EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: roleroz on January 15, 2023, 06:02:15 am
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I've been working lately on a full robotics system for my son to use with Lego (they killed Mindstorms :( ), and now I'm thinking about lighting. I see that a lot of people use pre-wired 0402 or 0603 leds with a through hole resistor encased in shrink wrap in one of the leads, and that is all well and good, but I would like to know if there are SMD leds (specifically 0402 or 0603) that have an integrated resistor, so I can connect them directly to 3.3V or 5V and not burn everything down
I started thinking about this when my daughter asked me if we could put Christmas lights on the roof line of some Lego houses we have, and that would either need a ton of cables with their own resistors, or putting them in parallel in one continuous string with the resistors in the string itself, so having tiny leds with the resistors integrated would be awesome
If that's not possible, I've been thinking about soldering a resistor to the back of the led, but I would need some kind of insulation between the other 2 terminals, which would otherwise be touching
Open to any and all ideas ;)
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I am not aware of any LEDs with built-in resistors in such small packages, unfortunately. Some ideas for homebrew LED/resistor arrangements:
For christmas lights, you could wire a handful of LEDs is series and run them off 12V with a single series resistor -- and also just a single wire running between the LEDs, rather than a pair for parallel wiring.
To make your own little packages of an SMD LED plus SMD resistor, you could try to place them side by side, joined by the single solder joint in the middle. Not a whole lot of mechanical strength, but it should work. You could add some clear heatshrink tubing once all connections are made, for mechanical support and electrical insulation.
If you want to mount LED and resistor back to back, as you described, Kapton tape would be a simple and compact way to insulate the two terminals. It is a thin adhesive tape that withstands soldering temperatures, and is often used in electronics. Kapton is the best-known brand name; the generic material is polyimide.
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Here you may find integrated resistor SMD LEDs: https://www.ledtronics.com/Products/ProductsDetails.aspx?WP=549 (https://www.ledtronics.com/Products/ProductsDetails.aspx?WP=549)
Normal 5mm integrated-resistor LEDs are available at Sparkfun, Alliexpress etc. But could not find the SMD ones anywhere else.
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There are LED strip lights with 12 volt repeating every three LEDs They are used for under cabinet lighting and I have use them for illuminating meters etc in radios.
These might be too big or too bright for your application though.
https://www.ebay.com/itm/125386874986?epid=24044098585&hash=item1d31a3e06a:g:NZUAAOSwJ5Nit2Y0&amdata=enc%3AAQAHAAAAwA2B9fC8PXdxsNhEGfQyOr7LDbyzUe6QPqisgLKfwk1ju2uzU%2F7Sik5VkOQtvF%2Bmg5PbJQXR%2FL0fRf6tPRV8iQgqtHXkPHEzGDxHfZDzSWwKPeSMOPrKLENnOBhUKwxuVyEnXqfyBNMBBw7rWcriw85vujNYyQXJ7BOYhQlKlNlNYj55qdygpTCjpY6bned8RR0CPH1C6CJgRa6uAnU1p%2FaJ4QAF6owfxxDE27rIY%2B%2BDeL%2FcMDBPGxQRduBZFgwRSg%3D%3D%7Ctkp%3ABlBMUNS3tKG4YQ (https://www.ebay.com/itm/125386874986?epid=24044098585&hash=item1d31a3e06a:g:NZUAAOSwJ5Nit2Y0&amdata=enc%3AAQAHAAAAwA2B9fC8PXdxsNhEGfQyOr7LDbyzUe6QPqisgLKfwk1ju2uzU%2F7Sik5VkOQtvF%2Bmg5PbJQXR%2FL0fRf6tPRV8iQgqtHXkPHEzGDxHfZDzSWwKPeSMOPrKLENnOBhUKwxuVyEnXqfyBNMBBw7rWcriw85vujNYyQXJ7BOYhQlKlNlNYj55qdygpTCjpY6bned8RR0CPH1C6CJgRa6uAnU1p%2FaJ4QAF6owfxxDE27rIY%2B%2BDeL%2FcMDBPGxQRduBZFgwRSg%3D%3D%7Ctkp%3ABlBMUNS3tKG4YQ)
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It's possible they exist but I've never seen one. You can get some really small through hole resistors though, much smaller than the common 1/4W variety.
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WS2812 or equivalent? These are addressable LEDs which need a data signal fed to them, alongside a power and ground rail. They come as pre-made strips, or can be bought as inidividual units and each wired to power, ground and a data line. You'd need a microcontroller to supply the data line with a signal to turn them all to whichever colour you'd want, or do fancier things like flashing or colour changing. The data line is shared by all the LEDs, so only three wires for the whole system. Much pricier than typical LEDs though.
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The WS2812 is surface mount but I wouldn't call it "small". Perhaps though we should get an idea of what the OP actually means here. 603, 805 and 1206 are the most common SMD LED sizes, a 1206 is about the size of the head of a pin, the others are smaller.
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The OP has mentioned 0603 and 0402 as the sizes he is thinking of; much smaller than the integrated WS2812.
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WS2812 is 5mm square but the same thing exists in smaller packages, eg https://www.adafruit.com/product/4684 (https://www.adafruit.com/product/4684) and https://www.lcsc.com/product-detail/Light-Emitting-Diodes-LED_OPSCO-Optoelectronics-SK6805-EC15_C2890035.html (https://www.lcsc.com/product-detail/Light-Emitting-Diodes-LED_OPSCO-Optoelectronics-SK6805-EC15_C2890035.html)
However you then need to pass 2 power leads and a data lead down the string. A serial connection of 10 leds could be run off 24V with only a single wire.
You can buy 3mm and 5mm LEDs with an integral resistor (eg https://docs.rs-online.com/e88a/0900766b81384f0d.pdf (https://docs.rs-online.com/e88a/0900766b81384f0d.pdf)) but I haven't seen those in SMD sizes. I think the chain of LEDs, a higher voltage, and a single resistor for the chain is the most compact solution.