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:
- Meshtastic Ukraine with around 400 active nodes in the 433 MHz range.
- Austin Mesh in Texas, USA with weekly Friday check-ins (also available globally through the MQTT gateway).
- Iffy Books events and resources (including this incredible zine about Meshtastic).
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.
There is a great thread on the forum with several posts linking to the following resources that outline the effective power requirements:
- Meshtastic ESP32 airtime and current draws (Google Sheets)
- NRF52840DK+SX1262 Meshtastic airtime/current draws (Google Sheets)
- Meshtastic Power Consumption Tests (Google Sheets)
- How To Calculate Solar Panel and Battery Size (Google Sheets)
The general consensus appears to be that ESP32 powered devices without any bluetooth, screen or GPS attachments need 0.1W on average.
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).
And here is a close-up of the circuitry:
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).
- Document the measured power consumption of Heltec Lora 32 v3 when used as Meshtastic
- Document the device configuration for optimal performance.
- Document the INA219 usage and setup.