Microcontroller

Instead of using ATMEGA328P, I use ESP32 for the main controller. But which type exactly? ESP32-PICO, ESP32-D0WD, ESP32-S2, ESP32-C3?

Most and previous ESP32 variants need USB to Serial converter to upload the firmware. Which is it pushed me to add serial converter chip on the board. It will increase the board size of course. Or I can leave serial breakout pad, so when I need to upload the firmware, I just need to connect it with the external serial converter. Good idea for saving space, but it will complicated in designing the external programmer, and also it is not convenience way in the firmware development phase.

Luckily, Espressif  already launch their chip that have internal USB CDC for upload and serial connection. And there is no significant difference in size. One of them is ESP32-S2 that also have a Wifi connection. So for the MCU I decided to use ESP32-S2 with a couple components to make it works as in datasheet.

Antenna

The PCB antenna is look like a quite cheap solution, but maybe it is not, especially for just prototyping. Because maybe it can't using HASL PCB, it need at least ENIG finishing PCB. I'm not expert in radio frequency, so please CMMIW. But even using PCB antenna is really a cheap solution, it required more space, right? So I jump to another solution, using SMD antenna.

There are so many SMD antenna manufacturer. Don't know which is the best. So I will randomly choose that fit to the board. If you have any experience of this, please let me know.

Display

I use same as Max.K design who created Chronio. LS013B4DN04. It's Sharp Memory Display which is a display between LCD and e-Paper. Simple answer why I use this LCD? because I already have it. Couple years ago I bought Texas Intruments Watch DevPack Addon Sensor Tag CC1350. So yes, it is the same display.

Real Time Clock

For the RTC, I came with RV-3028-C7 from Micro Cystal. It has 1%ppm, what a time accuracy! And the size is 10 times smaller than using DS3231. Don't know much about this RTC, never tried this. But already requested the sample from the manufacturer.

Battery Management

I use MCP73831T as a battery charger, and JST 2P 1.25mm for the battery connector.

Vibration Motor

I found a old cell-phone, and took the vibration motor. I think it will works without any issues.

FIRST MILESTONE

It is my first time using ESP32 chip and their required components. Plus it's a small smd chip. I usually work with 0603 package. Now I designed 0402 package. Hope it's not difficult to soldering by hand. 

Since there is a lot of new components for me, so I decided the first milestone is I just want to get the answer of :

• Is my minimum system of ESP32-S2 works?
• Can I program the ESP32-S2 without serial converter?
• Can I access Wifi?
• Is the RTC RV-3028 works?
• Is ESP32-S2 can drive the display?
• How about a simple buttons, it's works?

That is it!

Need to verify the design before I send the gerber file.