It has been in my design board for long now, to have my very own weather alert system at my home. Sure google gives me real-time information on weather, but 'WHY-NOT'.
I recently bought this solar lamp, and my curiosity killed the lamp circuit!
So I had a really cool looking lamp to implement my weather bug. The process of building a tiny Wi-Fi circuit which can be implemented inside this lamp and powered from a tiny solar cell, took me through a roller-coaster ride of Electronics 101.
My system constraints were pretty simple,
The circuit should be circular and tiny enough to fit inside the bulb.
The battery charge circuit should be able to power the Wi-Fi and sensor circuit at the same time the entire system's quiescent current should lowest possible.
Entire system needs to be designed around ESP8266EX - I am biased.
No matter what happens this time should not use Arduino :P
Hardware System Design
The above simplified block diagram is what I had in my head as my design. I wanted to put these blocks initially so that I know where to stop.
As I said this is a really tiny project with nothing fancy happening, pretty much all we will be doing is that to control the LED, get the weather status.
But the fun starts when you bring in the constraints and put yourself inside the first principles of electronics!
The real pain was populating all the components within the circular PCB of 27mm diameter. I wanted to keep the programming headers and utilize the ESP8266's GPIO to the max. So I had to go back and forth from datasheets to schematic design.
I know the above block diagram can seem pretty simple to have it inside those boxes, but putting every simple detail helped me while designing the schematics.
For example, the Wi-Fi Ant block and 3.3 volt blocks might seem redundant, but I had the following constraints for both of the blocks:
Wi-Fi antenna design needs to be efficient enough to fit into the smaller footprint of PCB at the same time the performance is not affected. Though there are various references available for ESP Wi-Fi ANT design, I had to try out different designs to find the right footprint for my use-case.
This article, helped me a lot in deciding if I need to eliminate the inductor from ESP's datasheet guidelines.
3.3V power supply - Finding the right regulator IC with least quiescent current and at the same time have enough juice to supply for all the components were tricky.
The discussion here, helped me to come to a conclusion.
Schematics and PCB
I used easyEDA to design my schematics and PCB design, because it is pretty simple to use and gets the job done. Not the professional approach out there, but for a software guy I think it was a valid reason to go-to.
The above is the final schematic design for the weather bug, it might not be the perfect design from a hardware point of view. Probably a few design errors, but it was purely designed from a hobbyist point of view. So please feel free to comment your thoughts/corrections and probably redesign the entire thing.
These should be the footprint for the final PCB and I wanted to keep the sensor and the power switch facing other way for better access.
It was really fun and painful to fit everything in best way possible and routing the PCB in this small footprint.
Of course this is purely a shoutout of what I am doing right now and wanted to post the designs. Because I realized there is no design out there with ESP8266EX with such a breakout configuration and I thought it might help someone who is looking for the same.
I will try to push my designs to my github you can always follow me to get notified with my updates.
Firmware - as I said I want to design this entire project around esp-idf so it might take some time as the PCB fabrication and testing the circuits might take up sometime. But, I will try to post my next update as soon as possible.