Bit more soldering

Soldered three more pillars yesterday, and did another eight tonight. On average it takes around 11 minutes to solder one pillar. Not bad. Only 2 mistakes in the last batch: one LED was inserted into the jig incorrectly (or I marked the wrong lead) and one bad solder joint.

Here's the result of my labor so far:

24 done, 40 more to go.

Stackable!

Received a bunch of spacers today (HTS-310) and they fit the cathode boards perfectly.

The whole construction feels pretty solid, very little flex. That's a good thing, since putting in the cables requires quite a bit of force. Speaking of cables, that's one more extra time consuming job...

Not much time spent on the cube lately. I'll probably be able to find a couple of free hours this weekend (yay for second Easter day). I did spend some time on some other stuf.

Cathode board works!

And we have a video!

Pretty neat! I found a bug in my bit angle modulation code which caused some weird things. After I fixed that everything worked like a charm.
My setup is like this:

• An Arduino Nano on the left side of the breadboard, this microcontroller has a bit of animation code and it streams the resulting led states (on or off for each LED) to the cathode board. It does this roughly 12.000 times per second, creating a very smooth image. It's important to note that it is streaming the data for a full 8x8x8 RGB cube, but only one row of the top level is is shown (since that's the last byte that is streamed). On other words, the same smoothness can be achieved when the complete cube is connected. It's also interesting to note that this code is capable of streaming 100 "frames" per second and has loads of cpu power left.
• The Arduino is connected to my cathode control board using a ribbon cable. Each of the five wires in the cable is connected directly to one of the pins of the shift register on the cathode board for full control. There's a three wire power cable as well; one wire for logic power supply, one for logic ground and a separate one for LED ground. Finally there's an eight wire ribbon cable connected to the cathodes of the LEDs on the breadboard.
• The 8 LEDs on the right side of the breadboard have their anodes connected directly to 5V. The green cathodes go to the cathode control board which contains a series resistor for each LED. The other end of each resistor is connected to the collector of a transistor. The emitter of each transistor is connected to the LED ground pin on the board, and the base goes through a series resistor to an output pin of the shift register. If the output pin goes high, then current can flow through the transistor and the LED goes on. If the output pin is low then current is blocked and the LED goes off.

Next up: two more boards for full RGB control :)

Testing the cathode board

Quick update, more will follow.
I've been a bit busy with some other stuff lately, I had to make 35 buzzer games (like this one) for a group of kids, so I spent most of my free time last week putting a bunch of leds, resistors, battery holders and piezo buzzers together. The rest of my time went to miscellaneous stuff like housekeeping and filling in my tax forms. Last night I finally had some time to get back to the cube...

I need some way to test if my cathode boards work after I solder all parts on them, so I populated a breadboard with 8 LEDs and wired them to the cathode board and an Arduino. The Arduino runs pretty much the same code as the cube will eventually in terms of refresh rate and how the cathode board is controlled. It took some time before I had everything working somewhat correctly, always double check your connections and don't mix up the MOSI and MISO pins...

But in the end, it works! One LED didn't light up, I didn't solder the transistor for that one correctly, easy fix. I'm still tweaking the code a bit, there's a bug somewhere that stops the brightness from functioning properly. I don't have any photos or videos at the moment, I'll shoot them after I fix that bug.

One thing that I overlooked is how bright a 0603 LED can be. I have a small power indicator LED on the board and that thing is just blindingly bright. I've already replaced the 150 Ohm series resistor with a 1K Ohm, but it's still too bright. I'll try a 10K tonight; all it needs to do is provide a visual indication, not light up the living room...