The Power Box
When I describe my rig, there's the PC and what I call the external components which at this moment is the camera, the various conversion boxes and the splitter. They're considered external because they're all on the far end of the SDI cable that is connected to the rig. This page is to describe the power box - the item I use to feed power to the external components.
The Power Box came into being after a number of problems occurred. First, there was the issue that all my external components used the same power plug - a 5.5x2.1 barrel connector - but they didn't all use the same voltage. Most were 5V, some were 9V and some were 12V. Mixing them up will at best result a not-working situation, at worst the magic smoke emits. The solution was to either ensure that each voltage had its own, incompatible connector so mistakes could not be made, or to standardize on 1 voltage for everything. Given that multiple voltages also meant multiple power units, and reducing the bulk of the rig is an important factor, I went with having all external components be 5V. It also allowed me to just bring a stack of 5V power units so I would have spares if I needed them. Next came the issue of needing to find a power source where I needed it. Particularly for the camera this became problematic because it was often placed somewhere in the room where there wouldn't be a power source in the direct vacinity. That meant bringing a long power cable and distribution box on the end. That and the power units were, again, bulk that I'd prefer to get rid of. The proverbial straw that broke the camel's back came when someone needed to charge their phone, and decided to just unplug this power cable, which went unnoticed for a while because the camera had an internal battery and nobody checks the HDMI to SDI converter box to see if it's still powered on. When it's plugged in, that's simply assumed. Clearly a change was needed here.
Since all these external components didn't require a lot of power - the typical power unit was rated for 1 amp, so max 5W per component - I decided to try and feed the devices power straight from the main PC's PSU. The PSU can deliver 5V at considerable amperage. More than 10A was nothing special. So I constructed a 10m cable and connected a converter to the PSU. Power light came on, so that worked. Then I connected a source to make the converter work and it instantly went off. The problem was that as soon as the converter actually had to do
something, its power draw increased. The formula for voltage drop is Vdrop = IR where I is the amps and R is the resistance of the cable - the thinner the cable to higher the resistance and my cable wasn't particularly thick. By increasing I when making the device do something the voltage drop increased and the device quickly found itself underpowered.
So I went with the 12V line and a DC-DC converter on the far end of the cable to convert whatever's left of the provided power to 5V. Going with 12V had the benefit of lowering the amps that would need to be sent over the line, meaning less voltage drop over distance, and the DC-DC converters you can get for next to nothing on AliExpress were cable of dealing with FAR higher voltages. Since I had multiple components I connected a 1-to-4 barrel splitter to the output connector. One important
thing to note is that you should measure the output voltage and adjust it until it provides 5V. In my experience these things, new, are set to dish out what you put into them, which will damage your components. Get a cheap multimeter and set them to anywhere between 5 and 5.25V to ensure they can cope with any power drop resulting from the power drain of all the connected components.
After seeing this work well I simply cut off the input plug from this splitter and connected it straight to the converter board. Next I needed something to connect multiple lengths of this power line in much the same way as I was doing with the SDI cable. Initially I went with simply a thinner version of the barrel connector, specifically 2.35x0.7 which worked okay. It was sufficiently incompatible with the other connectors, but the thin plug never gave me much confidence. It probably felt more fragile than it actually was. It worked well for a number of cons, then at one conference the heat created by the DC-DC converter made the socket expand so much that the plug fell out. It was quickly replaced (redundnancy matters!). At the next conference, literally the day after, all cables to the stage were run down the center of the walking path for the attendees. They would be taped down, but it made me uncomfortable - if anybody stepped on the plugs and it bent the wrong way, the connection might get severed. That didn't happen, but I started looking for a more reliable connector. That became the GX12-2. Here's a pic of the two, separate and connected:
Naturally having a DC-DC power converter just bare, out in the open is A Bad Idea™ so I initially looked for a purchaseable box that would fit something this small while also being able to vent out the produced heat. Not finding anything that fit the bill, I decided to fabricate them myself using the 3D Printer at my hackerspace, Hack42
. I installed OpenSCAD, learned the language and quickly made a box that did what I wanted. In the first version of the box the board within still had considerable space to move around, there was a hole for the output cable on one side and a larger hole for the barrel socket on the other. The venting slits had the added benefit of allowing you to see the board LED inside so you could easily see it was powered. When the box failed because the plug lost connection with the socket due to heat buildup we were recording in a very overpopulated room that got so warm even the projector started to complain of overheating. The board got so warm the 3D printed box's base warped. This led me to the current design, in which the board is enclosed snugly within the box. There is NO room for movement within. This also meant that, by volume, there was less hot air within the box which I believe also helps with venting the heat out. The transistor is the bit that actually gets warm, so I found some tiny aluminium heatsinks on AliExpress and glued one on using thermal epoxy. Finally the GX12-2 connector is now outside of the box. It wasn't required, but the sheer size of the socket made it sensible. The final design became this:
Each rig comes with 3 of them because even though they've proven quite reliable, these power boxes can and do fail. In the year since I've started using them I had it happen once.
My OpenSCAD file for a box with rounded corners
and the OpenSCAD file for the vented power box and its lid
. To use, simply place both files in the same directory, then open the second one with OpenSCAD. I tried commenting it a bit but I'll admit the computations aren't particularly neat.