I gave this project a bit of thought. I want it to be portable and to have swappable ubiquitous power source. That is why it will be supplied from a power bank (micro USB). Most of the electronic parts that I want to use operate at 3.3V, so LDO (5V -> 3.3V) will be used. Dust sensor (PMS7003 - PM2.5/PM10) has 3.3V interface, but also requires 5V to operate. It has a power-down pin, but if in the future I would like t
o use one that does not have this functionality, I will implement a power switch to turn on/off power with a MCU pin. Reset button and user button are also handy. Some LEDs as a UI will also be added.
Data from the dust sensor is only valid with associated timestamp. RTC on the main board is going to be present with 3V coin battery backup - it should not lose time when power bank is being swapped or taken for charging. RX/TX serial console can be your best friend, so it will also be implemented.
As for the main MCU and radio link I have not chosen yet which technology to use. There are at least two use cases for me regarding this project. I want this device to sit tight on my balcony and log PM2.5/PM10 data every 15 minutes via Wi-Fi router to some website and on the other hand I want to take this device to some remote locations and be able to read real-time measurements on my mobile phone. So, I have decided to include only 2 rows of headers with power, serial and some other signals that will be routed throughout the PCB. That way I can use either BLE or WiFi solution as a switchable plug-in module.
Furthermore, I will include additional set of headers in case I would like to include some small extension boards, i.e. with additional sensors.
That is it. That is the system overview to fulfill MVP I have in mind. Let me know in comments what do you think about it. Next couple of evenings I will be spending on choosing electronic parts and creating a schematic. See you next time.
