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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@DrAzzy
Purpose:
To act as a desk and project lamp, where the color temperature can be adjusted ranging from a very cool white, to very warm white, and the brightness can be varied. It will be controlled by a free-standing Espruino, and capable of loading “preset” colors, as well as adjusting the color channels individually. Additionally, the controller will display current temperature and humidity.
I decided to use 1 and 3W luxeon clones (commonly called LED beads) for the lighting, in 5 channels. All LEDs used are phosphor based, even the yellow.
Hardware:
The hardware can be broken down into 4 parts:
The Arm: The first problem was to obtain an articulating arm that can clamp to the table and hold the light head in the desired location. Luckily, I had vintage-1960’s flourescent desk lamp, which I gutted, and removed the head from, and then ran 6-conductor wire down it. Tricky wire running job, as there are also springs and straps inside the arm. The base of the arm has sufficient space for the MOSFETs and and resistors, and a terminal strip at the back (removable) for easy maintenance.
The Head: The LEDs must be mounted on a heatsink to avoid burning out. The heatsink used here was about 4”x3.5”, obtained from one of the audio amplifiers from an old projection screen TV (these are readily available for free on classifieds/freecycle/craigslist, at least in the US - worth scrapping for the huge fresnel lens, trapazoidal (often front surface) mirror, speakers (sell on ebay), and some heatsinks).
I soldered the positive side of all the LEDs together, and thermal-epoxied them to the heatsink. This way sucked, and I recommend epoxying all the LEDs down in the right pattern first, and then connecting to them. And being more careful so the frame isn't at +5 volts. For running the 1W and 3W white LEDs off the same voltage, a 0.68 ohm resistor was necessary in series with the 1W LEDs.
The heatsink is screwed onto the backing plate (which is in turn affixed to the arm using the same mount that was used for the original lighting head). To allow the head to be removed for maintenance, the LEDs are connected to a pair of 3 wire terminal strips on the head backing plate. Finally, the shroud is affixed using 4 screws (not installed in above picture).
Design and planning regarding the diffuser mounting system is ongoing; presently, I am using a somewhat rudimentary mounting system as shown in the main picture.
LED drivers: The ballast resistors and MOSFET driver board are located in the base of the arm. The ballast resistor values are low (1.3, 2.8 and 3 ohms), and have to be picked fairly close to the targeted value to get full brightness from all channels without exceeding the manufacturers’ specifications*.
The board itself was prepared from single-sided copper-clad board from Amazon, using the Toner Transfer method. Design and layout was done in Eagle. The board in there now was created using HP Advanced Photo Paper; it sucks, don’t use it. I got better results with the front cover of Bloomberg BusinessWeek, though (I didn’t use those because I was expecting to have more trouble than I did drilling the holes; this was a practice run. - but this one turned out okay, so I figured I might as well use it). I have dextrin-coated paper in the mail for next time I make boards.
The MOSFETs are DMN2075-U's, rated for 4.2A continuous at 2.5v on the gate.
Controller: Espruino, with a PCD8544 screen (on SPI2, shared with micro SD card), 4x4 matrix keypad, and a DHT22 temperature and humidity sensor.
I plan to add a BMP180 pressure sensor, and switch the keypad out for a 4x5 unit, which will enable a richer UI.
Pink only on!
Colors don't come out so well in photos. I'm not entirely happy with the warm whites, though - they don't seem as warm as I'd like them to be. Investigations are ongoing.
*Or what I believe to be their specifications - datasheets for the Luxeon clones seem non-existent. There are dozens of distinct and different LEDs, many of which are not copies of actual Luxeon LEDs (colors are available which Lumileds never sold), but rather similar 1W LEDs in the same package. If data sheets exist, the clueless vendors don't seem to know about them. Note also that the ebay vendors don’t know the specs either, and, if pressed, they are won’t to provide inaccurate specs.