At work I research and design some cool things, then I send them off to a client and that's the last I see of it. Welp, I'm making a toy for myself based on the technologies I use everyday professionally.
This project is in the research/information gathering stages at the moment. A few things are clear though. The device must do these things:
- Have a very long battery life (multiple years)
- Be capable of sending sensor data long distances to a gateway of some kind
- Be small and discrete
- Be low cost
- Be an extendable platform to develop feature rich stuff with
From this list of requirements, things I'm pretty set on are:
- ESP32 PICO D4
- HopeRF RFM95 Radio
- 1 or 2 AA batteries (Lithium?) for power
* Optional PSRAM for fun?
This is my first project on Hackaday, and my first personal project that I've taken even slightly seriously. Let's hope I make it to Revision 1!
Initial design has begun, I would usually do my design in KiCad but I thought I'd like to give EasyEDA a try. I really want to try out the integration between EasyEDA/LCSC/JLCPCB because I've not used any of these services previously, and having a Cloud based EDA seems like a good idea for collab/public space projects.
Here are the two sheets for my current design. I may reduce this to one sheet in the future, depending on how much real estate I use. But I like to have some space to do lazy drag-selection when designing.
I want to be able to use the Top Level Sequencer (State Machine) on the SX1276 (RFM95), as well as the FSK and OOK modes. Some of the features I want such as Preamble/RSSI Detect require DIO3 or DIO4 so I at least need more DIO pins than the usual LoRaWAN stack for example. (DIO0-DIO2)
I'm torn between mapping all of the DIO pins to the ESP32 (The Input only pins from 34 to 39 are tempting), or just using some diodes here. I could also do a Wire OR, that can't be too bad right? I really need to think about the DIO more before I finalize that part of the design. Page 1 shows a tiny Diode array I found on Digikey (1.6mm square) but this could be precious real-estate later, they are also $0.50 each.
Another thing I do not have is a header to break all the pins out. I want something low profile (mezzanine connector?), and I'm also considering a castellated PCB. Still things to consider here.