I didn't do any breadboarding at all, I just jumped off the cliff with this. I started by designing a 1"x1" PCB in EasyEDA with just the MCU and pin headers, and had five manufactured/assembled by JLCPCB to test the core of it. The first time I'd ever touched an ESP32 was when I got those PCBs in the mail and started trying to program them! It was really fun.
Once I'd proved it worked, I pasted that 1"x1" layout into a larger footprint, and added the sensor, power supplies, and batteries. Again, I had no real way to test any of the new stuff: I just iterated until I stopped finding problems to fix, then had them manufactured. A big part of the fun of this has been having to commit to a design without the ability to test: it really makes you think. I also enjoy the exercise of writing as much of the firmware as I can while the hardware is in the mail, then seeing how much actually works when it shows up.
In terms of bad decisions... I used builtin gpio pull-up resistors for I2C: it works, but the margin is very tight, it's just not worth it (and also means I can't put the ESP32 in sleep mode in some cases...). Wifi uses phase to encode information, so having no RF matching will impact its performance beyond the -6dB I mentioned in the README. The inductor/capacitor values are much larger than necessary. The routing of the I2C lines taking a huge bite out of the ground plane under the switcher IC is dubious. Using 1.5V alkaline batteries is nice because I don't have to worry about burning my house down... but I've gone through 200+ AAA batteries over the last year, and it feels very wasteful.
I learned most of what little I know about PCB design from this youtube channel, I can't recommend it enough: https://www.youtube.com/@PhilsLab
Once I'd proved it worked, I pasted that 1"x1" layout into a larger footprint, and added the sensor, power supplies, and batteries. Again, I had no real way to test any of the new stuff: I just iterated until I stopped finding problems to fix, then had them manufactured. A big part of the fun of this has been having to commit to a design without the ability to test: it really makes you think. I also enjoy the exercise of writing as much of the firmware as I can while the hardware is in the mail, then seeing how much actually works when it shows up.
In terms of bad decisions... I used builtin gpio pull-up resistors for I2C: it works, but the margin is very tight, it's just not worth it (and also means I can't put the ESP32 in sleep mode in some cases...). Wifi uses phase to encode information, so having no RF matching will impact its performance beyond the -6dB I mentioned in the README. The inductor/capacitor values are much larger than necessary. The routing of the I2C lines taking a huge bite out of the ground plane under the switcher IC is dubious. Using 1.5V alkaline batteries is nice because I don't have to worry about burning my house down... but I've gone through 200+ AAA batteries over the last year, and it feels very wasteful.
I learned most of what little I know about PCB design from this youtube channel, I can't recommend it enough: https://www.youtube.com/@PhilsLab