Intro
Ahhhh LEDs….don’t we love them? Today there is a huge variety of them. But there is one type I particularly like. These 5 mm RGB diffused LEDs, easily available from various sources and quite cheap (amazon.de, aliexpress, ebay etc).
Here’s why I like them
- They are super bright. According to some datasheet which may or may not be what you are buying from less reputable sources, the green LED peaks at 5000 mcd at 20 mA. Your typical, cheap diffused green LED is usually under 100 mcd. So it can be 50 times brighter or more.
- They are dirt cheap. Right now you can have a pack of 100 for as little as $3-4 or 3 cents each from ebay. They are so cheap that I pretty much gave up using red, green or blue LEDs where I need that and use one of these, cutting the unused pins.
- They are efficient. Unlike bulbs, LEDs can light proportionally to the current down to very very low level. Forget driving them at 20mA, it’s enough to drive them at 1 mA and they will be visible. This makes them awesome where battery power is required.
What I do with them
I use these a lot, most times not bothering with red, green or blue LEDs where panel mount is concerned. Just use one of the color, they are cheap enough for small scale and it’s easier to keep one type instead of 3. But that is not novel, however here are a couple of cool applications you can use them for.
Orientation LED
LED throwies are a simple concept: connect one LED to a coin cell battery with some glue and it will light for quite a while. Use it for decoration or art. The coin cell battery can only supply a limited amount of current which is usually safe for the LED and the non linear nature means that it will work for a few days even weeks before dying off.
I made a small adaptation. Remember how I mentioned the RGB LEDs are very efficient and their brightness scales with current? Well, I added a resistor to limit the current. With around 10µA I can get 2-3 years of operation from a coin cell while the LED is normally visible even in typical home daylight (excluding sun).
About two and a half years ago, I built this guy.
One LED, an 82 kΩ resistor and a CR2032 battery. Used some tape to hold it together.
Sleeping in a totally dark room? this thing is just the right amount of smallness and brightness to provide an orientation point so you can move when you wake up during night…if you are the king of person who can orient based on that.
Why the rust? After about 1 year of operation, I moved to a new place. It was one of the las thing to take and I put it in a pocket which resulted in a trip through a washing cycle. Afterwards I cleaned it a bit and it worked for about another year. So 2 years on a coin cell.
I just rebuilt the device on the day I am posting this, let’s see how long it lasts without a wash cycle.
Update 15.02.2022 – the battery is now done – after lasting 34 months, almost 3 full years. Time for a replacement.
Visible remotes
Remember my home automation project that I am not posting much about lately? (Yeah, my priorities have shifted a bit). Remote controls and buttons are an important thing. Smartphone control is cool, but I want buttons here and there too.
The cool thing is that such LEDs can be used to provide an indication during the dark of where the button is. Reality works so nice, that considering the typical 10-20 kΩ pull up/down resistor from inside the micro i use, I can just connect the LED across one of the buttons, with no extra resistor.
This will result in a higher LED current, maybe in the order of 50 µA. This is not a problem, AA or AAA batteries will still provide years of light and the brighter LED will be better visible. Here is one installed in a prototype round remote, the LED is just below the battery.
From the outside, the remote looks like this, with the LED visible in normal home illumination through the cracks.
Conclusion or something
Ditch dedicated red, green or blue 5 mm LEDs for hobby, these are the only ones you need. They are bright, which means you can use them at lower current. They will work for years of indication on a battery powered device.
I could not find similar LEDs in 3 mm or SMD packages, if you know please share.
Update: It’s been done in 3mm!
Sorta. The leads and base are still in 5mm form, but the dome has been shrunk down to 3mm. So looks like my theory is correct.
https://www.ebay.com/itm/192267520191
Oh, wow. Those are expensive. They look like shaved down 5mm ones.
I hadn’t considered using cheap RGB LEDs to replace all other LEDs. Thanks for the tip.
Probably don’t see 3 mm versions because it’s too small to easily get four leads out of the package. Plenty of “flashing” 3 mm RGB two-lead LEDs, though. Maybe need some microscopic hacking of those. 😉
Yes, that is true. 4 leads would be unfeasible in that package. But I would not mind having a 3 or 2 pin bi-color one in a 3mm package that is as efficient as the 5 mm version. But I have not found one.
I don’t think hacking the flashy ones is interesting. But there are 3mm, 3 pin bi-color LEDs. If they had some sort of digital protocol over a single wire like the WS2812 that could be interesting. But again, they have to be very efficient.