One of the things I dabble with every now and then is electronic circuitry. I’m not nearly to the point of doing fun things with PIC boards and microcontrollers, but I do enjoy wiring up and playing with small circuits. And I’m currently somewhat fascinated with what one can do nowadays with LEDs.
I’ve ordered an MR16 light from SuperBrightLEDs — I got the 3W warm white spotlight bulb. It’s actually quite nice; I have some MR16 track light transformers I’m not using, one of which seems to work OK (no flicker or buzzing) with this bulb. The light given off is remarkably similar in color temperature to a nice halogen bulb, and reasonably bright — you’d need a few of them to come close to a 20W halogen bulb — more than I expected. It’s actually quite good as an accent/spot light. Unfortunately, it’s $35 per bulb, which isn’t cheap.
So I started investigating the parts. They use Philips’ Luxeon LED emitters from LumiLeds, which come in various configs. The ones I’m interested in are warm white (1W max — the 3W bulb uses three), and cool white (3W max). They’re like other LEDs except they’re much brighter, and use correspondingly more current (350mA instead of 20mA like normal LEDs).
I had the idea that I could put together a simple package of an LED and the support circuitry, and with any luck fit it all into a package that would go into a bi-pin Malibu light fixture, so I could purchase some reasonably inexpensive outdoor lighting, and add way more lights to my piddly 120W transformer (that’s already got 50-60W in use with 5 fixtures) for various bits of landscape lighting.
So I ordered 5 of the cool white 3W LEDs, which came out to about $27 for all of them, and have those. I ordered the star package which includes a bit of a heat sink; these things get hot.
For a support circuit, I didn’t want to use the traditional “just use a resistor” circuit to limit the current. I found the LED current controller circuit that uses a couple of resistors and a transistor to achieve the right current through the LED.
I guesstimated some of the values, and ordered five each of the following from Mouser Electronics:
| Component | Price |
|---|---|
| Xicon 3W 5% Small Metal Oxide Resistors, 30 ohms | $0.39 each |
| Xicon 3W 5% Small Metal Oxide Resistors, 2.2 ohms | $0.39 each |
| Fairchild Small Signal Transistors TO-92 BC63916 NPN GP AMP | $0.14 each |
| Rectron Rectifiers - Bridge RS-1 1A 200V | $0.46 each |
The total order comes out to about $7, not including shipping. This is why I’m posting; other than the exotic LEDs, getting components like this can be super cheap. If this works the way I think it should, I’ll have converted malibu halogen lights to LEDs for about $7.50 plus labor; not much more than the cost of the actual replacement bulbs.
If it works out, I’ll post a how-to with pictures. For now, gotta wait till the order comes through.
