Meshtastic Solar Buoy

This Instructable shows how to repurpose an inexpensive solar anchor buoy light to build an extremely durable and waterproof solar powered Meshtastic node. I've included #affiliatelinks to the supplies and tools that I have personally used, so you can help me buy stuff for future how-to Meshtastic projects 😎

The 6V solar panels, 18650 battery, and waterproof case work great when paired with a RAK 19003 WisBlock Meshtastic starter kit.

My original prototype has been living its best life 80 feet up in a tall tree since August 2024. So far it has proven to be extremely reliable with range only limited by line of sight!

SAFETY NOTE

In a followup Instructable I will demonstrate how to add a BMS protection circuit to the 18650 battery that comes with this solar buoy. The RAK board will function properly and charge the battery without a BMS circuit. However, a BMS is important to prevent overcharging or undercharging, which can damage the battery and create a fire hazard.

BMS chip examples: Linear style | Button style | Inline Plug

Impact-Site-Verification: 97b7c742-060b-40f1-9c8f-7e368a29df8b

Main body:

Solar net marking buoy light: AliExpress | Amazon | eBay

(Keep the waterproof housing, gasket, 18650 battery, foam inserts, and solar panels)

Electronics:

WisBlock Mini Meshtastic Starter Kit (RAK19003): Amazon | Rokland

20cm coax IPX to SMA pigtail adapter: AliExpress | Amazon | Rokland

RAK Solar connector cable: Amazon | Rokland

SMA antenna of your choosing (915 MHz for North America): AliExpress | Amazon | Rokland

Custom 3D printed bracket for RAK19003 board: Cult3D (Please consider purchasing my STL file!)

Sealing the antenna port and cap threads:

Clear UV cure resin, flexible soft type: Amazon

UV flashlight (any UV light source will work, including sunshine): Amazon

UV resin 3D printer curing light (overkill, but it works great): Amazon

PTFE gas line thread seal tape (thicker than standard white PTFE tape): Amazon

Tools:

A big wrench... recommended for removing the cap.

1/4 inch drill bit for the antenna port (drill press optional)

Silicone Caulk Remover and small blade to clean the cap threads: Amazon (wear gloves in a ventilated area, this is strong stuff!)

Soldering iron and solder

#1 Philips head screwdriver

Small wire cutters

One plastic drinking straw (bendy style recommended)

Your buoy will come sealed TIGHT from the factory for its original mission to survive in the open ocean.

Fortunately RTV silicone is no match for a big wrench. Congratulations on completing the most physically demanding step of this project.

To clean up the silicone, I like to carefully apply caulk remover solvent with a paper towel or Q-tip to the threads only. The solvent will cause hazing on the clear plastic if it touches other areas. Let it soak for a minute, then use a small blade or screwdriver to peel it off in pieces. A few blasts of compressed air will get rid of the final crumbs.

Remove the three screws attaching the LED circuit board to the tubular base.

Now pull everything out of the tube. I appreciate that engineers somewhere figured out how to use cheap foam inserts to simultaneously hold all the electronics perfectly in place whilst guaranteeing these things remain buoyant.

The battery connector is the same as used on your RAK board! STOP HERE.

DO NOT PLUG THE BATTERY IN YET! You must check the polarity to make sure it matches the RAK's input (positive red wire inside, negative black wire outside), otherwise you will release magic smoke from your board (ask me how I know).

This step is VERY IMPORTANT

You WILL damage your board if you plug in a battery with reversed polarity. Unfortunately the JST connectors have no industry standard for polarity, so you need to check. For a RAK WisBlock the positive voltage (VBAT) must be on the inside of the connector.

RAK19003 Datasheet for Reference

To reverse the polarity, you can use a small screwdriver or knife to lift up the plastic tabs of the battery connector. Pull out the pins (it should require no force if the tabs are lifted), swap their positions, and push the plastic tabs back down. Use caution not to short circuit the pins.

Remove the LED circuit board by cutting both the red and black wires as close as you can to the solar panel.

Do not cut the wires BETWEEN the solar panels.

Save the LED board for a different project.

No photo for this step yet -- I did not have a free hand while soldering.

Simply solder the red and black leads from your solar charging connector cable to the corresponding solder pads on the solar panel where you just cut the red and black wires in Step 4.

CHECK THE POLARITY!!! If you aren't using RAK brand connectors, make sure the red wire is on the inside of the solar connector, just like it was for the battery connector.

Carefully drill a 1/4 inch hole through the pointed end of the base. It doesn't need to be perfectly centered, just do your best.

Clear away any burrs and shavings as best you can.

Insert the barrel of your SMA pigtail through this hole from the inside of the tube. Fasten it on the outside using a tooth lock washer and nut that comes with the pigtail.

This part can get messy if you make a mistake, so plan ahead and take your time.

1) Clamp your tube vertically in a vice or use a tall drinking glass for support.

2) Bend and hold your straw at a point about 3/4 of the way up... a bendy straw works perfect for this.

3) Carefully fill the straw with UV resin up to the bend. Cap the opposite end of the straw with your finger.

4) Insert the straw all the way into the bottom of the tube. Take care not to touch the side walls.

5) Release your finger from the straw and allow all of the resin to drain into the base.

6) There is a ledge molded inside the buoy tube that is designed to abut the solar panels. Your goal is the fill the base up to that ledge. If you overshoot a little, no worries!

About the use of UV resin:

Low viscosity UV resin is inherently self leveling, electronics safe, and has a long pot life (unless you are building nodes out in the sun!). I'm using a "soft type" resin because I want it to flex with the case during thermal expansion to maintain an airtight seal.

When prototyping this project I initially tried using a self-leveling silicone "chip sealant" that was more viscous and had only a few minutes of pot life before it began to cure. It did work to seal the port, but the end result looked messy like hot glue.

This is a fun part!

Simply stick your UV flashlight into the opening of your tube and turn it on.

Wait a few minutes for the resin to cure. It will emit a distinct smell and the exothermic reaction will make the barrel of the SMA connector start to feel hot to the touch.

I also like to cure a bead of resin around the outer nut and tooth lock washer so they will remain sealed and not come loose.

During re-assembly, it is important to maintain a clear runway for your wires up along one edge of the tube. I like to orient everything so the wires run up behind the mounting lugs molded into the outside of the tube.

1) Slide the battery holder foam insert, with a round hole through it, back onto your battery. Position the foam just below the horizontal wires connecting the solar panels.

2) Trim a second piece of foam to be about 1 inch long and cut a slit lengthwise to create a path for your coax.

3) Position the coax into the foam slit and carefully fold the panels up like a triangular burrito.

4) Gently slide the solar panel burrito into your base tube. Pause a few times to tug on the coax and keep it taught.

5) Stop when the top edge of the burrito is just below the outer rim of the buoy tube.

1) Plug the Bluetooth and LoRa antenna connectors into your RAK board.

2) Attach an antenna to the SMA jack BEFORE plugging in the battery. In theory the radio can damage itself transmitting without a load. Just to be safe, attach an antenna first.

3) Plug in the battery and solar connectors.

3) (Optional) Insert the RAK board into a 3D printed mounting bracket and fasten it with a mounting screw from the RAK kit.

4) Insert the Bluetooth antenna into the slot on top of the mounting bracket. You might choose to use a drop of UV resin to glue it in place.

5) Using the base of the bracket as a tamper, continue pushing the solar panel burrito down into the tube until the solar panels touch bottom.

Before I designed a 3D printed bracket for this, I found it frustrating that the antenna connectors would frequently pop off while screwing the cap onto the tube. One time a board got itself wedged in at a weird angle and I accidentally bent and broke the board while unscrewing the cap. Not fun.

My bracket features a secure screw mount for the bottom edge of a RAK19003 board, a pillar to stabilize the USB port, Bluetooth antenna holder, and a safety tab to prevent the LoRa IPX connector from disconnecting. If you like my design, please consider purchasing a copy of my STL file.

Add two wraps of PTFE thread sealant tape to the threads of the tube and replace the gasket you removed in Step 1.

Carefully screw the cap back onto the tube until it makes a firm seal with the gasket. Stop if you feel anything binding or grinding (don't break a board like I did!)

Now fire up your Meshtastic app to initialize the RAK board and enjoy your new solar powered node!

There are any number of techniques to SAFELY run a throw line up and over a high branch of a tree to elevate your node. I've read about people using drones, air cannons, even casting it with a fishing pole! Personally I've had success using a giant sling shot to reach 80+ feet elevation. Preparing for a clean shot is the best method for success.

1) Lay your line out on the ground under your tree in big long rows zig zagging back and forth. Be careful to avoid sticks or plants that may snag your line as it shoots up.

2) Attach an 8oz throw bag to the leading end of your line and a second throw bag to the trailing end.

3) Nestle the 8oz throw bag into the slingshot basket and take aim at your target. I've found that a 60 degree vertical angle (steeper than 45 degrees) yields good penetration into a tree's canopy without overshooting into neighboring trees.

4) If you miss, drag the line back down and start over with with a clean lay of line.

5) Once you hit your mark, pull the line back towards you until the leading throw bag is up near your apex. Slowly release the line and maneuver it down to the ground as vertically as possible through the underlying branches.

6) Now switch sides and pull the trailing bag up towards the apex. Lower it back down as vertically as you can.

7) Remove both throw bags. Tie each end of the line to one of the lugs of your solar buoy. I like to use a taut-line hitch knot because it doesn't bind up under tension, which makes it easier to remove in the future.

NOTE: For RF performance it doesn't matter it the antenna points up or down. I like to point the antenna up so it hits fewer snags when I eventually lower it in the future.

8) Pull on your line to raise the buoy up into the tree canopy.

9) When you have reached your desired height, tie the loop around the trunk of the tree. I don't recommend using a ground stake or nearby objects unless you are very confident they are permanently anchored. When the wind blows and the tree sways, the tension on the loop could pull objects out of the ground and create a safety hazard swinging in the wind.

10) To bring the buoy down, simply untie the loop from your tree trunk and pull.

Big Shot Slingshot: Amazon (kit with line and throwbags) | Amazon (tool only)

Throw Bags: Amazon (8oz light weight for maximum altitude)

Throw Line: Amazon (Dyneema name brand) | eBay (generic UHMWPE cord)