Particle driver for MCP23008 8-port I2C GPIO expander

Pinouts

One Side:

1 SCL (to Photon D1, blue)
2 SDA (to Photon D0, green)
3 A2
4 A1
5 A0
6 /RESET
7 NC
8 INT (output)
9 VSS (GND, black)

Other Side:

10 GP0
11 GP1
12 GP2
13 GP3
14 GP4
15 GP5
16 GP6
17 GP7
18 VDD (3.3 or 5V, red)

Note that the address lines are not biased so you must connect them to GND or VDD to set the address! Normally you'd connect all to GND to set address 0.

Same for /RESET, though you probably want to connect that to VDD to keep the device out of reset.

Here's my test circuit:

circuit

Important: Remember the pull-ups on the SDA and SCL lines (4.7K or 10K typically)! While many breakout boards like you'd get from Adafruit or Sparkfun includes the pull-ups on the board, you must add external resistors when using a bare MCP23008.

Using the Library

This library has an API that looks remarkably like the regular GPIO calls.

Initialization

Typically you create an global object like this in your source:

MCP23008 gpio(Wire, 0);

The first parameter is the interface. It's typically Wire (D0 and D1).

The second parameter is the address of the device (0-7). This corresponds to the value set on the A0, A1, and A2 pins and allows up to 8 separate MCP23008 devices on a single I2C bus.

On the Electron, you can also use Wire1 on C4 and C5:

MCP23008 gpio(Wire1, 0);

begin

void begin();

You must call begin(), typically during setup(), to initialize the Wire interface.

pinMode

void pinMode(uint16_t pin, PinMode mode);

Sets the pin mode of a pin (0-7). Values for mode include:

INPUT (default)
INPUT_PULLUP
OUTPUT

Note that it does not support INPUT_PULLDOWN, as the MCP23008 only supports internal pull-ups. Also, they're 100K vs. the 40K (-ish) pull-ups in the STM32F205.

digitalWrite

void digitalWrite(uint16_t pin, uint8_t value);

Sets the value of a pin (0-7) to the specified value. Values are typically:

0 (or false or LOW)
1 (or true or HIGH)

digitalRead

int32_t digitalRead(uint16_t pin);

Reads the value of the pin (0-7). This will be HIGH (true, 1) or LOW (false, 0).

If used on an output pin, returns the current output state.

getPinMode

PinMode getPinMode(uint16_t pin);

Returns the pin mode of pin (0-7), which will be one of:

INPUT (default)
INPUT_PULLUP
OUTPUT

pinAvailable

bool pinAvailable(uint16_t pin);

Returns true if 0 <= pin <= 7.

More Functions

The full documentation is available in the docs/index.html file or in the [browsable API reference](). This documentation is generated automatically from comments in MCP23008-RK.h using the Doxygen tool.

Example Programs

02-Really-Simple-Output

#include "Particle.h"
#include "MCP23008-RK.h"
 
MCP23008 gpio(Wire, 0);
 
void setup() {
    Serial.begin(9600);
 
    gpio.begin();
    gpio.pinMode(0, OUTPUT);
    gpio.digitalWrite(0, HIGH);
}
 
void loop() {
}

It's simple!

01-simple-gpio

This example outputs a square wave on pins 0 - 3:

GP0: 1000 ms. period (1 Hz)
GP1: 666 ms. period
GP2: 200 ms. period (5 Hz)
GP3: 20 ms. period (50 Hz)

This should result in the following:

Output

You can also connect a jumper from GP7 to one of those pins. It echoes the value on the GP7 input to the blue D7 LED on the Photon, so you can see the different frequencies.

03-interrupts

Uses the INT pin and a handler to be notified of changes in a GPIO on the MCP23008 efficiently.

04-interrupts-class

Uses the INT pin and has a handler as a C++ class member function.

Version History

0.0.4 (2021-02-01)

Added documentation

0.0.3 (2021-01-28)

Adds support for interrupt mode, to be further documented later.
Adds Wire lock() and unlock() for thread safety