timtheenchanteruk Posted April 11, 2012 Share Posted April 11, 2012 its been a while since I bought semiconductors in any real numbers, for the odd bits, I usually use CPC, I now need to buy myself 3-400 red superbright LEDs, anyone got any suggestions/reccomendations on suppliers, I will be looking at CPC and farnells. Link to comment Share on other sites More sharing options...
Wingwalker Posted April 11, 2012 Share Posted April 11, 2012 The three usual suspects are CPC, Farnell and RS. Why on earth do you need all that lot, Christmas has been and gone :D Link to comment Share on other sites More sharing options...
timsabre Posted April 11, 2012 Share Posted April 11, 2012 The three usual suspects are CPC, Farnell and RS. They are very expensive for large quantities. Are these just bog standard 5mm LEDs? I would recommend you also look at Future Electronics (have a web shop), Plus Opto or Young Electronics (these 2 would probably do pro-forma invoice). Maybe also try Marl. Link to comment Share on other sites More sharing options...
timtheenchanteruk Posted April 11, 2012 Author Share Posted April 11, 2012 Cheers, pro forma not an issue, and that why I was asking, cpc etc are ok for bits etc, but larger quantities are usually better priced elswhere. thanks for those contacts, Ill give them a go. Yes its just standard 5mm LEDs, 2 large letter cutouts, LEDs round the edge, 3 channel so that they can be chased etc, this is going to be fun... Link to comment Share on other sites More sharing options...
J Pearce Posted April 11, 2012 Share Posted April 11, 2012 Bigclive's website recommends phenoptix.com Link to comment Share on other sites More sharing options...
callumb Posted April 11, 2012 Share Posted April 11, 2012 I also recommend phenopix. Link to comment Share on other sites More sharing options...
bigclive Posted April 11, 2012 Share Posted April 11, 2012 Red is an older and more robust technology than the newer green/blue/white technology, so even the cheapest of the cheap red LEDs are pretty reliable. Phenoptix is run by a chap called Ben Gray and his stuff is good cheap generic Chinese import. I particularly love the bright orangey reds round about the 635nm wavelength. A very rich neon-red at surprisingly high intensities. Is your sign going to be viewed directly from the front or from a wide angle range? You can get various beam angles of LEDs including the straw-hat type with a very wide angle because you are viewing the chip directly without a lens. For mounting LEDs on a sign, the basic Chinese "OPEN" signs sometimes just have the LED leads shoved through a single 3mm hole and folded back to hold the LED in place. Alternatively drill a hole that matches the LED diameter and use some hot melt or resin on the back to hold it in place. On a 12v supply you can wire three or four LEDs in series with a single resistor. Link to comment Share on other sites More sharing options...
timtheenchanteruk Posted April 12, 2012 Author Share Posted April 12, 2012 cheers clive, that sounds good, the viewing angle isnt overly wide, approx 55degrees would be the absolute widest (front rows wall to wall) holes are ready drilled, with plenty of glue sticks standing by, I did consider the first option, but the sign is likely to be used in the future, and that didnt seem to give the best mount in tests. Im using a milford instruments LED DMX driver, so was presuming (please correct me here if Im wrong) that I wouldn't need resistors. Link to comment Share on other sites More sharing options...
gyro_gearloose Posted April 12, 2012 Share Posted April 12, 2012 Are you using this LED driver? If so you'll need resistors as the driver provides PWM control, but no current limiting. Have a look at the wiring diagrams on page 2 of the datasheet. To work out the size of the current limiting resistor you use the following formula : (Supply voltage - (LED forward voltage* no. of LEDs))/ LED current in Amps. So for 3 LEDs running off a 12V power supply, where the LED forward voltage is 3.3V and the current is 20mA, we have (12-(3*3.3))/0.02 = 105 Ohms. Note that LED voltage * no. of LEDs must be less than your supply voltage. Link to comment Share on other sites More sharing options...
timsabre Posted April 12, 2012 Share Posted April 12, 2012 cheers clive, that sounds good, the viewing angle isnt overly wide, approx 55degrees would be the absolute widest (front rows wall to wall) 55 degrees is quite wide for a high-brightness LED, they are available but check what you are getting. Most of them are about 20 degrees and if you're off-axis to the sign it will look very dim (had trouble with that before...) Link to comment Share on other sites More sharing options...
timtheenchanteruk Posted April 23, 2012 Author Share Posted April 23, 2012 ok, slight change of plan, the powers that be have decided they want white LEDs gyro, yes that is the driver I am using, and thanks for the formula, Im hoping to get groups of say 6 LEDs in series with each other, then the groups in parallel to make up the sign, Leds in contention arethis one and this one voltage/current are the same for both, but the flat top (probably the one I will be going for) is a wider angle. Link to comment Share on other sites More sharing options...
david.elsbury Posted April 23, 2012 Share Posted April 23, 2012 OT, but I had to laugh at the product info for your first LED - someone's hopefully done a bad copy-paste job :D "Beautiful clear green colour and extremely bright." Link to comment Share on other sites More sharing options...
gyro_gearloose Posted April 24, 2012 Share Posted April 24, 2012 If you want to run the LEDs in sets of six in series you'll need a 24 volt power supply. The combined forward voltage of six LEDs is around 19.8 Volts, so with a 24 Volt power supply you'll need a 210 Ohm current-limiting resistor. If you ran your LEDs in sets of 5 your forward voltage would be 16.5 Volts so you could use an old laptop power supply as these are often around 18 Volts and can supply a reasonable amount of current (around 4 Amps). Also, since they are switch-mode power supplies their output voltage is quite stable, much more so than a transformer-based PSU. Link to comment Share on other sites More sharing options...
timd Posted April 24, 2012 Share Posted April 24, 2012 Also consider using an ATX PSU from a desktop computer. Even to buy new they're not very expensive, and will give virtually limitless current at 12V. Link to comment Share on other sites More sharing options...
lightsource Posted April 26, 2012 Share Posted April 26, 2012 Rapid Electronics http://www.rapidonline.com/Electronic-Components/Optoelectronics Link to comment Share on other sites More sharing options...
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