IOB-I2C-MAX731x

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IOB I2C MAX7311/7318 based IO Expander

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Download IOB-I2C-MAX731x -
Download IOB-I2C-MAX731x.smt550 -
Download IOB-I2C-MAX731x_array.scr - Eagle SCRipt
Download MAX7311.pdf - Documentation
Download MAX7312.pdf - Documentation
Download MAX7313.pdf - Documentation
Download PCA9675.pdf - Documentation

 

IOB-I2C-MAX731x Version 1.0

First built: 2020-09

The MAX 731x series costs twice that of the MCP23017/PCA9555 expanders; for that price one gets support for up to 64x devices on a single I2C chain. V1.0 is an experiment in building a mechanically robust baseboard to support reliable wiring practices.

Schematic
Schematic
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Bot Silk
Board
Board
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Board
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Download IOB-I2C-MAX731x.gerbers.zip - Gerber Fabrication files
Download IOB-I2C-MAX731x.parts - Parts List (spreadsheet data)
Download IOB-I2C-MAX731x_array.gerbers.zip - Gerber Fabrication files
Download IOB-I2C-MAX731x_array.parts - Parts List (spreadsheet data)

 

IOB-I2C-MAX731x.bom

Parts Value Package Quantity Library Type/Feeder
C1 0.1uF 0603-CAP 1x SPCoast 19
R17 4k7 0603-RES 1x SPCoast NONE
BOARD CONNECTOR-I2C-EXPANDER I2C-EXPANDER 1x SPCoast PTH
LED16 G 0603-LED 1x SPCoast 3
IC1 MAX7311 TSSOP24 1x SPCoast NONE
U$1 OSHW OSHW-LOGO-L 1x SPCoast PTH
SW1, SW2, SW3 SPSTx4 EDG-04 3x SPCoast PTH

IOB-I2C-MAX731x_array.bom

Parts Value Package Quantity Library Type/Feeder
C1X11, C1X12, C1X13 0.1uF 0603-CAP 3x SPCoast 19
R17X11, R17X12, R17X13 4k7 0603-RES 3x SPCoast NONE
U$5X1 BOARD BOARD-TEMPLATE-IOB-I2C-3X1-ARRAY 1x SPCoast PTH
BOARDX11, BOARDX12, BOARDX13 CONNECTOR-I2C-EXPANDER I2C-EXPANDER 3x SPCoast PTH
FID-LR, FID-UL FIDUCIAL FIDUCIAL_1MM 2x SPCoast NONE
LED16X11, LED16X12, LED16X13 G 0603-LED 3x SPCoast 3
IC1X11, IC1X12, IC1X13 MAX7311 TSSOP24 3x SPCoast NONE
U$1X11, U$1X12, U$1X13 OSHW OSHW-LOGO-L 3x SPCoast PTH
SW1X11, SW1X12, SW1X13, SW2X11, SW2X12, SW2X13, SW3X11, SW3X12, SW3X13 SPSTx4 EDG-04 9x SPCoast PTH

Documentation

IOB-I2C-MAX731x

License: CERN Open Hardware Licence v1.2

Introduction

IOB I2C MAX7311/7318 based IO Expander

The MAX 731x series costs twice that of the MCP23017/PCA9555 expanders; for that price one gets support for up to 64x devices on a single I2C chain.

This board was originally produced to help me build control panels for my model railroad - I needed to connect many different buttons, switches and lights to an Arduino, and also connect the Arduino to a communications bus (Ethernet, CAN or Loconet), and I couldn't find anything that had both high IO point density AND visual feedback.

I started with a simple I2C based 32-pin Arduino IOShield with monitoring LEDs on each pin (Active-LOW inputs, LED is on when pin is grounded, writing a "1" to the port pulls it to ground). I was aiming to support up to the max I2C devices that can be used together, with the 8-bit board I2C-8574-IO (deprecated), that was a total of 8x boards with 128 i/o points.

The 7311 IO expanders used here will support up to 64 boards, with 1024 potential I/O points.

This latest design moves from overly generic and/or overly specialized designs to a generic design with daughterboards that encapsulate the appliance-specific buffering and logic. The benefits provided by these IOB boards include:

  • Improved I/O bank utilization (leftover capacity is now a multiple of 4-bit daughtercard instead of 16-bit I2C card...)
  • Riser height eliminates having to custom cut 3M track
  • Allows deprecation of cabling intensive signal driver IO4 and I2C boards
  • Allows custom circuitry to be added to Signal, Detector and Turtle drivers

Cautions

With several hundred IO loads, and up to 256 external breakout devices, a suitable power supply (or supplies) must be used.

In practice, a 3A 9-12VDC supply a good choice for most small to medium sized control points.

This supply needs to power the core processor, its direct IO loads, the I2C expander chain AND provide ~100mA to each IO4 device. Instead of relying on the Arduino's onboard regulated supply (which is only good for about 100mA itself), each board has its own regulator with a common supply feed that can handle up to 4A @ 12v. If more power is needed, the daisy chained power feed thru can be replaced with a per-board independent supply.

Specifications

This IO board is based on the MAX7311/18 16 bit IO Expander, mounted on a IOB Baseboard that presents a bank of 4x I/O personality boards (IOBs). The Baseboard contains buffered LED drivers connected to LEDs that show the status of the I/O lines in real time. They also contain the needed circuitry to drive / sense the appliances connected to them. See

Each board provides a latched set of 16x IO points, with each point being software selectable to be either an input or an output. The individual points are reasonably protected from the environment, and can sink 10 mA each (they are NOT current sources!) By using active low inputs and outputs, the effects of environmental noise are reduced - remote sensors only need to ground an I/O point to register activity.

Communication Protocol

Simple I2C 16-bit Reads and Writes:
uint16_t I2Cexpander::read7311() {
    uint16_t data = 0;
    Wire.beginTransmission(_i2c_address);
    Wire.write(REGISTER_7311INPUT);
    Wire.endTransmission();
    // Wire.beginTransmission(_i2c_address);
    Wire.requestFrom(_i2c_address, (uint8_t)2);
    if(Wire.available()) {
        data = Wire.read();
    }
    if(Wire.available()) {
        data |= (Wire.read() << 8);
    }
    // Wire.endTransmission();
    return data;
}

void I2Cexpander::write7311(uint16_t data) {
    data = data | _config;
    Wire.beginTransmission(_i2c_address);
    Wire.write(REGISTER_7311OUTPUT);
    Wire.write(0xff & data);  //  low byte
    Wire.write(data >> 8);    //  high byte
    Wire.endTransmission();
}

See I2Cexpander-lib for a more complete interface library.

Addressing

The address selection for the MAX731x is complex, as it uses 3x address pins, but adds SDA and SCL to the traditional “Vcc and Gnd” used elsewhere.

AD2 AD1 AD0 A6 A5 A4 A3 A2 A1 A0 ADDRESS (HEX)
GND SCL GND 0 0 1 0 0 0 0 0x20
GND SCL V+ 0 0 1 0 0 0 1 0x22
GND SDA GND 0 0 1 0 0 1 0 0x24
GND SDA V+ 0 0 1 0 0 1 1 0x26
V+ SCL GND 0 0 1 0 1 0 0 0x28
V+ SCL V+ 0 0 1 0 1 0 1 0x2A
V+ SDA GND 0 0 1 0 1 1 0 0x2C
V+ SDA V+ 0 0 1 0 1 1 1 0x2E
GND SCL SCL 0 0 1 1 0 0 0 0x30
GND SCL SDA 0 0 1 1 0 0 1 0x32
GND SDA SCL 0 0 1 1 0 1 0 0x34
GND SDA SDA 0 0 1 1 0 1 1 0x36
V+ SCL SCL 0 0 1 1 1 0 0 0x38
V+ SCL SDA 0 0 1 1 1 0 1 0x3A
V+ SDA SCL 0 0 1 1 1 1 0 0x3C
V+ SDA SDA 0 0 1 1 1 1 1 0x3E
GND GND GND 0 1 0 0 0 0 0 0x40
GND GND V+ 0 1 0 0 0 0 1 0x42
GND V+ GND 0 1 0 0 0 1 0 0x44
GND V+ V+ 0 1 0 0 0 1 1 0x46
V+ GND GND 0 1 0 0 1 0 0 0x48
V+ GND V+ 0 1 0 0 1 0 1 0x4A
V+ V+ GND 0 1 0 0 1 1 0 0x4C
V+ V+ V+ 0 1 0 0 1 1 1 0x4E
GND GND SCL 0 1 0 1 0 0 0 0x50
GND GND SDA 0 1 0 1 0 0 1 0x52
GND V+ SCL 0 1 0 1 0 1 0 0x54
GND V+ SDA 0 1 0 1 0 1 1 0x56
V+ GND SCL 0 1 0 1 1 0 0 0x58
V+ GND SDA 0 1 0 1 1 0 1 0x5A
V+ V+ SCL 0 1 0 1 1 1 0 0x5C
V+ V+ SDA 0 1 0 1 1 1 1 0x5E
SCL SCL GND 1 0 1 0 0 0 0 0xA0
SCL SCL V+ 1 0 1 0 0 0 1 0xA2
SCL SDA GND 1 0 1 0 0 1 0 0xA4
SCL SDA V+ 1 0 1 0 0 1 1 0xA6
SDA SCL GND 1 0 1 0 1 0 0 0xA8
SDA SCL V+ 1 0 1 0 1 0 1 0xAA
SDA SDA GND 1 0 1 0 1 1 0 0xAC
SDA SDA V+ 1 0 1 0 1 1 1 0xAE
SCL SCL SCL 1 0 1 1 0 0 0 0xB0
SCL SCL SDA 1 0 1 1 0 0 1 0xB2
SCL SDA SCL 1 0 1 1 0 1 0 0xB4
SCL SDA SDA 1 0 1 1 0 1 1 0xB6
SDA SCL SCL 1 0 1 1 1 0 0 0xB8
SDA SCL SDA 1 0 1 1 1 0 1 0xBA
SDA SDA SCL 1 0 1 1 1 1 0 0xBC
SDA SDA SDA 1 0 1 1 1 1 1 0xBE
SCL GND GND 1 1 0 0 0 0 0 0xC0
SCL GND V+ 1 1 0 0 0 0 1 0xC2
SCL V+ GND 1 1 0 0 0 1 0 0xC4
SCL V+ V+ 1 1 0 0 0 1 1 0xC6
SDA GND GND 1 1 0 0 1 0 0 0xC8
SDA GND V+ 1 1 0 0 1 0 1 0xCA
SDA V+ GND 1 1 0 0 1 1 0 0xCC
SDA V+ V+ 1 1 0 0 1 1 1 0xCE
SCL GND SCL 1 1 0 1 0 0 0 0xD0
SCL GND SDA 1 1 0 1 0 0 1 0xD2
SCL V+ SCL 1 1 0 1 0 1 0 0xD4
SCL V+ SDA 1 1 0 1 0 1 1 0xD6
SDA GND SCL 1 1 0 1 1 0 0 0xD8
SDA GND SDA 1 1 0 1 1 0 1 0xDA
SDA V+ SCL 1 1 0 1 1 1 0 0xDC
SDA V+ SDA 1 1 0 1 1 1 1 0xDE

This technical documentation is licensed under the CERN Open Hardware Licence v1.2

Tags: SPCoast eagle I2C