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16-Bit Digital I/O Card with Prototyping area



  • 16-bit Digital I/O card
    • MCP23017 Datasheet - Rev D
    • MCP23017... LOST TWO INPUTS
      • MCP23017 now a 14/16-bit expander, with two of the pins (GPA7 and GPB7) losing their input capabilities
      • The chips look the same, are called the same, and act mostly the same — if you don’t download the latest version of the datasheet (Revision D), you’d never know that there’s been a change
    • Strong library support for all major microprocessors for MCP23017
  • I2C Interface - Two Wire Interface
    • Can run at 400 KHz or faster
  • I/O Connector is inexpensive/standard DB-25
    • Fuse protected power output on DB-25 with jumper bypass
  • Large prototyping area
    • Connections at edges to DB-25 and GPIO lines
  • 24LC024 ODAS Personality EEPROM
    • Write Enable jumper protects against accidental writes
  • Open Data Acquisition System (ODAS) form factor (width is 95 mm)
  • Host connectors
    • Daisy-chain I2C connector
    • Address select jumper
    • Expandable I2C via I2C-RPT - I2C Repeater
    • Interrupt out/Card Present
    • Power connector (not required for minimal loads)
      • Reversible pinout for safety
    • I2C Termination jumpers for end of I2C chain
  • Power can be 3.3V or 5V
  • 95mm wide Open Data Acquisition System format
  • 6-32 Mounting holes

Prototyping Area

  • Large prototyping area
  • Ideal for through-hole ICs
  • Extra I/O Rows on both sides
    • One side connects to DB-25 connector
    • Other side connects to MCP23017 pins
  • Prototyping area in the center of the card with power/ground bus up the middle two pins
    • Easy connection to IC Power/Grounds
  • Silkscreen on both sides of the card
  • The above is the top two rows of the prototyping area
  • The pins on the far left are the pin number of the DB-25 connector (ex: Pin 24 is the top left, and pin 11 is in the next row).
  • The next 3 pins are bussed across to each other (the same row)
  • The next column has GND in all column positions
  • The next column has VCC in all column positions
  • The next 3 pins are bussed across to each other (the same row)
  • The far right pin has the DIGIO part connections (blank for the first row and Digital I/O pin 8 in the next point).


PROTO16-I2C-Rev3 CONNS.png

H1 - Power

  • Connector is optional since power can also be brought in via the I2C connector
  • Connector is 1x5 of 0.1" header
  • Connector is reversible
  1. GND
  2. PWR
  3. GND
  4. PWR
  5. GND

H2 - Interrupt/Card Present Flag

  1. GND
  2. INT0*
  3. CARD_PRESENT* (Low if card is present, should be pulled up by Host card)

H3 - Address Select

  • Sets the I2C offset address of the card
  • Three bit address A0, A1, A2
  1. A0
  2. A1
  3. A2

H4 - I2C

  • Connector is 2x4 of 0.1" header
  • Intended to be used for I2C daisy-chain of 4-pin cabling
  • Power can be attached to the connector or power can be provided to the card via the J1 power connector
  • May still want to connect ground
  1. SCL
  2. SDA
  3. VCC
  4. GND

H5 - EEPROM Write Enable

  • Install to allow writes to EEPROM
  • Remove to prohibit writes to EEPROM

H6 I2C Termination

  • Two of two position headers
  • Install headers in each position to terminate I2C line
  • There should only be one I2C termination and IDEALLY it should be at the end of the I2C line

J1 - DB-25 I/O Connector

  • Pins 1, 2, 14 are connected to Ground
  • Pins 12, 13, 25 are connected to Power
  • Pins 3-11 and 15-24 are connected to the Prototype area and are labeled on the PCB


There are quite a I2C drivers for every major microcontroller (Arduino, Raspberry Pi, BeagleBone, etc).

Arduino Drivers

Raspberry Pi Drivers

BeagleBone Black Drivers

ESP32 MicroPython Drivers

MicroPython Drivers

CircuitPython (MCP23017) Drivers

Raspberry Pi Pico

Personality EEPROM

Factory Acceptance Tests



Program Personality EEPROM

  • Menu driven
  • Auto-detects card
  • If test has been run before
Checking EEPROM for board type...Detected PROTO16-I2C board
R=Read EEPROM, W=Write EEPROM, T=Test DIGIOs, L=Loop Test, B=Bounce LEDs
  • Presents card type list for un-programmed EEPROMs
Checking EEPROM for board type...Company Mismatch
Select the board type
1 - DIGIO16-I2C board
2 - DIGIO-128 board
3 - OptoIn8-I2C board
4 - OptoOut8-I2C board
5 - DIGIO32-I2C board
6 - PROTO16-I2C board
7 - ODAS-PSOC5 board
8 - TBD board
9 - TBD board
Select board > 
  • Select board
Select board > 6
Writing EEPROM
Initializing eep buffer
len of buffer=96
reading block

Run I2C Loopback Tests

  • Test 'T'
Loopback Test PASS = 1, FAIL = 0

Run Bouncing LEDs

  • Select B
Bouncing LEDs - any key to stop
  • Use LED card

Rev History

Log of issues

Rev 3

  • Convert to Kicad 6
    • No schematic changes
    • New part libraries

Proto16-I2C Front-720pxV.png

  • Lots of Silkscreen changes
    • Array area more clearly delineated
    • Signal markings on rear of PCB

Proto16-I2C REAR-720pxV.png

Rev X2

  • No functional issues
  • Add A0 jumper for EEPROM and MCP23017
    • Verified works in Rev X2 (Kickstarter)

Rev X1

  • No functional issues



PROTO16-I2C Assembly Sheet