Minimesh Solar | Standalone fakeTec Messenger Node

Note: This is a work-in-progress and will likely change over time! Any currently available files are tested and working. Future revisions may fix minor issues, or potentially add new features.

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Presenting my second major CAD project, and a step up from the original in just about every way, Minimesh Solar!

The original Minimesh case was designed to house components that I already had on hand, with minimal printing required at only 2 parts. It was very budget focused and meant to be dead simple to build. Minimesh Solar is a step up from that, with extra (but still affordable) components and a bit more printing. The end result is an overall nicer build, with a larger screen and the ability to charge via sunlight!

Hardware:

This list looks super intimidating at first, but I promise it's not that bad!

• 1x MakerFocus 1100mAh battery (or anything up to 50x30x7mm)
• 1x U.FL/IPEX to SMA pigtail, ideally 5cm
• 1x Assembled fakeTec node based on the nRF52 ProMicro & HT-RA62/RA-01SH (tested with lupusworax's v4 PCB)
  • DO NOT solder the display's headers to the fakeTec PCB!
• 1x 12mm diameter passive buzzer
• 1x M5Stack CardKB
• 1x M3x6x5 heat-set insert
• 1x M3x6 machine screw (pan or button head, not tested with countersunk, though it may work)
• An assorted pack of M2 self-tapping screws, from 4-6mm
  • At minimum, 4 are needed for the fakeTec, 4 for the screen, and 4 for the lid. Lengths may differ depending on your printed parts. May take some experimenting!
• 1x 80mm Solar Panel
• 1x 1.54" I2C (4 pin) CH1116/SSD1309 OLED display
  • If possible, purchase the display with no pin headers attached.
  • If your display comes with pin headers, they must be removed!
• 10x 6x3mm neodymium magnets
• 1x CN3791 MPPT
  • Ensure the listed voltage matches your solar panel! Extra notes on this later down in this description.
  • Most of these listings also include 2 JST-style cables, which is enough to complete this project.
• 1x 2-pin magnetic pogo connector
  • There are several package variations of this part!
  • This project requires the “Male Female” option in the above link
  • Similar parts may be listed as “No Ears” and should have NO screw holes. If in doubt, please send me a message and I will confirm!
• (Optional) 1x Extra fakeTec Button, for the user button under the faceplate
• (Optional) 1x 1/4-20 UNC heat-set insert for tripod mounting
• (Optional) 1.75mm clear filament - insert into the LED holes on the faceplate, and cut flush with the surface for an easy light guide

Also consider having the following on hand:

• Heat shrink tubing
• Tweezers
• Wire strippers
• A set of helping hands

!!! Important Assembly Notes !!!

Because of the DIY nature of this project and the components that make it up, there is a lot of variance in terms of part tolerances. Minimesh Solar was designed with very particular parts, so please read these assembly notes before attempting a build!

I plan to include a step-by-step guide eventually, but for now, the best I can do is some detailed notes. Please send me a message or leave a comment if you have any questions after reading them!

ProMicro Variations:

There are two different form factors that ProMicro boards generally come in, and only one is currently supported. Please ensure that the one you have works with this project!

• If your ProMicro has the USB port level with the top of the PCB surface, then it is not yet supported as the main body will modifications to accomodate a higher port. This will be done eventually, so check back soon, or send me a message!
• If your ProMicro has a “mid-mount” USB port sunken down into the PCB surface, then your board is supported! This includes the official nice!nano (untested) and several clones such as this one.

Soldering:

When assembling your fakeTec for this build, do not use the pin headers anywhere on any components. Solder the Pro Micro flush with the fakeTec PCB - I achieved this by using some clipped diode legs through the holes, and bent in place while soldering. This can be done with a breadboard, too. Some fakeTec PCB variations make surface mounting easier and remove the option for through-hole mounting entirely, which also works.

As for the display, remove the pin headers if yours includes them, otherwise do not solder the pin headers! The display will be attached with short wires instead, as it does not line up with the display pins on the fakeTec PCB. Longer wires will be harder to fit when screwing down the display. I recommend using very short lengths (12-14mm) of thinner wire (26-28 AWG). I also suggest putting some kapton tape (or anything insulating) on the back of the display to avoid shorts, just in case. 

Soldering the pogo pins is really annoying. Soldering irons are made of, well, iron. Magnets are magnetic. The magnets on most of these pogo pins are honestly shockingly strong and will try to pull your iron in at any opportunity. The most effective way I've found is to just put the iron between the pins and feed the solder in from the side facing the magnet. Don't overdo the solder, otherwise it's very easy to bridge the pins, and it's VERY frustrating to remove the bridge! If this does happen to you, just clean your iron, reflow the solder to get some back on your iron, and repeat until the bridge is gone. Use thin wires going to the solar panel (26-28 AWG), and solder them as close to the base of the pins as possible, otherwise it's going to be difficult to make the lid close. I used thicker wire, and it was a nightmare! Work slowly and carefully and you'll be able to solder everything without issue.

The base design supports a user button, however it is no longer needed with the advent of BaseUI on firmware 2.7.0 and above! Both the reset and user buttons on the fakeTec PCB are entirely optional depending on your use case, and you can leave them out without losing any functionality. Ad-hoc pings and GPS can be toggled via CardKB shortcuts or through action menus. 

Assembly and Part Fitment:

This is my first time designing complex and snap-fit parts, and as such, the tolerances can be a little wonky. Please be prepated to do some post-processing, including (but not limited to) sanding, filing, and carefully trimming parts with a sharp blade.

When fitting the solar panel into the lid, it may be difficult to get it to snap into place, and you will likely need to bend the lid and play around with it until you can get it seated. I found that it helped a lot to take a sharp blade and clear out some excess material from underneath the two overhangs (the ones on the top and bottom sides) if it's too difficult to make it fit initially. Just keep fiddling with it and you'll get it in there eventually!

The pogo pins can also be a little tricky to make work. The slot on the faceplate is quite tight, and seems to be easier to fit on PLA-printed parts than other sturdier materials. You may need to very carefully trim the plastic on the inside until it fits, just a bit at a time between each test. It should eventually snap snugly into place. The slot on the lid is a lot more forgiving, as the part is held in place securely when the lid is screwed together, without relying on a snap fit. It may need light trimming, but honestly shouldn't on a well-calibrated printer.

The faceplate itself can be a little tricky to snap in as well. With how it's designed, forcing the corners in will not work, and will likely just damage the faceplate. I like to start at the bottom left side, working one corner in at a time, bending the faceplate to make them slot in a little easier. Depending on your tolerances, you may get a small amount of lifting underneath the screen where the faceplate lacks reinforcement; I plan to address this eventually, and it can be temporarily corrected by trimming down the snaps on the right-hand side of the faceplate (when viewed from the top). Take your time, and be patient! I've built like 4 of these now, and I promise it will eventually go in without issue. 

The user button is a really weird part, and one that I'm considering getting rid of entirely, as it's completely vestigial with the advent of BaseUI and the way it's mounted is extremely bizarre. If you do include it, you're going to want to snap the button into place before anything else. Above the CardKB on the left side, there's a small cavity where the button rests. This cavity is designed specifically for the same surface-mount button that the fakeTec uses. Press-fit the button in place with a pair of tweezers before tinning the pads with solder. Once it's in place, use a fine-tip iron to tin the pads and solder wires to either pin. Solder the other ends of those wires to either the user or reset button on the fakeTec, whichever you like. You'll probably melt the plastic a little bit by doing this, but it ensures a proper fit with the exact right height, and the button should work reliably. No one's going to see the melted plastic under the faceplate anyway!

Notes on Wiring:

As long as you're careful with the lengths of your wires, there's just enough room to get everything connected up nice and tidy. Measure your wires before assembly! This is especially important for the solar panel wires in the lid. If they're too long, it's going to be very difficult to put together, but it's a breeze when they're the right length. 

For the CardKB, keep the wires together, and do not split the ribbon cable apart quite yet. Measure the length of wire you need to go from the CardKB to the SDA/SCL/3.3V/GND pins on the bottom of the fakeTec. To make things easy, after you cut the wires to the right length, solder these wires to the same pins the OLED display uses.  ** Yellow to SDA, white to SCL/SCK, red to 3.3V, black to GND. **

Ensure the buzzer wires are fairly short and do not go much further than necessary for the buzzer to fit the faceplate. Do leave a bit of slack to ensure you can attach it to the faceplate when everything is installed inside the main body. It can help to also bend the pins 90 degrees to ensure the faceplate sits flush, without the buzzer pins touching the main body.

Notes on Configuration:

When you first power on the unit, the screen is going to be a glitchy mess. It's not broken, and you didn't wire it wrong! Connect your unit through the mobile app, and head to the radio configuration screen. Under “Display,” you're going to want to change the “Override OLED auto-detect” setting from OLED_AUTO to OLED_SH1107, and apply changes. It should then reset, and the display will look correct!

For the CardKB to work, if you're running firmware 2.7.0 or higher, the CardKB should be picked up automatically without any extra configuration, and you may just need to perform a single reset. If you're running a firmware earlier than 2.7.0, make sure the canned message module is enabled. You may need to reset the node once or twice for it to pick it up. You don't need to specify any specific input device, as the firmware will automatically detect it!

Happy messaging!

Please feel free to shoot me a message if you have any questions! You can find some of my contact information on https://5panel.dance or message me/leave a comment here on Printables. I respond quickest over Discord, but I will get back to you via email as soon as possible too!

Print Suggestions:

• Print me in ABS, PETG, or ASA! I might melt or warp in direct sunlight if printed in PLA. Ask me how I know.
• No supports needed for any parts
• Print the faceplate face down
• 25-30% infill on the main body, with extra walls (5-6) for strength
• 50% infill on the faceplate (optional, worked well for me)