August 18th

This is honestly my first journal entry. First hackclub project.

I started my day by researching what kind of hardware Meshtastic nodes generally use.

I looked at bunch of brands like heltec, lilygo, and seed studio.

Each board usually has

microcontroller (built-in wifi or bluetooth or both)
LoRa module (such as sx1262 or sx1278)
antenna connection and antenna
USB-C
display

and it usually runs on a battery or solar power.

Some nodes are used for tracking, so they have GPS modules.

Some nodes are used for monitoring, so they have sensors for temperature, humidity, etc.

For my node I decided it to be an off-grid messaging device so I would like it to have gps and be pretty low-power but also being able to be charged via USB-C from a powerbank.

Now coming to the choice of parts I figured there are 2 main ways to go:

Use a bare chip or SoC (system on a chip)

ESP32-C3 - less powerful than S3, single core risc-v (wifi, bluetooth)
- cheap and simple, less pins too
ESP32-S3 - more powerful than C3, dual core xtensa lx7 (wifi, bluetooth)
- more expensive, more pins
nRF52840 (bluetooth)
- really low power, but no wifi

Use a module (pre-built with a SoC and other components)

ESP32-C3-WROOM-1
ESP32-C3-MINI-1
ESP32-S3-MINI-1U
HT-CT62 (built-in esp32-c3 + sx1262 lora transciever)
- not a lot of pins but seems like a really good fit
nRF52840 module like Raytac MDBT50Q

The thing is if I go with first option, I would need to add a lot of things myself like decoupling, crystals, rf antenna ciruitry, and layout around the chip which is not ideal since I want to build a quick prototype and it’s basically my first RF project.

So really I should just decide between choosing esp32-c3-wroom-1 or ht-ct62 (or nRF52840 module).

I think for now ht-ct62 is the best option since it has a built-in esp32-c3 and sx1262 lora transciever, and is relatively cheap.

SX1262
SX1276
SX1278
RFM95

so 127* are the older gen transceivers and 126* are the newer gen transceivers.

and RFM95 is a module that uses older sx1276 chip.

Since I’m going with HT-CT62, I don’t need to add any of thse because ht-ct62 already has a built-in sx1262 lora module.

Now Lora radios use different frequencies and I figured that US/Canada uses 915 MHz which is part of the license-free ISM band.

Turns out there are many ways to classify radio communication.

By frequency like high frequency (HF), medium frequency (MF), or low frequency (LF).

By radio services like amateur radio, general mobile radio service, family radio service, and citizens band.

And it’s crazy that amateur radio can travel thousands of miles without satellites, repeaters, intermediate nodes or cellular towers. This can happen because the wave is launched at an angle and when it hits the ionosphere it is refracted back to Earth instead of only traveling line of sight.

Going a bit further into research I found a reticulum network - a pretty interesting project which is a secure decentralized communication network which allows
creation of independent local and wide area networks. Pretty cool!

Back to the project. I decided to add to the board standard usb-c, reset button, antenna, gps, and maybe oled.

Oh and also I want to add 18650 battery since I want to run the board on battery power and not just usb power.

So in this session I:

researched about mcu vs module
learned about reticulum network
read about different radio transceivers and modules
discovered for myself a lot of interesting things about radio communication
decided to use HT-CT62 as my radio module for the project