settermjd/php-i2c-extension

A Zend Extension for php to grant access to an existing i2c bus on a linux device (Raspberry Pi and for example the ADS1x15)

php i2c extension

I've created this extension to get access to the i2c bus on my raspberry pi.

Installation

$ cd ~
$ git clone https://github.com/tasoftch/php-i2c-extension.git
$ cd php-i2c-extension
$ phpize
$ ./configure --enable-php-i2c
$ make
$ sudo make install

This compiles the source on your machine.
Next find the php.ini file

$ php --ini

Will list scanned ini files.
Add the following line to that php.ini file: extension=php_i2c

<?php
var_dump( extension_loaded('php_i2c') ); // Should be true

Usage

The extension adds five function to the global scope:

1. i2c_open
   This opens the device bus.
2. i2c_select
   This selects an address of a connected chip.
3. i2c_read
   Reads data from the i2c bus.
4. i2c_write
   Writes data to the i2c bus
5. i2c_close
   Closes the bus.

Example

I've tested with a Raspberry Pi Model B 3+ and the Adafruit ADS1115 analog to digital converter. It's default i2c address is 0x48.

<?php
$fd = i2c_open("/dev/i2c-1");
i2c_select($fd, 0x48);

for($e=0;$e<30;$e++) {
    // Read for 30 times the value between channel AIN_0 and GND, 4.096 V, 128 samples/s
    i2c_write($fd, 1, [0xc3, 0x85]);
    // Wait for conversion completed
    usleep(9000);
    i2c_write($fd, 0);
    $data = i2c_read($fd, 2);
    
    $value = $data[0]*256 + $data[1];
    printf("Hex: 0x%02x%02x - Int: %d - Float, converted: %f V\n",
        $data[0], $data[1], $value, (float)$value*4.096/32768.0);
    
    usleep(500000);
}

i2c_close($fd);

Usage PHP

The package also contains a php wrapper class for i2c.

$ composer require tasoft/php-i2c-extension

Please note that the composer installation does not compile the extension!
For compilation use the installation guide described before.

Now the same example can be rewritten as:

<?php
use TASoft\Bus\I2C;

$i2c = new I2C(0x48, 1);
for($e=0;$e<30;$e++) {
    // Read for 30 times the value between channel AIN_0 and GND, 4.096 V, 128 samples/s
    $i2c->write16(1, 0xC385);
    // Wait for conversion completed
    usleep(9000);
    $i2c->writeRegister(0);
    $value = $i2c->read2Bytes();

    printf("Hex: 0x%04x - Int: %d - Float, converted: %f V\n",
        $value, $value, (float)$value*4.096/32768.0);
    
    usleep(500000);
}