PCB changes

[jlin143]

Analog

• Move analog portion to a separate add-on board.
• On the separate board, include all necessary analog power (LDOs, voltage references, etc.). Input voltage 3.3 V from I2C VCC line. Consider TPS7A39 dual channel LDO.
  • REF 3V3
  • REF 1V65
  • +3.3 V semi rigid
  • -3.3 V semi rigid
• JST header for I2C connection to main board.

General Layout

• Change main board dimensions to 100mm x 50mm.
• Battery connector JST-PHR-02.
• Migrate battery board LDOs and solar input to main board. Pin holes and solder jumpers (?) to GPIO pins.
• Peripherals should try to have wires coming out of the short end.

I2C

• I2C VCC change from 5 V to 3.3 V.
• I2C second 5p JST.
• I2C each of the 2 onboard 5p JST connectors can toggle VCC via a GPIO pin. (2 GPIO required)

SDI-12

• Add 3.5mm jack.
• Consider future extensibility of UART for RS-485. Ability to disconnect UART from SDI-12 (and connect to external RS-485 module)?

Micro SD card

• Use chip select and card detect pins (connect to ESP32).

Wio-E5

• Replace Wio-E5 mini dev board with Wio-E5 module (use recommended layout from Seeed). Replace LDO with a higher efficiency LDO. Put a 2p male jumper after the LDO. The user can either use a female jumper to close the circuit and permit power to the system, or run a cable to an external power switch.
• Expose GPIO pins as male pin headers.

ESP32

• Pin out USB CDC. No physical USB port should be added, but a 3p male header (D+, D-, GND) should be provided for a USB connection for debugging.
• Remove ESP32_EN jumper.
• Remove ESP32 RST button (can be reset via STM32).