Working

RS485 via UART0 (Drive GPIO5 HIGH to enable output to A0/B0)

Green LED (GPIO4)

IO0-IO3 (GPIO 17, 18, 27, 22), all 5V logic

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If you are able to use serial or RTC from software, please let me know it!

Hardware details

The main components are:

  • U1 AHHCY6 DCDC regulator
  • U2 1117 3,3Volt Low Dropout Voltage Regulator
  • U6: TS3A24157 2-Channel SPDT Analog Switch
    • U7: SP3483, SO08, 3.3V Low Power Slew Rate Limited Half-Duplex RS-485 Transceiver
  • U3: WCH CH432T SSOP20 SPI dual UART
    • Y1: 22.1184 MHz Quarz (for U3)
    • U8 Sipex SP2323EE True RS232 Transceiver
    • U9: SP3483, SO08, 3.3V Low Power Slew Rate Limited Half-Duplex RS-485 Transceiver
  • U4 Epson RTC R8010, I2C und 2x IRQ
  • Q2: SOT23 702: 2N7002, N-Channel Mosfet
  • Q1 NPN Transistor 1AM = MMBT3904L
  • SS34 40V 3A Shottky Diode
  • U12 TXS0102DCUR FE NZ dual Level shifter (3.3V <-> 5V)
  • Diode CG_ TVS Diode 28V
  • BAT54C SOT23 Marking TL3
  • ESD Diode Marking AC: PESD5V0L1BA, Low capacitance bidirectional ESD protection diode SOD323

The IO Pins (on green terminals: 5V via 2x FE NZ) are:

  • green LED: GPIO4
  • IO0: GPIO17
  • IO1: GPIO18
  • IO2: GPIO27
  • IO3: GPIO22

RealTime Clock:

2channel SPDT switch:

  • COM1: UART0 TX
  • COM2: UART0 RX
  • IN1+IN2: via R34 to GPIO5
  • NC1+NC2: not connected (via R44 + R45 to second channel of U8, option: move FB1+2 to FB3+4 and remove R48, R50, R53)
  • NO1+NO2: SP3483 (RS-485) to B0/A0
  • Software:
    • set correct GPIO5 state
    • use Raspberry UART with any modbus library

CH432T SPI DUAL UART (RS485 and UART via Raspberrys SPI Interface and CS0)

The terminal blocks have the imprints

  • Power: 2EGT-5.08
  • Data: 15EGT-3.5