Some projects force you to learn, and Meshtastic is one of them.
Whether you live further out or in the city, you can be left without communication when things go wrong. Meshtastic is a mesh network that can be used by two people to share their locations and text messages all with no fees. Although it is not necessary, you can use an older cell phone and an app to send messages and view maps and the locations of other members of your mesh network. If you have one node tied to an internet portal (MQTT), you can communicate with the world.
Meshtastic.org is the place to start, and Discord is a place to learn more.
Placing a mountaintop repeater or router can expand your coverage, and as you will learn, some of the fun is sizing solar panels and figuring out what you will need to keep them alive and operating. Learning more about 18650 batteries, lithium-ion, VS other chemistries can also be fun, but I’m not here to teach that because there are a lot of better teachers available for free on Youtube and several other places.
What I can share is a little about the two places I plan to deploy a meshtastic network and why. I can also share some of the learning underway. One of my current concerns is that Lithium-ion chemistry can’t be charged below freezing, and I don’t see that anyone has provided an ‘on the shelf’ solution to this problem, so I will share my progress.
Once you get a stationary device up in the air, you can read the battery voltage and have some idea as to the solar gain of the day, you can also attach sensors and know the temperature and humidity for very little money.
A properly placed mountain repeater could give you hundreds of square miles of coverage, and the GPS location can be broadcasted to others publically, or you can keep all your messages encrypted and private among the group members you authorize.
My challenges, My learning.
When it is hard to keep a solar-powered repeater alive? I’d say during winter because the winter day is short and the sun angle is low. It’s rather amazing that the experts don’t agree on how you calculate the best angle for your PV panel in winter, but I’m learning it’s far steeper than I had thought. One calculation I came across is Latitude in degrees x .9 + 29. For the Area of Easton Washington, this equates to a steep 72 degrees, and as I look at the arch of the Sun’s travel, that looks about right for the season.
How does one get through 4 or 5 days of no sun? A lot of people are running one 18650 lithium-ion battery, which is about 3500 milli amp hours of capacity at the maximum. I found it easy to stuff three 27100 cells in my repeater case, this gives me about 15,000 mill amp hours. On a no-sun day, I see it takes about one percent of the battery’s rated storage capacity to keep it running. I haven’t had it up very long, but one day I had good sun for four hours and noted one hour of good sun would raise the state of charge to => than one percent.
My test device is currently programmed to be a router/client, it has been up for 8 full days, most of the time in a very poor position, but I moved it to a location where it can get good sun between 10 am and 1 pm, still not a good location, but the battery is at 70% charge which is the same as when I put it up. There’s been cloudy skies most of the time.
The PV Panel, and other potential problems?
A good portion of my experience with electronics and electrical has been power supplies or circuits to condition power for what you need to run are a big part of the project. The small Chinese solar panels you buy off eBay and Amazon often have quite a bit less watt capacity than advertised. I bought an Acopower 5W 12V panel that looks well made off Amazon, they claim to be a USA seller. 12 volts is a problem, the circuit I want to drive this time is the onboard charger of the RAK Wisblock, and it is about 5.5Volts max, or damage likely occurs. I best keep it at 5.1V for longevity’s sake.
Now we have some efficiency concerns, but I had to get this test router up in the air so I could start learning the basics of the configuration, I have the majority of this to learn.
To power the solar charger port, I ran the PV output to an LM2596s Buck converter, they are inexpensive, and the 5.1 volts I dialed in seems very stable. The converter has plus and minus leads in, and plus and minus leads out, I found the tiny connector I needed on Amazon.
Instead of a buck converter, there are tiny MPPT boards that promise more efficiency, and maybe my next unit will use one. I think I found a very nice box to build this repeater in, that too was found on Amazon. Since I’m especially happy with the box, I’ll share the link here. https://www.amazon.com/dp/B08P54XQK7?psc=1&ref=ppx_yo2ov_dt_b_product_details
The router sits on top of a 1 and 3/4 inch 20-foot long steel pole, I’ve had it for years, and I wish I knew where I could buy the next one.
The flaw in version one may be fatal, how will I correct the problem?
At first, I wondered if I was one of the few who worried about below-freezing and the destructive effect that charging could have on the lithium batteries in this device. I signed up for Discord, and eventually found the group discussing meshtastic. It didn’t take me long to find a group discussing exactly what I was worried about. I also noted they had already looked at sodium batteries and noted the need for a 2s battery management system (BMS) which isn’t on the shelf for sale yet. I read about Lithium titanate which can operate at far lower temperatures, but its chemistry produces a lower voltage similar to sodium, and you’d need two cells in series to work with the LORA radios that meshtastic uses. Two cells wired in series need to be balanced, and that is the primary job of a BMS.
So what to do? I think the parts will be on the shelf at some point, but we need some type of solution now, we just can’t let the batteries charge below freezing. Part of my approach is a lot of battery capacity, and then cranking down some of the unnecessary broadcasts. I don’t need the device reporting its location, nor do I need it telling me it’s alive every 15 minutes, cutting back on these broadcasts conserves battery.
I have not read of the approach I am taking, but I doubt I’m alone. As you read my plan, you might ask why is this guy using inefficient heat-producing parts. There’s a reason.
I plan to use the temperature and humidity sensor from Rokland.com, I’ll add it to the WisBlock, and our unit will know when it’s about to freeze. Rockland supplies the library you need to drive the sensors they have available, it should be easy to add a line or two of code to toggle a pin to a low state so we can use it to shunt the output of the buck inverter WHEN the temperature is 33F or below. I plan to cut copper foil so I can wrap it around the three Lithium cells and then use thermal conductive tape to attach both a TIP120 or its complement, and a 5-watt resistor to the copper foil.
When the temperature is below freezing, the I/O pin will saturate the base of the transistor and any energy the PV panel makes will generate heat inside the case, the transistor might add a little heat as the foil around the cells is its heat sink, the 5-watt resistor is the load and the main heat source which is also heating the cells directly. The resistor is sized to allow the PV panel to operate at about .28 amps and that’s what the manufacturer claims is the sweet spot. The buck converter is also inside the case, and its tiny losses are also helping to warm the inside of the box. The box is painted a flat black, and it faces south. There’s a thermal break between the box and the steel pipe.
When the sun hits the panel, all the PV energy is shunted away from the solar charger until the temperature rises to the setpoint. When this happens, the program changes the state of the I/O pin, the shunt is removed, and charging hopefully begins. During both charging and discharge, the battery produces some heat internally, and this all helps to keep the battery above freezing.
The test unit has been up for 8 full days now and there’s been only a few hours of good sun. This particular radio is very efficient, it lacks a GPS receiver, but it is built for a fixed position and doesn’t need it, another load we don’t need to drive. Right now it’s 9:20 PM, and the unit is at 69% charge, we’re down one percent, and one hour of the sun can put us back to even. Both sites where I plan to put repeaters/routers have way better views of the sky and significantly more sunny days, Cowiche borders Yakima which has an average of 300 days of sun. this is twice what Kent Washington gets where this test unit is set up.
what will I do with this mesh network? One of the first applications will be to monitor my solar plant, and to run the solar power irrigation system, I have trees planted, and they need to get through a potentially dry and hot spring and summer. if you can send a message and toggle an I/O pin, you can do most of what needs to be done.
Here’s one of the inexpensive pocket radios sitting on my desktop.
Here’s my parts list minus the mods to shunt charging at freezing, which is in the works.
High-Performance Meshtastic Router
Following parts from Rokland.com
RAK Wireless WisBlock Meshtastic Starter Kit US915
5.8 dBi N-Male Omni Outdoor Helium 915 MHz Antenna (Large Profile 32″) for RAK Miner 2 Nebra SenseCap M1 & Bobcat Hotspots
RAK Wireless RAK1901 Temperature and Humidity Sensor Sensirion SHTC3 PID: 100001 2-PACK
Following from Amazon
Otdorpatio Junction Box IP65 Waterproof ABS Plastic Electrical Project Case Power Junction Boxes, Project Box with Fixed Ear Black 4.53×3.54 x2.17 inch (115 x 90 x55 mm)
ACOPOWER Solar Panel 5 Watt 12V Black Monocrystalline High-Efficiency Module Off Gird PV Power with Solar Connectors for Battery Charging Path Light
wlaniot IPX/u.fl to N Type Female Pigtail Cable (6″ RG178 for PCI WiFi Card Wireless Router Gateway External Antenna etc.
Visit the Superbat Store
AZDelivery 5 x Compatible with LM2596S DC-DC Power Supply Adapter Step Down Module Compatible with Arduino Including eBook
Babaobox 10pairs 24AWG JST ZH1.5mm 2PIN Micro Electrical Male and Female Connector Plug with 150mm Wire Cables
smseace 30PCS JST ph2.0 Connector Female and Male jst ph2.0 Wire Cables 100mm jst ph 2.0 Connector kit
RioRand XT60 Drone Connectors (5 Pair)
Bistook 21700 Battery Holder Box Case for PCB Projects, 4-Pack, 4-Slot Each
Other parts you need:
1 3/4 inch steel tubing for a mast, mine is 20 feet long.
All the best,