Hanging Solar Node - for use with Meshtastic and Meshcore LoRa Devices

Overview:
This enclosure is designed for outdoor solar nodes/repeaters to be hung from tall objects such as trees, giving users the ability to place their nodes at higher altitudes on their property when they don't have the ability or desire to climb roofs or towers.

The body has slots for 3 solar panels. The base has a hole for N-type antenna. The two pieces are attached with three M3 heat-set inserts and socket head cap screws. There is a slot in both pieces to accept a gasket, meant to prevent water ingress. The solar panels are meant to be seated and sealed with silicone caulk.

There are two different body versions - the default has a shallower angle which is an attempt to match the solar panel angle to my latitude, but this makes the footprint much larger. There is a second body design which is much more compact due to a steeper solar panel angle.

This is an ongoing experimental project. Points of ongoing consideration/study include:

• Are these three solar panels adequate to keep the battery topped off? Initial tests with just the electronics outside of the enclosure suggest that on moderately-cloudy to sunny days, the battery had no issue staying up above 90% with these three panels in parallel. Will continue to monitor this in the context of the enclosure. Brought inside with no exposure to sunlight, the electronics stayed alive for over a week and only went down to 40% battery.

• Is the silicone caulk and gasket adequate to prevent moisture issues? Future points of consideration include potentially adding a hole to the base to accept a breather valve. May install SHT40 or similar moisture sensor on the board to monitor internal environment at some point. Currently running meshcore, which separates repeaters and sensors, which makes this slightly more annoying to do.

• Is the current tie-off feature strong enough in the face of high winds? Layer orientation is a concern, but an attempt to mitigate this with many perimeters has been made.

Bill of Materials with Sources:

• Gasket: OD: 3.05in, ID: 2.36in, Thickness: 0.21in https://www.amazon.com/dp/B09JBDYBJR?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

• Antenna: N-Type Male connector https://www.amazon.com/dp/B0F7HCPPHF?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

• Pigtail: IPEX to N-Type Female https://www.amazon.com/dp/B0DPMD3226?ref=ppx_yo2ov_dt_b_fed_asin_title

• Board: Heltec T114 (any board compatible with Meshtastic or Meshcore will work. nRF52840 boards are recommended for solar nodes due to their small power usage compared to ESP32 boards)

• Solar Panels: 5V, 200mA, 1W solar panels x3. 110mm x 60mm x 2.5mm: https://www.amazon.com/dp/B0BML3PR4Z?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

• Battery: Adafruit 3.7V 1200mAh LiPo.  This is just what I had laying around. So far, it seems to be a high enough capacity to keep the board alive with its periodic exposure to sun. https://www.adafruit.com/product/258?srsltid=AfmBOopkG46-SDMR8xneubINzTMXrAlEiLt-eyCmX9NkIM8MsbOdU2rA

• M3 Heat-Set Inserts: 5.5mm OD, 5mm height https://www.amazon.com/dp/B0DSKRS5MN?ref=ppx_yo2ov_dt_b_fed_asin_title

• M3 Socket Head Cap Screws: length of 12mm, you can find these anywhere. Consider splurging on stainless or other corrosion-resistant options

• Silicone Caulk: can be found at any home improvement store.

• Three Diodes: these will prevent cross-flow between the three solar panels while one is in light and others are in shadow. Look for diodes with a low voltage drop (aka forward voltage) and that won't limit the current draw from the panels too much.  https://www.digikey.com/en/products/detail/sanken-electric-usa-inc/RA-13V/4454783

• Optional - JST connectors: Depending on your board, battery, solar panels, etc., you'll probably need some connectors. I used some that I had laying around from other projects. Be aware of the JST2.0 vs. JST1.25 size difference between the LoRa board, solar panel, and charger board.

• Optional - Solar LiPo Charger Board: The T114 board used for this project has on-board solar power management, so one of these boards were not needed. If your chosen board does not support solar charging, you will have to pick up a board like this that manages battery charging and device power: https://www.amazon.com/dp/B082F7X8WS?ref=ppx_yo2ov_dt_b_fed_asin_title

Printing Suggestions:

Initial prototypes were made with PLA and sealed with primer, indoor/outdoor spraypaint, and a clear matte sealer, since I don't have access to an area where I'm comfortable printing more weather-proof filaments due to fumes and enclosure requirements. PETG or ASA would be a superior choice if you have access to that.

Depending on your slicer, you may encounter some scaling/units issues when you bring the STL in. If the parts come in looking very tiny, scale them up by 2540%. The overall height of the body should be 4.129in, and the overall height of the base should be 0.7in. As long as you scale all dimensions evenly, this should ensure a properly sized part.

Layer Height: 0.2mm - some of the bridging layers were designed with this layer height in mind. If you choose a layer height substantially larger than this, you may have issues with the 'roof' of the body.

Supports: No supports needed. The bridging at the top of the body is a little aggressive, and you might have some drooping, but it certainly shouldn't fail. Keep the top layer count high to build up enough thickness, even in the case of drooping bridges.

Perimeters: 4, Top and Bottom Layers: 4 or 5. These were kept high to help with water-tightness. If you're using a better outdoor filament other than PLA, you can probably decrease this for most of the body. If your slicer allows variable layer height, I'd still recommend keeping perimeters at 4-5 in the top hanging feature on the body to aid with strength.

Infill: 15%

The photo example was printed with fuzzy skin on the outside with the default PrusaSlicer settings. I like it aesthetically, and I think it does add to the total amount of extruded material and therefore wall thickness (and hopefully therefore water tightness?). This isn't required, though.

Assembly Instructions:

1. Print the body piece and the base piece. Seal the prints for weather protection as you see fit based on your filament selection.

2. Install the heat-set threaded inserts.

3. Solder a diode in the forward direction in series with the positive wire coming out of the solar panel. Repeat this for the other two panels. These will prevent current flow from one panel to another in the case where they are unevenly lit.

4. Connect the three solar panels in parallel. How you choose to do this is up to you, but remember that they have to be routed through three separate holes in the enclosure. The wide slots in each of the panel pockets are large enough that the panels can be fed sideways through the slot, into the main cavity of the body, and out through another slot. This means that you can solder all of them in parallel first, and then carefully feed them into the enclosure one-by-one. This requires that you be gentle and patient.

   1. Alternatively, you can seat them in the enclosure separately, and then solder them together through the bottom hole, but you will need your wires long enough that they can snake through the bottom hole of the enclosure for access while soldering.

   2. There are other alternatives that involve additional connectors. It doesn't really matter what your wiring/harness strategy is as long as the panels are wired in parallel and eventually lead to a single JST connector that goes to the solar charging board or LoRa board.

5. To seat the solar panels in the enclosure, run a small bead of silicone caulk along the inside edge of the rectangular panel pocket. Gently squish the panel into this bead so that it seats in the pocket with a nice seal under it. Run a slightly more generous bead (seriously, don't overdo it) along the perimeter of the top of the panel, filling in the gap between the panel and wall. While the caulk is still wet, use a rounded credit card, piece of cardstock, or gloved finger to swipe along the bead and smooth it to a consistent, concave profile. Keep your tools clean and apply the bead with discipline - this silicone sticks to everything and can create quite a mess if it starts smudging and stringing everywhere. It can be cleaned with mineral spirits prior to curing.

   1. Repeat this for the two other solar panels. Allow the silicone to cure for 24 hours before proceeding.

6. Put the N-type female adaptor through the hole of the base. Use the included nuts/washers to secure the adaptor. Before attaching the IPEX end to the board, string the gasket over the pigtail. Attach the IPEX end of the pigtail to the LoRa board. Attach the antenna to adaptor on the outside of the base.

7. Connect the solar and battery connectors to the LoRa board (and charging board if using this). Be sure to do this after attaching the antenna, as powering on the LoRa board without connection to an antenna risks damaging the board.

8. Gently feed the wires, battery, and board(s) into the main cavity of the enclosure. Pay special attention to how the IPEX is being treated. If this is under too much stress, it risks popping off, disconnection the antenna from the board, and potentially frying it.

9. Mate the base with the body, aligning the screw holes and making sure the gasket is sitting evenly in the trough. Thread in the M3 socket-head cap screws, tightening in a star pattern to ensure even pressure on the gasket.

10. Hang your node - I suggest using the "PCT Method" typically used for hanging bear bags while camping in the backcountry. Details on that can be found here: https://theultimatehang.com/2013/03/19/hanging-a-bear-bag-the-pct-method/