In other news, the bottom panels for the fireplace surround are done and tested. Lee Clark and his assassin’s gaze missed out on unlocking the “working til 3am with soldering irons and hot glue” achievement. But I hear he was waylaid by a prior engagement that looked better than we did; besides, this is probably not the only opportunity.
Also missing from the mix last night was Zen Master Zack, the imperturbable Namibian from Wisconsin and his simultaneously soothing and maddening calm. But there’s no time for introductions here; I’ll get to it later. In the meantime, Caleb and I soldiered onward.
I have learned a metric ton of how not to mount these little beasts, including hot melt glue being a relatively unforgiving adhesive, more searingly painful to touch than superglue, and only slightly less sticky for your fingers. And soldering irons heated to 750°F only have to graze you to leave a painful burn.
I’m still in awe at the capacity for the Heroic Robotics PixelPusher to drive so many of these LEDs in unison with minimal fuss and bother. You do have to check EVERY SINGLE SOLDER JOINT both to insure data continuity from one string to the next, as well as avoiding bridging power and data lines when doing the insane-looking but efficient and darned clever wiring technique that Lee mentioned during the previous work session. I look forward to perfecting it on the very last panel.
Basically it looks like you are soldering a bare wire across all of the strips’ contacts simultaneously, but it actually just involves a ridiculous amount of stripping wire insulation in the middle of the wire itself, no mean feat for stranded copper conductors. You see, when laying down LED strips in rows or columns, you usually want the data to travel in a chain from first pixel to last in that chain. This ends up with some strips pointing one direction while its neighbors are pointing the opposite way. And you will recall with LED strips that the power signals (+5v and ground) are on the outside edges of the strip, while whatever data and clock signals are in the middle. The net effect us that you end up with these arrangements where the ground and 5 volt power rails (as such) face each other from one row to the next, meaning the power feed conductor can be bare wire in the gap between strips because there’s nothing to short against and it’s a whole lot faster to lay down.
And why do you lay down power lines this way? Well, gentle reader, if we just fed power on one end and chained it from the end of one row into the next, the voltage at the end of 430 pixels wouldn’t be strong enough to light them at all. That, and the first pixels in the string would melt from the amount if current needed to drive the whole string.
Oh, and don’t forget to size your power supplies for the worst-case power draw. We pretty much cooked one of the cheap power supplies by leaving a display up with all pixels fully lit. Turns out that you can overdrive the power supplies for short periods before the switch circuitry starts to melt down. Who knew? Full marks for Caleb and his quick hands and shouting “SMOKE! SMOKE!” a couple times before pulling the plug.
The net effect is that I need to go back and verify the power draw. I may have to dig out my ammeter, or just go buy another one at Harbor Freight.
Damn, these things are bright.