Interesting!
I'm thinking of building a small PCB for ballooning too.
But I most likely will shift the design decisions a bit:
- 2.4GHz LoRa for high-rate telemetry as reciving can recycle Wifi-Antenna gear. The Semtech SX128x chips are easy to handle.
- Low rate telemetry on 433MHz with a SX12xx or SX17xx.
In terms of chips most likely something around the STM32U series.
The company ePeas has very interesting energy harvesters. Not super cheap - but still affordable. They have special profiles for supercaps which are very resistant against freezing.
If you're going to use LoRa with an STM32, consider the STM32WL5x. It's an ST32L4 with an integrated SX12xx.
I have at least 10 of them in my lab :-) Thanks for the hint!
Hey! Yea I've been looking into energy harvesting a bit as well after watching this video: https://www.youtube.com/watch?v=TGbtzlWb-Kc
Generally the higher frequency you go, the lower range you get as a rule of thumb. It's also harder to design around higher frequency boards, though it's totally doable. That said, I'd love to see how 2.4GHz works out!
LoRa is absurdly robust.
Someone maxed out the ranging mechanism of the Semtech SX1280 with a 5dBi rubber antenna. He reached 60km with LoS. And there's a report of 90km in a ballooning project.
(https://github.com/StuartsProjects/SX1280_Testing)
In fact, it's so robust that even when your antenna is a piece of wire hanging off a GPIO of a microcontroller with absolutely no dedicated radio hardware, you can still get several km of range. Truly crazy stuff.
https://youtu.be/eIdHBDSQHyw
In a previous job I pushed an STM32WL5 on a custom frequency over a private satellite constellation with a relatively large yagi antenna. Over 70k km round trip :D
Interesting, thanks for sharing! I'm interested in creating some form of live video/image system, thanks for this!
The Semtech modems have several modulation modes which can be configured in great detail.. the datasheet is quite verbose about them.
The latest generation of chips (AFAIR not yet released) integrated a mode that allows them to receive on all LoRa speed grades in parallel. Bit like the existing LoRaWAN basestation ICs.
I remember reading a datasheet that one (already released chip) is also able to work on 144-146MHz. But that's not what standard Asia (ESP32+LoRa modules) offer. TTGO has AFAIR recently released a super new board that allows this band.
If you haven't seen it, you may be interested in https://www.areg.org.au/archives/210334