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)