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rpi-interface-board/README.md

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A Raspberry Pi-compatible PCB that extends the GPIO header with protected I/O, relays, and various features for versatile use in prototyping and project development.

Notes

interface-board issues noticed when soldering

  • digital in TVS diode footprint: dia is larger -> rotate one/space + 1.5mm drill
  • make diodes pwm larger hole
  • make pitch buzzer larger

interface-board issues at first test

  • analog leds vs terminal: CH0 and CH1 swapped (first, second terminal) -> renamed nets and added notes
  • analog leds vs terminal: CH2 and CH3 swapped (third fourth terminal)
  • CH1 and CH7 led on

Power supply board

FIXME: barrel-connector wrong polarity -> change housing (connected via wires) -> fix layout, schematic

RPI Specs (Zero, 3+)

  • Available (old) Pi: Raspberry Pi 2 Model B v1.1
  • GPIO
    • Low: 0.9V
    • High: 1.6V
    • Input current: 5uA
    • Input capacitance: 5pF
    • Output Current +-17mA
    • Pullup / Pulldown 50-65k
  • EEPROM GPIO0 GPIO1, leave unused

Feature Ideas

  • Temperature control
    • fan
      • auto turn on
        • temp sensor
      • turn on via gpio

Supply

  • Input protection

    • TVS
    • reverse polarity (polyfuse will trigger)
    • Fuse (5A polyfuse)
    • buffer

  • Pass through power supply

  • 3.3V, 5V, 12V, 24V Regulator

  • power by barrel connector (24V 5A)

  • power by usb [not allowed]

    • Switch between power by USB or power supply?

  • power by battery [dropped]

    • liion cell connector
    • BMS / charge controller
    • measure battery voltage
    • USB charging port

IO

  • Input

    • GPIO
    • wide voltage range (-1.7 to 120V)
    • TVS
    • reverse polarity (-1.73V max)
    • Low pass filter
    • Optocoupler input
    • ADC
      • external IC
      • multiplexer?
      • protection
      • scale input voltage
        • fixed inputs: 24V 12V 5V 3.3V
        • 20mA input
        • trim potentiometer?

  • Output

    • Relay
    • Mosfet
    • Optocoupler output
    • GPIO with over current protection
    • GPIO level shift (24V output)
    • PWM pins
    • shift register
    • DAC

  • LEDS indicate I/O state

  • Testpoints

  • ESD protection (tvs diodes uart, i2c...)

Bus

  • UART/RS485
  • RS232 Connector
  • I2C Pullup
  • SPI
  • CAN
  • Serial to usb (if Arduino)
  • OWB default GPIO4

UI

  • Input [dropped]
    • Buttons
    • DIP switches?
    • Temperature sensor
    • Encoder
    • Potentiometer
  • Output
    • Display [RPI display pending]
    • Buzzer
    • LEDS

Mechanical

  • Barrel plug (24V 3A supply)
  • Screw terminals
  • spring loaded?
  • pass through all pins?

Housing

  • RPI ports
  • banana sockets for power out
  • screw terminal exposed
  • buttons, leds: need to open up?
  • BNC? []

Other

  • Extension board with multiplexer
  • Breadboard compatible?
  • SD Card
  • Onboard MCU for standalone use?
  • separate bought MCU via i2c for additional GPIO, DAC, ADC in one

Questions

  • what analog input ranges (Voltage, Count)
  • RS232 RS485 SPI, IIC actually necessary? examples
  • CAN to second SPI?
  • 8x shift register outputs, 0.5A open drain or 7mA tristate
  • 2x PWM 30A enough?
  • max used PWM freq? (drop opto if >80khz)