Ten pounds of lasers in a five pound bag: PoE projector
A while back, I bought the guts of a projector from polishedball. I pondered for a bit as to what to do with it, and eventually decided to go through with an idea I had a while back: build a single-cable projector, powered entirely over Ethernet.
PoE has been around for ages, but baseline standard PoE only gives a measly 12 watts at the device - nowhere near enough. Fortunately there were some increasingly non-standard extensions that turn the limit up. The highest power option is "Power over HDbaseT", PoH, which Microsemi would like to pretend isn't just their own thing... in any case injectors and device chipsets are readily available, so PoH it was. I found some parts on Digi-Key and set to work. (Later this year, 802.3bt is expected to be standardized, so maybe it'll be that next time!)
Power-over-ethernet devices are basically all the same: power is taken from center taps of the Ethernet isolation transformer and then fed through a pair of bridge rectifiers (so crossover cables don't blow anything up). That gives 48 volts, more or less (PoH ups it to 57v), which is then converted down to whatever the application needs. The power topology of the laser is a little more complicated. First, I used an off-the-shelf "8th-brick" style DC/DC converter module to convert down to 12 volts. That powers the galvo driver, Ether Dream, and a set of three more DC/DC converters producing 5.0, 6.5, and 6.5 volts respectively - for red, green, and blue. Using a switching power supply to get as close as possible to the diode voltage is win-win: it makes the most of my limited power budget, and reduces the amount of heat from the diode drivers. I designed a custom board to do it all and sent it off to OSH Park.
First light came last June:
Nice, but not portable. It needed a case. Eventually I found a cute little box on eBay, designed for audio amplifiers - a challenging 3.5" x 6" x 10", with one side made entirely of heatsink. They're still around if you search for "unilateral heatsink aluminum case". Unfortunately, the existing layout wouldn't fit in those dimensions. Redesign time!
I wound up keeping the optical path almost identical, just moving the telescope on the other side of the bounce mirror. Here it is on the new baseplate:
And with photons coming out the front:
At this point, life got in the way for a while, but I finally got around to ordering a new back panel from FrontPanelExpress and buttoning it all up. Here it is! There's a little color bleed through the spatial filter, but it's not too obtrusive in person. Gotta figure out how to get that pinhole just right.
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