Display Cup MK2

A few years back I created the original Display Cup and posted it here (https://www.instructables.com/Display-Cup/). Despite it not being all that practical, it did serve as a good proof of concept. It also represented that rarest of things among overly creative people like myself: a finished project!

While I had lots of ideas of where to take it next, I didn't do much except think about it for some years. I did try to make a better cup using acrylic sheet and bending it to shape, but this didnt really work very well. It was not until another instructables user inquired about the cup. He proceeded to make one himself, which was awesome and very encouraging. We have subsequently become friends as a result!

This got me fired up about revisiting this project to make a much better design. To that end, I bought something I'd wanted for a very long time, a 3d printer. Shout out to Cherry Blossom Development for funding this purchase!

In this new design I had a few specific goals:

1. A bigger display. The original had a 2.13" display. The new design will have a 2.9" screen, which is the biggest practical display I could find.

2. A more usable cup instead of the cheap plastic novelty cup.

3. A proper insulated design.

Comparison to existing products..

I wanted to add that in comparison to existing fancy coffee cups:

1. Display cup has a removable, machine washable insert
2. The insert is borosilicate non reactive glass so no unwanted tastes are added to your drink
3. Its insulated but not continuously heated, which is good to preserve the taste of coffee in particular. You don't want to keep cooking your coffee which imparts a bitterness to the flavor.
4. You can also eschew the glass insert and put a can of your favorite cold drink and it will keep it cold.
5. You can keep other cold drinks cold in the glass insert.
6. You can forgo the fancy electronics and just use a printed paper insert, eg a photo or a kids drawing.

1. Insulated cup with glass insert.
2. E-ink display
3. FFC ribbon cable (select 10cm and 24 pin)
4. low profile cable extender
5. Esp32 microcontroller with e-ink driver
6. Lipo charging board
7. Lipo battery
8. 3d printed cup components
9. Some wire, solder, and solder paste
10. Kapton tape or other suitable tape
11. Sticker paper sheets

Adventures in 3d printing begin! I opted for a resin printer for it's detail accuracy and the ability to print transparent resins. The Elegoo Saturn 3 12k printer was a good compromise between price and quality and has worked well for this, especially as I am a beginner at 3d printing. My first prints were successful, but I did have a few failed after that. I guess I got lucky at first.

For the cup itself, I used anycubic high clear resin, and for the base, their ABS like pro 2 resin.

To get it really clear you can carefully try to cure it right off the printer while it's still wet. That's tricky to do. I also tried spraying it with gloss acrylic clear spray paint. But even just washed with IPA it's still clear enough to see the e-ink display.

The final design I arrived at uses two parts for the base, an inner cup wall and an outer clear cup wall. To accommodate the ribbon extender, which is 2mm thick, I've designed the inner and outer cup walls to have enough space (including a hole on the inner cup).

I also had some issues with shrinkage in the prints, largely because it's a tall print with lots of empty space. I think having the area heated might have also contributed. Keeping the resin warm though helps with the details of the prints.

I designed in a bulge in the outer clear cup, which is barely noticeable when printed, but it seems to have solved the issue.

In order to keep the gap between the insulated cup and the outer 3D printed shell and minimal as possible, I initially tried to carefully solder the ribbon to the display. I had one success in doing this and several fails, as the displays are extremely sensitive! I then was informed of a low profile connector that I could use instead of the bulky ones you get with the screens. Thanks to the folks on The Hardware Academy!

Soldering method:

To do this, you'll want to "tin" the contacts on the display module FPC (Flexible Printed Circuit).

The FPC is made of a high temperature plastic so it won't melt easily, so we're going to put some solder paste on the e-ink display contacts. Then, melt some solder onto the tip of your soldering iron, and quickly touch the contacts. The solder should flow easily onto the contacts, coating them with solder. Make sure not to bridge any contacts. You may need to move the iron back and forth over the FPC a few times, or even use the pointed tip to separate any bridges.

The displays are extremely delicate and I've already ruined a few, so I recommend taping it down (but use tape thats not too sticky so you can get it off easily).

Use some alcohol to clean the FPC of the solder paste residue, let it dry, and then put a thin layer of solder paste on top of the now tinned connections.

Next, you'll want to use a small bit of wood or plastic on one side of the FPC, and use this to position the FFC (Flat Flexible Cable) directly on top. Leave some of the display FPC where you have solder exposed. Have a plastic "pusher" so you can push down on the FFC (a spudger stick is perfect here) while you solder it. Using your iron, touch the exposed solder right in front of the FFC and melt the solder. You should see it get sucked under the FFC as you press down. Move the iron across the contacts, making sure to press down on each. Do NOT touch the FFC as it will melt! Also be sure not to create any solder bridges.

This is the hardest part of the whole project. You will want to connect the FFC - FPC display to the micro controller and be sure that it works before final assembly.

A better, proper way to do this would be with a mask to apply solder paste, and then gently heat it with a reflow device. I don't have these, so I couldn't do it.

Connector method:

Use the low profile connector. Done! However this means needing an additional at least 2mm gap in the cup (which is how my 3d models are now designed).

Now that you have a display attached to the ribbon, we can attach the display to the inner cup wall. There is a notch where the connector will fit in, if you've done the easy method! Place the connector in there, and then carefully arrange the display to fit into the embossed area. Use some tape (I recommend some kapton tape, but clear wrapping tape will work as well to hold down the ribbon side, then carefully wrap the display and put some tape on the other end.

The ribbon cable will need to be folded at a 90 and passed through to the bottom. I added an opening in the inner cup near the bottom for this purpose, but it turned out it was not needed as you can easily pass the ribbon on the back side.

Now, you will use the printed sheet to cover the edges of the display and match the color, which is not quite white. Use a blade to cut the rectangle for the display. For this, you will definitely want to use some clear packing tape, or use something like rubber cement to hold down the paper. Or for the best results use a sheet of sticker paper to print onto. I checked for fit before peeling off the backing.

I used a simple, small LiPo charging board from Aliexpress and the Waveshare ESP32 e-ink driver board. The battery is a small one I salvaged from a vape device. Any kind of a small LiPo works here, around 250 - 500mah.

The charger board is marked with a B- and the matching hole is just above it, this is where you will attach the black and red leads from the battery. The outermost holes labeled OUT- and + are where you will attach wires for the micro. I used wires with female ends so they can connect to the micro without soldering, but this requires bending the pins sideways.

Of course, you will want to program the micro before the final assembly. The github is here: https://github.com/greywire/displaycup-2. It's the simplest example that works so it should be easy to follow the code. Right now it's just loading a rotation of simple phrases.

The outer cup should fit snugly over the inner cup and display assembly. At this point you can decide which side of the cup the handle will be on, if you are left or right handed and if you want the display visible to others or yourself.

Once the outer cup is slid all the way up to the top, insert the innermost insulated metal cup. It should snap into the inner cup at the top, and then you can attach the spacer ring / support. To secure this in place I simply spot glued it to the inner cup. I used Bondic which is a thick resin that is cured with a little UV led. In this way if I have to I can chip those off to disassemble.

Then attach the ribbon to the micro. It should face up, just like on the connector. Finally, match up the screw holes on the base. I used small eyeglass screws here, although I probably should have chosen something a little bigger as they were difficult to line up.

Take you cup anywhere and let people see it. :)

If you would like to purchase the 3d printed parts and/or a complete kit please let me know. I would like to get the cups injection molded, but in small quantities I can print them out myself.

Purchase the 3d prints: https://nerdprovisions.com/product/display-cup-mk2-3d-prints/