Thank you VERY much indeed for your reply. Let me describe what I am trying to make. We are helping people with Dementia remember (or be reminded really) to shut their doors though a series of sensors that detect door close/open, swing and ambient temperature. I have made a little LED Hub on ESP32 with a RFM69 and version with RM95- commonly available low power radio and Lora Transmitters) and want the device to work:
- Point to point sending messages just to this hub
- LoRaWAN/TTN - so that as we make more of these then we can pass info via a web interface to the head nurse.
I want to make 50 of these and need to keep the BOM cost down. I already have one functioning using an ATMEGA328p MCU with the above radios and get a sleep current of 4uA. However I need to switch out the MCU and the STM32WL works in all other respects. There are three problems:
- Power - I want to use an CR2032 with minimum protection circuitary(buck/bost converter is lovely but expenive, hard to get hold of, and potential soldering nightmare) and achieve same if not better sleep current than 4uA. I know this is possible in spades with ST32WL but seems to come at the cost of additional components. The device only need to transmit and only receive once when it gets the downlink message at registration (for Lora version).
- Antenna - I want to use a chip antenna like to the one of the Generic Node.
- Board size - board must be 30mm x 35mm (space left for antenna marked in Grey is 23.5x10.5mm based on generic node)
So after minimising components, do I need to leave same space between the the STM32WL and start of board like in the Generic node - from top of MCU to start of antenna space is about 18mm, does this mean that I can’t design a chip an efficient antenna based design with my design constraints. Any help would be really appreciated.
As you can see from the image I only have 30cm - 18mm which leaves me only 12mm to place the MCU - so I am hoping that these space requirements are not a limitation and I can get help to find a way to have a more compact board.
I am looking at this reference design for a 2 layer board and if I can stick with 2 layers and achieve the above then that will mean that we can deploy to other care centres cheaply - somehow our solution is a combination of this design and the Generic node, looking for a way to the end of the rainbow! Thanks!