The PCB (Christmas) Tree (#P32)
Epiphany has already passed and St. Knut’s day is next Wednesday, it’s about time to stop being lazy and get the Christmas tree out of the living room.
Well, yes, but not the usual way. As shown previously, it’s not an ordinary tree. It’s green and it has fancy little lights all around, but it’s also containing significant amounts of lead and it needs a PoE port to operate.
Meet the PCB Tree.
Made from scrap circuit boards, random bits of wire, leaded solder and a couple of Chinese ingredients, it’s a wonderful Christmas abomination that sat the entire last year in my office and received a significant addition in early December 2020.
It’s actually difficult to make nice, festive photos, since it only pops with the lights on, but that certainly exceeds the dynamic range of my camera. Please forgive any asymmetry – it’s been grown into that shape naturally
Here’s a quick list of AliExpress goodies that were needed to make this happen:
“100pcs LED Diod 5mm RGB Blink Slow Flash Diffused Light Emitting Diode Rainbow 2Pins Lamp Red Green Blue RGB Flashing 5mm LED” – those are slow, (self-)color-changing RGB LEDs that will do from around 2.8V to 3.5V. Voltage on mine is currently a tad too low as the blue drops significantly in brightness, but pink really shines. 2.64€ per package of 100pcs, first bag bought back in August 2018.
“Cdycam 3pcs/1bag PoE Splitter Power Over Ethernet 48V to 12V IEEE802.3af Standard Type 15W Power Supply Module For NonPoe Camera” is a cheap yet perfectly fine PoE adapter that delivers enough juice to the tree. I removed it from the case and cut off the non-PoE cable (still wish these were installed the other way round). Then it’s just mounted as one of many PCBs and delivers 12V to the inner DC-DC converter. 8.56€ for a pack of three units in June 2020.
“DC DC Step Down Power Module 5-16V To 1.25V/1.5V/1.8V/2.5V/3.3V/5V Universal Adjustable Buck Voltage Converter Board 3A For LCD” – these are excellent DC-DC converter boards with adjustable output, dirt cheap yet reliable. Based on the MP1495 chip from Monolithic Power (ACSG marking). Says 3 amps, might do 3 amps, I’m using around half of that on the tree. It’s set to 3.3V and has a sub-10Ω resistor and a 1.6A glass fuse in series to the massive amount of paralleled LEDs. Originally 0.87€ a pop in March 2018, lately less than half that amount with a little bit of postage on top.
Everything else was scrap PCBs, some wiring (mostly from Cat.5 cables, solid core), 60-40ish solder and I would guess about 40 to 50 hours of work.
Speaking of PCBs, there’s a reason there’s no in-depth shots of all levels aside from my soldering, hot snot, sawing and drilling misdeeds to make them all fit together: Especially the top part and the core is made from prototypes, scrapped (unpopulated) and outdated PCBs from my employer. While one wouldn’t be able to reverse-engineer that stuff from a couple of photos of abused boards, I’m not exactly eager to offer more detail than needed. After the 2020 expansion, the bulk of the tree however is made from scrapped commercial PCBs, there’s literally laptops in there, projectors, SAS backplanes and midplanes, routers, access points, switches, IoT gateways, solder practising boards for sparkie apprentices, you name it.
One part of making all the boards work together nicely is killing active stuff on there when using existing power traces. Most, but not all of the boards, use the ground plane for, well, ground connections, but there’s a plethora of ways to connect the positive side of the LEDs. When using power rails e.g. on routers to make all existing LEDs light up, one is often also powering a significant amount of other ICs that drive up power consumption. For one of the bottom levels, I had to literally eject magic smoke from a dozen chips against all protection measures (hehe) with my 60V lab power supply. In the end, that level dropped from 2.5W to 0.3W. I don’t need any rogue ARM cores in there…
Total consumption is around 5.5 to 7.0W according to the PoE power meter that has not yet been featured here. That’s about right as I do have a comparison with a regular 9 to 12V supply on the DC-DC board. PoE was chosen for three reasons: 1) Of course I will fucking sneak in a working PCB that supplies the entire thing, 2) Standard 500mA/2.5W USB will no longer do the job and someone could accidentally plug this into such a socket, 3) It’s a convenient thing to do at work when every appliance with a power cord needs to be tested, even if you are literally the guy that can and will do the testing. With PoE, the power supply is already provided by the IT guys and I’m just plugging into a free outlet. Same thing at home, as I do have an 8 port PoE switch available. That one, by the way, was part of a large packet of Amazon scraps/returns that not only yielded a second and third working PoE switch after minor repairs, but also added quite a few dead PCBs to the tree. See Construction fails in networking gear (#R9) for reference
About the general asymmetry: This is, aside from my lack of planning, a result of using various PCBs without cutting them to size. There are a few boards that I split, e.g. a SAS board that was just too long but also too narrow to fit a level far below, but most are in one piece, some completely unharmed and mounted with thick strands of copper or by wedging them between others. I did a small reconstruction of the crown as it was getting a bit wobbly -the top was never intended to grow to that size, so it was built too flimsy and would not carry the weight of the entire tree when picked up from above. After all, this bad boy is about 3.2kg now…
The overall shape didn’t change with this reconstructive surgery, though. For all extensions I just minded the envelope and filled parts where needed. The tree is screwed together in approximately the middle but would need the base plate desoldered and three holes drilled (screwdriver through the bottom layer) before it can be opened again. For all major joints it never was an option to make them dead center – instead all of those connections had to be placed where PCB holes, large ground planes or simply enough PCB material on both sides were available. The entire thing is balanced, but the bottom stand isn’t centered. Doesn’t really matter all that much, it does look somewhat symmetrical when considering the lights:
There’s slightly over 100 over those fading LEDs built in, plus I’d guess around 30 more static LEDs from the original PCBs. Some of those status LEDs do have a limiting resistor, others really suck up some current. I think there’s single gallium phosphide LEDs in there that do gulp 40mA which can also be seen on thermal images. The fading LEDs are placed everywhere, from capacitor spots to PCB mounting holes and in every available port. There’s LEDs in VGA and audio jacks, and across LAN transformers that had their case yanked off.
Well, before handing over to more mundane blog posts in 2021, let’s just celebrate this high-end turd with some more video:
Original 29 minute version, until my RX100M2 hit the FAT32 file size limit for the complete file (sheesh…2021!) even though it only stores this as 2GB chunks in internal memory. Furthermore, it’s a total pain in the ass when the manual settings in both manual modes are automatically reset by some wizardry that totally knows better – and then defocuses, changes shutter speed or f-number. Fuck you, Sony, it’s a great camera but that really sucks.