate orders)
The other thing I'd suggest is looking at light pipes, as that can potentially diffuse a smaller LED. Suspect there isn't much call for massive indicator LEDs, because anything bigger is usually for lighting purposes.
Theo
Reply to
Theo Markettos
Why not build up blocks of LEDs to the dimensions you want from smaller ones. I've often done this sort of thing in the past, filing away unwanted plastic to get a snug fit, then once everything is fixed together filing the tops which makes them all the same height and gives additional diffusion.
Wire them in series and feed then from a decent constant current source.
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W J G
Reply to
Folderol
Again I'm not sure what you are looking for compared to what you link to. But it's not my project I don't need to understand.
Your link is to a 5x2 mm LED. Now you say they have larger ones. I think Digikey does too. Here is a search that came up with 50 different red/yellow ones in stock bigger than 5 mm. I found some as large as 19.05mm x 8.89mm.
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I'm sorry you don't care for the Digikey search. I find it to be the best search tool in the business. I think maybe you don't understand how to use it. I have never had to reset anything to start a new search. I just type my new search parameters into the search line at the *top* of the page rather than the *lower* down search which searches within your currently found items. This is actually a *very* useful feature as searches for electronic components are often complex and a single search isn't enough.
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Rick
Reply to
rickman
That's pretty much what I'm planning to do for the 5-minute bar (11 tall, thin LEDs. It will be mostly yellow, but with three red ones corresponding to 15, 30 and 45 minutes past the hour. As I've not seen any multi-coloured light bars, I was always planning to assemble a row of rectangular LEDs with thinner, opaque spacers to stop light from a lit LED shining out through adjacent ones.
Light bars come with either a set of separate segments or with all the LEDs cast in to one coloured diffuser block. I'll use the latter and, as you said, wire them in parallel.
A constant current source sounds good: I understand them because I've made my own for years from a Zener reference, an LM358 driving a transistor whose rating is matched to the required current and a few other passive components. I mostly use them for battery charging at various rates. A NiCd or NiMH pack can be left permanently on charge at a 1% rate when its not being used.
Any suggestions for switches to control individual LEDs or light bars would be gratefully received.
Would a 4050 serve to act as a switch between a constant current source and a set of the LEDs? The 4050 is good for 3-15v operation, so is directly connectable to an RPi. I could obviously assign a constant current source per LED and control them directly, but that sounds like overkill given that it would need 23 CC sources.
In any case, as I want to RPi to do a time-related control job as well as running the Set Theory Clock, I'll need to think about minimising the number of GP pins needed to control the clock so enough are left for the control job.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
Those look like light bars, but no matter: the limiting factor is that I can't find any larger single LEDs with a similar form factor to the 2.5x5 red and yellow rectangular flat-face LEDs with a matching height light bar. Digikey do have a 7x3mm rectangular LED but no light bar or equivalent with a 7x14mm or 7x15mm form factor.
Thats why I'm currently looking at 5x2mm LEDs and 5x10mm light bars: both can be assembled into 40mm long bars with the same 5mm height.
I looked at that page - thanks. I didn't find it, probably because, due to the lack of 10x4mm rectangular LEDs in red and yellow I'd stopped looking for 10x20mm light bars in any colour.
I prefer Farnell's filter to Digikey's and the RS filter is better than either of those. But YMMV, of course!
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
You'll need to wire then in series. Each LED runs at approximately constant voltage, regardless of the current, but the voltages of individual LEDs vary, so in parallel most of the current would go to only some of the LEDs.
In series your current source needs to deliver to a voltage of very approximately 2 volts per series LED.
Combine the switching with the current source.
starting with the logic signal, series resistor to a zener to 0volts. That junction goes to the base of an NPN transistor, which has a resistor from the emitter to 0volts. The zener voltage less 0.7 for the BE junction defines the voltage across the emitter resistor, which therefore defines the current. The LED string goes between the collector and the suitably high voltage supply. Watch the power dissipation in the transistor when choosing components.
If you can't commit 23 pins then I would suggest using a number of latches. 3 8-bit latches would give you 24 outputs, and could be controlled with two address lines, 8 data lines and a strobe, 11 pins in all. 3 write cycles would set them up. 6 4-bit latches would only need 8 pins, but 6 write cycles to set them all up.
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Alan Adams, from Northamptonshire 
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Reply to
Alan Adams
Sounds like a plot. Thanks.
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
Back in the day I was using led arrays for VU meters on cheap disco mixing desks.
I ended up with a very low component count solution which I am trying to remember
ALL the LEDS were in series driven by a current source, and I sorted out the ones not in use with a transistor array - one tranny per LED.
This can be used to switch individual LEDS ion the chain on and off, if you connect the transistor across the LED, or if the transistors are set to a one-of-N type logic array and they are emitter to ground, you can select to short out a whole section of LEDS with the appropriate transistor.
Its not hard to find DIL packs of transistors and simple nand type stuff with CMOS or diodes can serve to turn e.g. a 3 bit signal into a one-to-8 LED bar graph lit.
The big problem is to have enough rail voltage to drive the LEDS in series.
Failing that its one resistor per LED and stick the transistors in series with each LED.
And have a more complex decode.
--
Everything you read in newspapers is absolutely true, except for the  
rare story of which you happen to have first-hand knowledge. ? Erwin Knoll
Reply to
The Natural Philosopher
If doing vu meter try using LM3914 menat for the job if the source is analog and drives LEDs direct, can be cascaded and are cheap.
If driving external latches consider using I2C/SPI 8 or 16 bit ports (latches) simpler wiring and control. Even 74AHC594/5 in series on SPI works as n x 8 bit latches.
make life easier for yourself
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Paul Carpenter          | paul@pcserviceselectronics.co.uk 
    PC Services 
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Reply to
Paul
Yes, I was slowly coming to this conclusion. As has been suggested earlier, a 1 of 4 or 1 of 8 decoder selecting from a bank of latches would reduce the output lines on the RPi quite nicely.
Indeed, and, as it would require at least 8v across the light bars, it probably requires optocouplers in the Pi's output lines.
Not necessarily - I don't forsee any need to separately switch the LEDs in each light bar, so it should be possible to tie the enable lines for all constant current sources for a light bar to a single latch. Or did I miss something here?
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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie
Or: use three 8-bit serial-in, parallel-out shift registers. That only uses 3 GPIO outputs (data, clock, and strobe-to-latch. The shifting-in requires a negligible amount of time.
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-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon
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Michael J. Mahon

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