Hexagon DNA Lamp

Need an idea for a decorative Lamp, or looking for something self-made to give as a gift? Maybe for someone who's a doctor, biologist or bioengineer? Look no further, the Hexagon-DNA-Lamp is here to the rescue!

While DNA-Models like this have been dedicated torture-tests for 3D-printers back in the day, these days' printers can handle such models much more reliable. 

If you want to build a Hexagon-DNA-Lamp yourself (who wouldn't?), then you can just use the model and come up with your own solution to add some light or you roughly follow my guide for assembly and materials. Some (mostly beginner friendly) soldering is required.  However, you can also use the model without any light just as a decorative object, but where's the fun in that?

So pick your favorite color-combination and build youself a unique lamp.

Print Instructions

As with most decorative objects this one as well looks best in PLA. You should choose either a transparent filament or a white one (non-matte-white, because matte PLA is not very "see-through"!). The models from the pictures have been printed in blue and green glow-in-the-dark PLA filament from “redline filament”. “Glow-in-the-dark” is interesting on it's own, because they also glow after turning the lamp off, and they light up in even brighter, different colors under UV-Light. However, use quality filament if you go this route, many glow-in-the-dark-filaments are super-crappy and hard to print, especially on models like this. 

On a DNA like this - especially when printing only one of them - the correct temperature and enough cooling are crucial to prevent upwards-curling of the filament. 

Idealy do a testprint first (use your slicer or meshmixer, so chop off most of the bottom and print the rest, to see if your printer can handle the challenge)! 

You want to go as low with the temperature, as the layer-adhesion allows for. In my case on a Prusa Core-One, I printed with 210°C with rooftop removed and open door while printing at least 2 or 3 Lamps at the same time. just closing the door (even though the roof-panel was not attached) made enough of a difference to have the edges curl up eventually. Even if the print succeeds then, you will have a rough underside which will look ugly. You also don't want to have huge draft-winds going on, because the DNAs would move around like skyscrapers in the wind once the tower gets higher :) . Do yourself a favor and print a testpiece. On modern printers it is very much possible to print these ones perfectly, but it is not a no-brainer. I assume bed-slingers will have a hard time printing this, because the print might resonate alot when beeing thrown around. 

I printed in [email protected] layer height on the default structural profile from prusaslicer.

Besides the DNA, there is a friction-fit bottom-cover as well as two little plugs for the very top. Both of them are optional. If you just want to print the DNA as a decorative object, you can just use the slicer to close up holes in the base. Otherwise the DNA has to be printed with supports for the base-part. Make sure, that the channels of the helix-"posts" are not beeing filled up with support-material, it would be very hard to remove. The posts have round holes going all the way across through the model to be able to sneak flexible filament-LEDs throuth the channels. The two litte plugs can be glued on top afterwards, but this is optional. It would look nice with or without them. I used UV-curing transparent resin to glue the top-pieces in place, which worked perfectly.

You could also use EL-Wire instead of LED-COB-Strips, but I assume they would be less bright.

Materials

When printing the helix as a lamp like intended, you need the following materials:

Don't threat any of the above as set in stone. For a better part I used what i had on hand. I deliberately have choosen linked constant-current-led-driver and stepdown-module, because they are easy to use, widely available and it makes soldering easy, and NOT because it is the best solution. You can use whatever you want to drive the filament LEDs. They all use around ~2.8-3.2V @ ~50-150mAh per 300mm filament (depending on color). I have designed the PCB in a way, that it is very agnostic about the used parts. you can use up to 4 LED-strains, can use up to 2 resistors per strain (in case you are going to exceed the 1/4W these resistors are usually rated for) and can use what you want as stepdown-module as well as constant-current-driver. If you have some experience with electronics, you should at first glimpse immediately see what the PCB is supposed to do: Providing something that is better than free-wiring in the air with hotglue and tape, but not much more. It is not meant to be complicated.

The base configuration is, that you use two of the possible ports to mount flexible filament-LEDs into the DNA-Spines. However, as you have up to four port for attaching available, you can e.G. run another filament around the base on the inside. If the DNA is printed with transparent filament, you most likely can see it even through the base. 

The PCB can of course be used to light up all kinds of printed objects with a hexagonal base, but is designed for this one. 

PCB

I have placed the gerber-files and the associated Kicad-Project in a seperate GitHub-Repo here. However, the first version of this board was made with prototyping-gridstyle PCBs. The circuit is simple enough so that the manufactured PCB is entirely optional.

Getting the PCB

Clone or download the repository-contents. Then zip the folder with the gerber-files (hex-dna-gerber) and upload them to your favorite PCB-Manufacturer. Pick a color you like and place an order. I tested PCBWAY as well as others and they usually cost around $5 (+shipping) for 5-10 PCBs and the quality was absolutely perfect. However, PCBWAY was kind enough, to send some PCBs over to examine their quality. Thank you very much for that. The white ones are from PCBWAY (corrected Version, the purple ones had mirrored power-plug-pinouts). 

Assembling the PCB

There is not very much to assemble here. you can use up to four strains of LEDs and up to two resistors on each. They are in parallel per strand, so use the resistors in pairs with the same values. The Status-LED (D1) and resistor next to it are optional. This is just a status LED. If you want one, and have no Idea what to choose or how to calculate LEDs and resistors, pick a 3mm LED of any color your like, and a resistor somewhere around 80 to 120 Ohms. White LEDs usually work great at 91 Ohms, Red ones are pretty dim at those value, so a resistor around 80 Ohms would be better here. However, every LED is different, and you have to pick a combination that is right for you. If in doubt, start with higher-value resistors. If the resistance is too low, (thus driving the LED with too much Voltage) will burn out the LED over time. The capacitor for good measure is also optional. Otherwise you just need some angled breakaway-pin-headers and sockets. For the 4-Pins I used angled headers and pins, to best utilized the tight space in the electronics-compartment of the DNA. For the 2-pin-headers I used JST-XH-Plugs because they feature reverse-polarity-protection because they are keyed. Everything is just simple through-hole-soldering. Great excercise for beginners.  I also placed 2 Solder-Jumpers onto the PCB, because some stepdowns or constant-current-drivers don't like their “enable”-Pin floating, so you have options for both sub-assemblys to tie that pin to either GND, (it's) VCC or leave it floating . On the LDO6AJSA constant-current-driver, you want to pull the “CE”-Pin high as seen on the images. 

Important Note: Initially I accidentally swapped all 2-Pin-Plugs around so that they are reversed from the usual orientation of 2-Pin JST-XH plugs. However, in the repository and gerber files this is already fixed. With the PCB in hand, you can easily see which is one ground and which is the corresponding VCC, but this is swapped around in most of the pictures. The PCBs you are going to order are in the correct polarity, so you don't have to swap wires if you go for JST-XH also.

For the resistors you need to choose some sane values for your setup. When following this example, your dc-dc-converter should be hard-coded to 3v3. To do this, you have to bridge the corresponding pads on the back, and cut a trace (refer to the instructions of that stepdown module). however, I always found the trace-cutting very annoying, an easier way to to this is to just remove the metal top of the turntable of the adjustable resistor. this has the same effect, it cuts the same line, just slightly later down the road. just break away the metal ring of the stepdown, and use the 3v3-solderbridge. Don't skip this step, if the variable resistor line is not cut, the board will put out to whatever the turning knob is set to, and most likely will fry the rest of the electronics, because the voltage is too high. Use a multimeter to verify the correct output voltage. in this case it should be 3.3V. In this case the constant-current-driver  outputs 3.3V as well, and the LEDs should run at around 3V, so the resistors must account for that. In this example you would use one (or two) resistor(s) with around 2 Ohms. The PCB is designed in a way that you can use two resistors in parallel, in case you exceed the 1/4w-limit of those resistors, but one should be sufficient also. You can configure the board for up to four individual strains of LEDs, and configure the resistance with resistors (or even diodes for a higher forward-voltage-drop) independently for each strain.

Tip: Cut the remainder of the through-hole-wires on the backside off as short as possible after soldering. the base-cavity is a confined space, and a millimeter more or less indeed matters. the component sticking out of the front the farthest is most likely the JST-XH-Plug. You cannot make it flatter, but you can shorten the pins on the backside as far as possible. The more flush the backside is, the better the friction-fit-cover will fit. Also don't leave any cables too long, they have to be put somewhere also. 

LED Assembly

the filament LEDs are somewhat delicate and fragile to solder, especially the variant with both tabs on the same side, which I used here. Some soldering tips: 

• Use a third hand with soft-grips to clamp the LED in two places to constrain unwanted movement. 
• USE FLUX! 
• Pre-tin the tabs (the conductors are on the side where one of the tabs has a little hole-marking). The tab with the Hole is positive. 
• Solder the pre-crimped JST-XH-connector (ideally shorten the wire beforehand for a good fit).
• I used heatshrink-tubing and some UV-curing epoxy resin to make the soldering-joint resistant to mechanical stress.

Soldering these LEDs takes some practice, but don't get discouraged if it does not work on first try. Be sure to order some spare LEDs, take your time and use FLUX :)

When assembled, I used some thin enamel-copper-wire as guide-cable to gently pull the string through the DNA. Don't pull to hard, the Filament-LEDs cannot handle alot of mechanical abuse. Go slowly and steady. Test the LED-string (ideally with a lab-powersupply at 3V, max ~100mAh per strain). If everything works, cut the remainder of the filament-LED (the LED should stick out of the top by a few cm, this can just be cut off with scissors), then use some hotglue to permanently mount the led into position. 

Optionally the 3D-printed plugs can be placed on top of the Helix to top it off. UV-curing-resin works well here also, but superglue or hotglue will do also I guess.

Final Assembly

When the LEDs are in place, and the PCB has been assembled and tested, you can mount the PCB into place with a self-tapping screw to the printed DNA. Use another JST-XH-Cable to solder the USB-C-Socket to it. I highly suggest, you choose an USB-Socket with some resistors on the data-lines. These tell the powersupply that only power and no data is needed, and some USB-powersupplys only output power when those resistors are present, especially USB-PD-powersupplys. 

Alternatively you can use a PD-trigger-board in the same footprint (you can also use different voltages then, for example if you plan to use a 12V-strip).

Use a lab-powersupply to power the PCB without the LEDs attached. Configure you Powersupply to output more power than you want to use at max (~150mAh times amount-of-channels). Use a multimeter to make sure, you are outputting the right voltages everywhere. Then attach the LEDs and configure the constant-current-driver with a small screwdriver. turn it clockwise just before until the LEDs start flickering. Depending on the lenght and color of the LEDs you will land somewhere in the ballpark of 50-125 mAh per strain. With this setup you unfortunately have some voltage drop across the LEDs, so that they are brighter near the powersource. I haven't found a good way to circumvent this yet, so this is considered to be normal (especially the light-blue LEDs). However, this effect is more prominent on some colors than on others and is mostly dependend on the cable-lenght. Red and Pink are far less sensitive to this. Green is okay also, (light)blue is very sensitive to this effect. 

Cap the bottom off with the included hexagonal plate and enjoy.

Have fun building your own lamp.