The purpose I created this board is for evaluating a new feature that will be added in our company products

#1 – The Design

The feature of the PCB still same as the previous version, only several items are fixed

• Power Protection : Resettable Fuse, UVP
• Controller : STM32F103RxTx
• Flash Memory : 1MByte for Device Configuration
• Storage : Micro-SD Card using SPI Interface for data log
• Onboard Sensor : Sensirion SHT31 Temperature & Humidity Sensor using I2C
• Communication : ISL8483 RS485 Transceiver
• Communication : CP2102N USB to UART Converter
• Communcation : UART-TTL for Nextion Display
• Relay/SSR Driver using BJT Transistor
• ESD Protection : IEC61000-4-2 Level 4 (15kV)

#2 – Changes

– Add Thermal Reliefs

In the 1st version there is no thermal reliefs were added, especially for GND connection in TH parts, it caused headache when I try to assembly the part. The pad was directly connected to all GND on all layers. It causing the heat from soldering iron spreading throughout all PCB than focusing heating in the TH pad.

This issue was fixed by adding thermal reliefs in all TH pad, and all parts that connected into a big plane.

– Add Keep-out on L2 and L4

In the 1st version, there was an issue where the SHT31 sensor temperature reading increases gradually as the board was turned on, it caused by the solid there are no thermal relief in thermal-pad SHT31, and it directly connected to L2-L3-L4 solid ground plane, the heat transfered through that plane and making the SHT31 became self-heating. To fix this, in version 2, not only adding thermal relief, but also I add keep-out on L2 and L4 to minimize the connection between the sensor and the ground plane.

– Add Boot Mode Selection and Pull-Up Resistor on D+ Line (USB)

To make the boot mode selection easier, I add configurable jumper for both BOOT0 and BOOT1, also I add 1.5K Pull-up Resistor on D+ Line (USB) to make the USB work.

– Fix MicroSD Rotation

This is the most funny mistake in this project, in 1st version the MicroSD socket rotated incorrectly, make the microSD insertion is from inside area rather than outside. The rotation was fixed in the 2nd version.

– Fix Switched USB Data Lines

This is the runner-up of the funny mistake in this project, somehow I was incorrectly assign the D+ and D- data line into USB Type-C, this make the CP2102N IC doesn’t work in the 1st version. This issue was fixed in the 2nd version.

More data will be updated later