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Progress
Here I try to document how the project is going along, because not everything that happens is transparent via the commit log. Newest entries are always on top.
During the last days, I designed LED Driver Module A, based on the A6211 Constant-Current-Driver IC. This has been the hardest part of the development until now, because choosing analog components that need to handle high power under non-trivial circumstances is new to me.
I might need to derive improved versions of this if I made a mistake, and/or I might create more modules like this to test other constant current drivers. The plan is to use the same form factor and pin layout, so that the driver modules are drop-in replacements of each other.
The driver module and the adaptor were ordered today and should arrive in about 8 to 10 days.
The first LED Module that I ordered 8 weeks ago arrived 2 weeks ago, and only now I found some time to test it quickly. Attached to the first prototype lamp, every color channel lights up when it should.
As I said before, it does not fit into the enclosure. I designed an adaptor, that should not only make it fit physically, but also allows a smooth transition from the old pin assignment to the newer one, which is partly implemented on the A2 board and will be fully done on the next version of the main module. The configuration via solder bridges needs some more documentation though.
The adapter has required a surprisingly large design effort. It only routes a few signals, but due to size constraints it needed four layers and I nearly switched to 6 layers.
I've attached the TLC59711 (twelve channel LED controller, but with very low power) to the LED Module C to test the mixing of 10 different LED colors. To make it easier to adjust the colors, I wrote a small adapter program, so that I can use 12 Knobs of an Arturia MiniLAB Mk II to directly control the color channels.
With this, I could roughly test the color rendition of each channel and various mixes thereof, and also fade between monochrome amber and polychrome amber. It's working as expected, but also confirms that it's good to have multiple variants of white LEDs, Amber LEDs and at least one kind of red LEDs.
I also ordered a lot of new parts for the next tests. Need to design one or two additional PCBs to test color mixing with the full power of the LEDs.
I ordered those boards 10 days ago and they already arrived. Looking very nice, the LEDiL connector fits and the lenses/reflectors also fit (but are extremely close to the pin headers).
With these boards I will finally be able to test the CREE XLamp LEDs, and with them, the Constant Current Driver(s).
I tried to reflow-solder the boards using the OpenReflow hot plate, that also arrived today. I don't have a dedicated controller board for it, not even an adjustable power source. My computations showed that a constant 12V drive could be exactly right, so I tried an old PC power supply and it worked perfectly! That's great, now I can reliably reflow-solder at home.
The LED Board C works very well, the colors of the XLamp Element G LEDs are nice, and the color mixing ranges from "wtf" to "99% perfect" depending on which lens I use. Ordering 10 different ones was a good idea!
I could only test with 3W power until now, because I did not adjust the driver board, and because I don't have the heat sink yet. But 3W without heat sink stays very cool, so 15W with heat sink will be no problem as well.
The LED Module A v1.0 finally arrived, six weeks after ordering. As described in #2, my placement of the connector was very unfortunate, and I need to make a small adapter if I want to use them in the exiting enclosure. I already started designing it, and it will also help to bridge the small differences in pin assignment between different LED Modules and different Main Modules.
Finally made an automated testing rig for the TPS92200D1EVM evaluation board. With this, I can test if / how the constant current drive handles the PWM signal it is feeding me.
First results: it's much more complicated than I thought, and the official documentation does not describe it well. I think I could work with this driver, but it would need significant effort in the software to do it correctly. Also, I can't use most external PWM generators with this, because I need to set the exact timings / frequencies and vary them from about 50 Hz for extremely dim light, through 1000 Hz for medium brightness and can only use the desired 3000 Hz above 50% brightness.
Recently I ordered an assortment of reflectors and lenses from LEDiL, and they arrived today. I will need the LED Module C to test them, which I ordered yesterday. I might try to test it with a larger LED, or using try to connect the new, small LEDs without the board, but I guess this just won't work.
The lenses look great, and I start to understand why they aren't cheaper. I couldn't make something link this at home, and I doubt that I can get something similar with professional rapid prototyping either.
I started designing LED Module C. This is going to be interesting. I try to put 25 very small high-power LEDs into a circle of just 2cm diameter, so that they can all shine through a single lens. This will definitely need more than 2 PCB layers, and the thermal management is going to be... interesting.
Today I tested one of the reflectors that I 3d-printed days or weeks ago. It works exceptionally well for the light that is actually reflected, but like every full parabolic reflector, a lot of light just comes out of the LED and goes off without ever having the chance to be reflected.
I will likely need lenses instead of reflectors, or need to test half-bowl reflector designs. My first 2d-simulations of a half-bowl reflector looks promising though.
Met some interesting / interested hackers in Münster's WarpZone. Together we could fix some minor soldering issues on my LED Module A2 prototype that I reflow-soldered in an old kitchen pan on my inductive stove. Also made progress on the software and got a lot of new ideas and feedback.
The PCBs for LED Module A2 arrived, which I ordered after Module A, but because I did not order the Assembly, I already expected them to be here earlier. I hand-placed about 150 SMD components and tested a very hacky soldering process with sand in a pan. It worked very well, though the sand was very dirty and the dirt got burned up and filled the appartment with smelly stuff. Can't recommend, won't do it again.