Building a Solar Powered Lora Meshtastic Community Network

Meshtastic is a wonderful project for creating decentralised text-based communication networks for local communities using low power (and low cost) Lora radios. Fun fact — the Meshtastic logo appears to reference the chirp modulation used by Lora.

The best way to learn about the project is to explore the forum, join the Discord server and the Reddit community, follow #meshtastic on Twitter, Instagram and on your ActivityPub network of choice, and find recent videos on YouTube.

There are various community efforts to build local networks already:

Network Map

Here is a map of all active nodes connected to networks that relay messages to the official MQTT endpoint. This map is created by a forum user and shared in this thread.

How to Build a Network

Following the learnings from the solar-powered Raspberry Pi security camera project, I want to build solar-powered repeat nodes (with REPEATER role) to place in high enough places to enable coverage for everyone in the area. Since repeat nodes are invisible to the network and can’t send health or sensor data, another node with SENSOR role would be connected to the same battery and would broadcast the health of the repeater node along with temperature and humidity at very long intervals for maximum power savings.

I’ve decided to use Heltec WiFi Lora 32 (v3) ($20, schematic diagram) for the repeater nodes as they use ESP32-S3FN8 for the main controller and SX1262 LoRa chip with an IPEX1.0 antenna connector. This type of connector is really practical for bringing the antenna outside of the enclosure as the larger SMA connector cables are usually harder to bend and require more space in the case.

It also features a TP4054 charge controller and a voltage divider connected to an ADC pin for monitoring the battery voltage which is useful for telemetry. I’ve yet to figure out if it has any over discharge protection.

It is reported that RAK4631 WisBlock Core (similarly priced) with the nRF52840 microcontroller and the same SX1262 LoRa radio uses significantly less power compared to ESP32 devices so it is probably a better choice for pure repeater nodes. However, I wanted something that is more universal with a screen and a case for this prototyping phase.

Power Requirements

There is a great thread on the forum with several posts linking to the following resources that outline the effective power requirements:

The general consensus appears to be that ESP32 powered devices without any bluetooth, screen or GPS attachments need 0.1W on average.

Solar Power

For the initial prototype I found this 4W (D4W) solar panel (affiliate link) with an integrated case for six 18650 battery cells. Using only three cells provides plenty of room for additional electronics like the LoRa board.

In general it is best to oversize the photovoltaic panels significantly to ensure that required charging voltage is reached even when there is low solar radiation (such as during winter).

4W solar panel with 18650 batteries for Meshtastic Lora nodes
In winter the charging power didn’t exceed 1W, though.
Charging circuit of 4W solar panel with six 18650 batteries and CL4056 for charge control and FP6276B boost controller for 5V output
4W solar panel with space for six 18650 batteries and a charging circuit.

And here is a close-up of the circuitry:

Charging circuit of 4W solar panel with 18650 batteries using CL4056 for charge control, FP6276B boost controller for 5V output and XB5352A for battery protection
Charging circuit of 4W solar panel with 18650 batteries using CL4056 (U3) for charge control, FP6276B (U4) boost controller for 5V output and XB5352A (U5) batter protection chip only for the solar input.

Battery Undervoltage Protection

The board appears to use XySemi XB5352A (datasheet PDF) battery management chip U5 (the SOT-23-5 component to the right of the “on” switch) which handles over-voltage (4.30V for VCU with 4.10V recovery VCL), over-discharge (2.40V VDL with 3.0V recovery VDL), over-current (3.2A IOV1), and over-temperature protection. However, this chip is placed on the solar input so there is no under-voltage or over-discharge protection on the battery side.

Configuring the Solar Powered Repeater

And here is the case fitted with Heltec Lora 32 v3 with INA219 connected to pins 41 and 42 (confirmed this with the Arduino Core library and the usage in the Meshtastic firmware) for measuring the battery voltage and current over time and reported over Power Telemetry. Note that simply attaching the device to the board will make the firmware use the INA219 bus voltage reading also for Device Telemetry (which is not documented).

Heltec Lora 32 v3 with an INA219 power sensor inside a 4W solar panel case

Next Steps

  • Document the measured power consumption of Heltec Lora 32 v3 when used as Meshtastic REPEATER.
  • Document the device configuration for optimal performance.
  • Document the INA219 usage and setup.

3 Comments

  1. Will Martin says:

    Hi Kaspars – this is Will from Austin Mesh – thanks for mentioning us! We have a meeting tonight and I’m excited to keep building out the network. We’ve found that it’s better to over-spec both the batteries and solar panels. Our “version 5.0” solar repeater uses a 12 watt panel and a 6,400 mAh battery (parts list is on austinmesh.org). One of the main problems with the RAK chips is if the voltage falls to a certain level it will put it into a permanent fault state, so it’s best to have a battery that cleanly shuts off power if voltage falls below a certain level. The simpleest way we’ve found to do this is with the Voltaic Systems iot battery packs. The other way we’ve tried is to use a an 18650 battery and use a cutoff chip that shuts power if voltage drops below 4.25v: https://www.etsy.com/listing/1421193059/10-li-ion-battery-protection-modules-pcm

  2. Jason Cameron says:

    One thing that I have been unable to find is where to find places to put the nodes. What are legal ways to place nodes in an area to get significant coverage? I live around Wichita, Kansas, which is relatively flatter than most areas of the country, but I’m unsure of how to go about setting up nodes to provide coverage? How do you go about it? Also, I’m using a “hide my email” which is why it looks strange, but this is to keep spam at bay, I hope you understand. I appreciate your time.

    • Kaspars says:

      That’s a great question. I’m also unsure about this here in Europe. I have the opposite problem of high density buildings and needing to place the nodes on roofs to allow for any decent coverage.

      The most practical examples I’ve seen on YouTube and the Meshtastic Discord channel are nodes higher up in mountains placed in wilderness or attached to trees.

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