Thursday, June 19, 2014

Blackshadow flashlight mod

Now that my MELD drivers are up and running, I've decided it's unacceptable to have anything less than full functionality on every light, so I've been going through and modding everything to have RGBWUV. The Blackshadow Queen is one of my favorite hosts for its size/form factor and the reflector that throws better than anything else in my collection.

This mod uses MELD firmware so the UI matches my other lights, but because it runs on rechargeable cells only I used linear regulators instead of the full MELD driver. This also allows me to run much higher current on the white LED. 

To fit all the LEDs in the reflector aperture, I have my MELD LED boards, including this XP variant. They are FR4 though, so it wasn't going to have good enough thermal conductivity for my main emitter. To solve this, I came up with this PCB sandwich arrangement. 

The first step was to slice the PCB to make it thinner. The epoxy that holds the fiberglass layers together weakens when it's hot, so I set up the heat gun to get this bare PCB really hot and then sliced the top layer off with a blade. 

Next I cut out the space for the white XP-sized part until it fit perfectly over an XP-L. After the hole was cut, I reflowed the red, green, blue, and UV emitters on to their pads. 

I then reflowed an XP-L onto a star (this happened to be a weird star that included spots for other components, I only chose it because I wanted a thicker-than-standard star). The thin PCB holding the colors was then epoxied down around the XP-L using Arctic Silver. This picture is during the electrical test after epoxy.

On to the host: I disassembled everything, including punching the brass ring out and separating it from the stock driver. 

I reuse the the daughter board that holds 6 AMC7135 regulators for my white LED. For connections and mechanics, I reuse the main PCB, but all the components need to be stripped off first. The only one I left was the tantalum input capacitor.

I wired up the LED board using 30AWG for colors and 24AWG for the white. All the solder connections need to be made as low-profile as possible, and then they are covered in kapton tape to prevent shorting against the reflector.

I then put the LED board into the head using thermal grease. There's enough trimmed off of the star to allow it to move around a bit to get perfect centering. 

Here's what it looks like after the reflector and lens are assembled. It was a bit tough to center--I had to push on the back of the star through one of the wiring holes to hold it in place as I tightened down the reflector. After a few attempts I hit the center.

On to the driver. The board in the center of this picture is cut out of a PCB I salvaged from the scrap bin--the only thing it holds is the microcontroller (PIC16F1825) and a decoupling capacitor. The only reason I used it was to save me from making connections directly to the QFN-16 part. Ideally I'd use a SOIC part for this, but I didn't have any on hand at the time. The part on the right side is a 6-pin 50mil pitch female connector, which is used for programming and so is connected to the ICSP points on the microcontroller.

The stock daughter board holds 6 regulators and is used to drive the white LED. Branching off of that I have 4 more AMC7135s for each of the colors, wired independently. These are wired free-form, but they have their grounds soldered to a fairly thick ground wire which keeps them mechanically stable.

At this point I programmed the microcontroller so I could do full hardware tests as soon as the LEDs were wired. This required a simple harness to adapt the 1x5 0.1 header on the PICkit3 to the 2x3 0.05 header in the driver. The female connector is epoxied flush in a hole cut into the main PCB.

Here's a picture of all the electronics wired up, undergoing final electrical test. Before I stuffed everything into the cavity, I wrapped all the exposed parts in kapton tape to prevent shorts.

Here's what the head looks like after the board is pressed in. The programming connector came out pretty clean, and it does't interfere with the batteries since they only contact the outer ring.

Here's a final shot of all the emitters turned on at minimum. The UV isn't on; it appears green because of a neat refraction effect in the XP-L dome. This light runs the same firmware as my MELD2 drivers, but with a few options that optimize it for linear drivers. There's a full video and description of the user interface in my post about the most recent MELD firmware update