Projects

Go Big Or Go Home!

48:1 Scale Giant LED Lamp

Daniel Koch & Johann Wyss

Issue 27, October 2019

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Whether you’re an enthusiast, weekend maker, engineer, or full-time nerd, we think you’ll love this giant LED decorative lamp as much as we do!

BUILD TIME:1 Hour PER BUILD (excluding printing and Painting time)
DIFFICULTY RATING: BEGINNER

At DIYODE, we like to do things ‘just because’. When it’s a supersized ‘just because’, even better!

There are few components which embody modern electronics as much as the humble LED. Even though they’ve been around for decades, they persist in our projects and much more, every single day. In fact you may even struggle to find a traditional globe soon.

Always the most exciting feature of learners’ kits, with their colourful, translucent plastic cases and rich coloured light, LEDs themselves have taken drastically different new forms in the last few years, with developments from the older Luxeon LEDs to Chip-on-Board (COB) lights. Despite this, the humble 5mm, T1 ¾ package remains the icon with its little sibling, the T1 3mm package.

This T1 package is the iconic style and what most of us think of when we think of an LED. So what better basis for a supersized project?

When our staff writer, Andy Clark, first showed us his supersized LED, we instantly wanted to bring it to DIYODE readers as a project. Andy’s original work was designed for his own ends, rather than as a published project, so if you come across Andy's original idea, you might notice some differences between the original idea and this developed project.

Our development process has resulted in two versions of this lamp.

The first features a glass dome and white light. It is as true-to-form as we can achieve, with a 3D printed anvil and post holding a COB LED (perhaps ironically) as the light source.

The second is fully 3D printed including the dome, in translucent material that diffuses the light and hides the internal form. This version is presented as an RGB lamp using USB-powered strip on a helical former, but you could also use high-brightness white LED strip or just about any other light source, since the internal components can’t be seen on this version.

RESEARCH AND DEVELOPMENT

Our first challenge was to locate a suitable dome-shaped capsule to use. While Andy sourced his from IKEA, it was in the clearance bins and no longer a stocked item. After searching high and low for a verifiable, consistent supply that could be accessed by anyone from Sydney to Laverton, we gave up on acrylic domes. While we wanted plastic for safety and durability, the few we found had handles or knobs on top.

The same can be said for glass, except that we did find a couple that were a clean, smooth dome. Commonly called bell jars or cloche jars, most of these had a knob or handle too, but some do not, and it’s these that we are after. We settled on one from IKEA, as supply appears to be reliable and IKEA sell in-store and online. This makes them accessible to anyone in Australia, no matter how remote, and to those outside Australia too.

The second challenge was choosing a light source. Because the insides of the lamp were to be 3D printed, we need a light source that runs relatively cool. Many high-brightness LED types, such as the star type, Cree’s round high-intensity modules, and many COB lights, run at quite high temperatures. Often, the metal housing of a torch or lamp is used as a heat sink. Not possible in our case, and even an internal heatsink is not desirable. 3D printed plastics don’t respond well to this.

After looking at many suppliers, we found some options that would work, but with accessibility in mind, we rejected them. Most were business-to-business suppliers, and none was really easy for the general public to buy from. After a head-smashing brainstorming session, it was decided to use the light source from a plastic keyring light or torch, that was reasonably small, entirely plastic, and battery powered. These criteria would guarantee a light source that did not generate much heat and didn’t draw much power.

The solution we settled on was the ST3432 COB torch from Jaycar. Running on three AAA batteries, the rounded COB light was entirely housed in plastic. So, one was obtained and duly opened. An inspection revealed an SMD resistor on the underside of the board, with a value of 1.2Ω. Great! So all that was needed was to connect 4.5V, and we’d have light!

We did, lots of it, and not for long. The lab power supply showed a current draw of 780mA, far too high for this kind of light. Sure enough, within four minutes, the lightsource had dulled, yellowed, and finally, expired. A second torch was opened up, and this time, current was measured within the torch circuit, with the aid of some small wires soldered at strategic points. This showed that the COB light draws 280mA at 4.5V. Dismantling the original torch revealed no resistor anywhere, not even hidden in the switch. Measurements on the still-functioning torch showed that the resistance of the stamped-metal contacts and wiring, combined with the internal resistance of the AAA batteries, was enough to limit the current.

Now all that remained was to verify our figures. The COB light was removed from the torch, and soldered to a 10W, 10Ω resistor that happened to be on the workbench. Running this at 5.8V gave us the desired display of 0.28A on the power supply. We left this powered up for a grand total of five days, twenty-four hours a day, with no visible loss in performance of the COB light. Non-contact thermometer readings also revealed that the COB light was running at 49°C, and the 10Ω resistor at 43°C.

We had chosen to run the lamp on 5V, we ended up with a 6.8Ω resistor. This gave slightly less than full brightness, but ensures relatively little heat generation and longer COB life.

LED STANDARDS, OR LACK THEREOF

Once upon a time, long, long ago, there was a standard for LEDs constructed in the T1 or T1 ¾ packages (and others). Generally, the anvil was the cathode, or negative side, and attached to the short leg. The post was the anode, or positive side, and attached to the longer leg. The cathode was also indicated by a flat spot on the rim. This made life easy for anyone using them.

Unfortunately, this standard became irrelevant some time ago. Why? Because of China. Manufacturers there are famously effective at making things to not quite world standards. We have even come across it on the workbench, with an electrical appliance that we suspected may be a bit dodgy. Although the Chinese manufacturer had used Australian-standard wire colours for the active, neutral, and earth connections in the flex cord, they were not connected in the correct order, and the earth wire was carrying the active.

LEDs are no different. Virtually all come from China now, and even those from established and reputable manufacturers don’t always conform to the old standard. The DIYODE workbench contains batches of LEDs with anvils connected as the cathode, almost as many with the anvil as the anode, and some that are rimless versions of the same. The only consistency is the short leg being the cathode and the long leg being the anode. Even then, we have one batch with legs the same length! All of this made design decisions for our lamp just that little bit murkier.

DESIGNING A LAMP

We decided to construct our lamp to scale, using a regular 3 or 5mm LED as a prototype. This meant taking measurements from an LED off the workbench, and scaling them to suit our glass dome. While the rim at the base of many (but not all) LEDs looks fairly thin, in fact, it became surprisingly large when scaled accurately. This turned out to be useful, as the IKEA dome is quite tall. Rounding off at 29mm, the scaled-up base has a 24mm recess for the glass, and 5mm for a strong floor. The 5mm LED measures at 4.9mm diameter and 5.62mm between the top of the rim and the beginning of the curve at the top. Scaled to the 142mm wide glass dome, this gives a scale factor of 1:28.97 to two decimal places, so we called it 1:29 and moved on.

The IKEA dome is 188mm between the bottom edge and the beginning of the curve. At scale, this length needs to be 163mm. Recessing the glass 24mm into the base means that we have a height of 187mm, pretty well spot on. The rim measures 0.4mm wide, giving us 11.2mm either side of the dome. Combined with the glass dome’s diameter, we went for an overall print of 166mm.

There was much discussion about the form of the anvil and post inside the LED. The design you see is the result of examining several clear LEDs, and cutting the resin package off one to take measurements from the actual anvil and post. Modifications were made to suit the COB and conceal the wires. Andy’s original version had two visible wires, but we wanted to, as much as possible, only show the small wire that crosses the gap between anvil and post. This meant some craftiness with Fusion 360 to gain a wire path, but eventually, we used a drill, as slicing programs wanted to add supports into that part of the print.

The final design as presented features a base that accepts the anvil and post on top, legs from underneath, and mounts the glass. This keeps the print for the post and anvil from being too tall, as it would be if the legs were attached as one long print. The base will be too wide for some printers, so we have also included a version divided into thirds which can be glued together. The whole assembly is mounted on a faux breadboard. We chose to model one side as the edge of the board, which is slightly wider with no contacts, as a way to fit the switch and power sockets.

Additionally, we explored colour options for the anvil, post, and legs. Original prototyping was done in an aluminium-finished grey PLA. We have not always had the greatest success with this product, and truly metal-look filaments are expensive and fickle. So while you may choose to model these in a metal-look filament, we went with tried-and-tested white PLA, and painted it instead. We will detail that soon.

3D PRINTING

Some of the 3D prints we have supplied .stl files for, need to be handled in a certain way. If your printer has a small build volume, you may need to cut the height of the legs, anvil, and post.

Depending on which build you're making, there are a few differences in the prints. However some parts are common.

For this reason, we're describing the printing for both together.

a. Breadboard (TWO VERSIONS)

The faux breadboard is the base that supports the lamp, and houses power connections. It should print upside down to avoid supports, but we have presented two versions. One has a power switch and socket, and is used for the glass domed, white light version. The other has just a hole for the USB cord to pass through, and is used for the RGB, 3D-printed dome version.

B. Base (COMMON)

This item should print as is, but needs supports for the recess. Some slicing programs will try to fill the recess for the dome with supports if you try to print upside down, and these will be irremovable. We printed with four shells for strength where the legs and anvil/post join, and 15% hexagonal infill. The same base is used for both glass dome and 3D-printed dome versions.

C. Legs (COMMON)

These are designed as a plate with the legs attached. This added strength over our original design, but necessitated a recess in the base. We printed this item upside down.

D. Anvil and Post (GLASS VERSION ONLY)

Print the anvil upside down with its top on the print bed to preserve the cable holes, but does mean the recess for the COB light will need supports for a flatter, even surface for the COB light. The post can be printed upside down or flat to avoid it falling due to the small contact area.

E. Dome (RGB VERSION ONLY)

This can be a little challenging. The solution when we printed it was to use maximum shell count (10 for us, more than needed but the printer figures the rest out) and 100% infill. Using any percentage of infill below 100% will show the pattern when it is lit up. We have provided a version cut in half, with a locating rim, for smaller printers.

F. Helical LED Core (RGB VERSION ONLY)

This houses the LED strip for the RGB version. Designed to taper, it is best printed upside down with supports to hold the overhangs on the LED strip guide. If the model is printed the right way up, space the base above the build plate and add supports to hold the base.

FINISHING OPTIONS

While you can print in metal-finished filament for the legs, anvil, and post, we found that printing in white PLA was more successful. Our printer likes this filament and it has no quirks. But that's not how an LED looks!

To make this look like metal, we chose an automotive paint called ‘Dupli-Color’, which can be sourced from automotive parts chains virtually anywhere.

This is a very strong lacquer paint made here in Australia under licence from its USA-based owner. The array of finishes available is impressive, and we found one labelled as ‘nickel’. This was likely to be the closest to tin-plated component leads.

Painting 3D printed parts has a procedure of its own, so we’ll summarise it here. It applies to both versions of the LED, although only the legs are required for the RGB version.

Lightly sand all surfaces (those to be painted) of the parts with fine sandpaper, at least 1200 grit. This step may not be necessary if your primer is definitely meant for plastics only, such as model-makers’ primer or some automotive plastic primers.

Spray them evenly with a coat of primer. Regular aerosol safety rules apply: Ventilate, and use a mask, preferably one with a charcoal layer. The primer we used is clear, as are many that are meant for plastics. If you are not using a dedicated plastic primer, it will probably be grey or white, and sanding is essential.

When the primer is dry, coat with your chosen finish. We used a shiny chrome silver automotive paint, but if you can access modellers’ paints, your colour options will be greater. Some model paint ranges even include different paints for new versus old aluminium. More than one coat will be needed, so follow the manufacturer's instructions regarding recoat time.

The finished product will have a great metallic sheen!

Build 1:

Glass LED Lamp

Parts Required: JaycarAltronicsCore Electronics
1 × Keyring Torch with COB LEDST3432--
1 × Glass Dome (or similar)-IKEA: 203.273.04-
1 × 2.1mm Bulkhead-mounted DC SocketPS0522P0622ADA610
1 × Rocker SwitchSK0984S3201POLOLU-1406
1 × 6.8Ω 5W ResistorRR3246R0321-
1m × Twin-core Speaker Wire or 2 × Individual Hook-up WireWB1702W2105-
50mm × 1.5mm Heatshrink WH5530W0910AADA334
20mm × 5mm Heatshrink (for Rocker Switch Contacts)WH5533W0913AADA334

Parts Required:

Adhesives, paint and painting accessories also required.

This build is really focused on replicating the true look of a watercolour clear LED.

Naturally, there are a few trade-offs and embellishments in order to make it appear realistic, while handling limitations such as the availability of hardware.

One of the key features of this is the use of a COB (Chip On Board) LED as the light source, which we hack out of a battery powered COB light we found at Jaycar. You shouldn't have trouble finding one of these at your preferred vendor.

Based on the high volume of these LED torches being sold, they're very cheap at a retail price. While we could find similar LED-only options around, their cost was more expensive than just buying the torch and extracting the LED from it.

The core anvil and post design has been revised a few times to get the look we wanted, and you'll want to pay special attention to the print finish as discussed in the 3D printing section, since it's all on display and important for the overall visual success of this build.

The electronic side of this is very straightforward, and the schematic/Fritzing is really only provided for double checking, as you could probably figure it out anyway.

Outside of the 3D print time, this build could be completed quickly and we're confident you'll love the finished look.

The only tough part to source is the glass dome. We have provided the IKEA part number for the one we found which works precisely with our supplied printer files. You may need to tweak the design if you source a different dome. If you can't find the glass dome (or want a frosted dome), we suggest tackling the fully 3D printed version instead.

The BUILD

Prepare by printing the base, anvil, post, and legs. and prepare them as per the guide in the 3D printing section of this project.

Start by carefully dismantling the torch to remove the COB light source. Cutting the side of the head works well. Snap off or desolder the contacts.

Solder a wire for the positive connection to the centre of the underside of the COB light. Solder the negative wire to the pad on the top surface, marked ‘-’. Be careful, as ‘+’ is right next to it.

Assemble the base and legs as shown with your chosen glue. Gelled cyanoacrylate glues work best here and if you have a setting agent such as ‘Zip Kicker®’, use that too. Be careful that the holes in the legs align with the holes in the base so the cables can pass through.

Drill a hole in the anvil in the centre to pass the positive cable. Drilling on an angle will send it into the cable channel down the leg.

Feed the wire for the positive connection on the COB light into the cable hole in the anvil. You may need to coax it to make the turn inside the leg. Pull some out of the bottom of the leg. With the COB seated, glue it in place with a small amount of hot melt glue, or another adhesive of choice.

Feed the negative wire down the post, leaving some slack in the wire to replicate what can be seen through the side of a clear LED. Glue this in place inside the post so the glue is not visible.

Guide both wires from the anvil and post through the legs until the anvil and post can seat into the base. They should not need glue.

Feed both wires from the bottom of the legs, through the holes in the breadboard where the LED will mount. Slide the legs into the breadboard.

Solder the positive wire via the switch to the power socket. Connect the negative wire to the 6.8Ω resistor, which itself connects to the power socket’s negative terminal.

Plug in a 5V plug pack and turn the switch. Your LED should light up! If it does, you can choose to glue the legs into the base, or leave them as a friction fit.

Gently ease the glass dome into the recess until it is seated all the way in. Marking a line with marker 25mm up from the bottom will help you measure progress. Clean this off, along with any fingerprints, afterward.

Build 2:

RGB LED Lamp

Parts Required:JaycarAltronicsCore Electronics
1 × USB RGB LED Light StripZD0571--
1m × Ribbon Cable (four cores)WM4516W2510CAB-10647
50mm Breadboard Wire Link (or similar wire)WH3032P1014ACE05631

Parts Required:

Adhesives, paint and painting accessories also required.

Not all LEDs are clear, many have a coloured case. This build is totally 3D printed so there's no need to source the glass dome, and it boasts RGB colour versatility using off-the-shelf RGB strip. It still retains a true-form LED style and looks amazing!

During the development process, we had considered a Neopixel LED as a cool-running LED. While we rejected this because of the need for a controller, it did prompt interest in the idea of an RGB version of the LED lamp. After much discussion, the current design resulted. Because the translucent material hides the internal form, there was no longer a need for a small, round light source of the correct size.

Our in-house CAD magician, Johann, cleverly created a way to use the existing leg and base structures. A copy of the glass dome was modelled so that it could be printed in a chosen filament. Inside this, mounts a helical structure with a base designed to align with the receptacles for the anvil and post. The whole model mounts on the same faux breadboard base as does the clear / white version.

The helical channel houses RGB LED strip, for which we went with a one metre long, USB-powered strip that has a small controller built into the base. We needed to move the controller away from the end of the strip so that it was accessible outside the lamp. It connects under a piece of heatshrink with header pins, and the sockets are the same size as IC sockets. This ruled out using regular PCB header pins, so we went with lengths of breadboard wire links instead. You’ll see this in the instructions. We connected a length of rainbow ribbon cable to avoid mixing connections, but if you want to, you can use grey instead.

The use of the helical former and LED strip means that you could use high-brightness 12V LED strip instead. You could modify the former into a vertical, rather than tapered, spiral, and take the LED strip all the way to the top. This would make a very bright light indeed! The same is true of the five metre RGB LED strips around. These would require the concealment (or display) of an external controller.

The BUILD

Prepare by printing the base, legs, breadboard, and helical core. If you wish to paint the legs, do so prior to assembly.

Glue the legs and plate to the base. Rest the helical core into the holes in the base, and sit the assembly in the breadboard.

Cut the heatshrink off the join between the controller and the LED strip. Separate the two items, saving the header pins that join them.

Peel four cores off a length of ribbon cable. The length is determined by where you want the controller to be. We used one metre. Strip and solder the wires at one end to the header pins that joined the LED strip and controller. Heatshrink your joins.

Curl the ribbon cable and feed it through the hole at the top of the LED helix as shown. Make sure it follows through and comes out at the bottom of the leg. It may need some convincing to pass the join between helix and leg inside the base, and the leg and breadboard junction. None of these joins should be glued yet.

Feed the ribbon cable out through the hole in the side of the breadboard. Cut breadboard wire links or similar gauge solid-core wire about 12mm long. Strip and solder the remaining ends of the ribbon cable to these pieces of wire, and heatshrink the joins.

Insert the header pin strip into the LED strip where it originally went. Insert the wires at the other end of the ribbon cable, one by one, into the socket on the controller, paying attention to wire order.

If the joins between breadboard, legs, base, and helix are not firm enough as interference fits, glue them now. We have found gelled superglue works best. Peel some of the tape from the LED strip, and begin attaching it to the helix from the top down. Pull more backing tape off as you go.

You may have some LEDs left at the bottom. Trim this if you do, at one of the marked lines on the product. With the LED strip in place, gently pull back any slack in the ribbon cable from outside the breadboard, so that there is minimal curled spare cable inside the dome.

Connect the USB plug to a USB power source and make sure the strip lights up. If it does, you can install the dome. You may also like to add some heat shrink to the end of the controller to hold the wires in place, but be careful not to obstruct the buttons.

There are three buttons to play with on the controller. The ‘mode/demo’ button selects between flashing and fading modes, or ‘demo’, which is a sequence of all of them. The ‘speed/power/brightness’ button, when held, will turn off the lights. When pressed, it will decrement the speed of the effect. There are nine steps. In single colour mode, it will vary the brightness in eight steps. The ‘color’ button interrupts any flashing or fading mode and selects a single colour with each press. This colour will stay lit, you will have to press the ‘mode’ button again to return to a flash or fade.

WHERE TO FROM HERE?

If you want an even finer finish on the painted parts, you could try a spray primer such as the type used by car enthusiasts for minor repairs and modifications. Unlike commercial products, these are sold in aerosol cans and are a single-part spray putty. They are somewhat self-levelling and will fill any lines between print layers. They are sanded before priming.

You could, if you have experience or are feeling adventurous, try exotic filaments like PETG (which gets mixed results from varied people) or ultra-clear filaments. We have experimented in the past with these and found them harder to work with. We haven’t succeeded but people who have achieved very impressive results.

You could also modify the glass-domed version if you can find an RGB COB light. This may need extra wires and a controller, or maybe the two-wire internally-controlled sequencing type. We also thought of printing a larger, non-tapering former for the 3D-printed dome version, and filling it with as much RGB or plain white strip as possible.

Daniel Koch & Johann Wyss

Daniel Koch & Johann Wyss