Read out temperature from an LM75 via Arduino as I2C adapter

temp.php

#!/usr/bin/php
<?php

define('CHAR_ERROR', chr(0x1B));	// <ESC>
define('CHAR_ESCAPE', chr(0x5C));	// '\'
define('CHAR_ESCAPED_ERROR', chr(0xB1));
define('CHAR_ESCAPED_ESCAPE', chr(0xC5));
	
define('LM75_ADDR', 0x48);

// exec('stty -F /dev/ttyACM0 clocal cread cs8 -parenb -cstopb raw');

$fd = fopen('/dev/ttyACM0', 'r+b');
sleep(1);

function readUnescape($fd, $length) {
	$result = '';
	$escaped = FALSE;
	while ($length) {
		$data = fread($fd, 1);
		if ($data === FALSE) {
			throw new \Exception('Error reading device!');
		}
		if ($data === CHAR_ERROR) {
			throw new \Exception('Error signaled (1)');
		}
		if ($escaped) {
			switch ($data) {
				case CHAR_ESCAPED_ERROR:
					$result .= CHAR_ERROR;
				break;
				case CHAR_ESCAPED_ESCAPE:
					$result .= CHAR_ESCAPE;
				break;
				default:
					throw new \Exception('Invalid escaped character!');
				break;
			}
			$length--;
			$escaped = FALSE;
		} else {
			switch ($data) {
				case CHAR_ESCAPE:
					$escaped = TRUE;
				break;
				default:
					$result .= $data;
					$length--;
				break;
			}
		}
	}
	return $result;
}

function readReply($singleByte = FALSE) {
	global $fd;
	if ($singleByte) {
		$num =  1;
	} else {
		$data = readUnescape($fd, 1);
		$num = ord($data[0]);
		if ($num === 0) {
			return '';
		}
	}
	$data = readUnescape($fd, $num);
	return $data;
}

function writeCommand($cmd, $data = '') {
	global $fd;
	fwrite($fd, substr($cmd, 0, 1), 1);
	if (strlen($data)) {
		fwrite($fd, $data, strlen($data));
	}
	fflush($fd);
}

function identify() {
	writeCommand('I');
	$res = readReply();
	echo $res."\n";

	if ($res !== 'Arduino I2C-to-USB 1.0') {
		throw new \Exception('Invalid device');
	}
}

function temperatur() {
	writeCommand('A', chr(LM75_ADDR));
//	writeCommand('a');
//	$res = readReply(TRUE);
//	echo '0x'.dechex(ord($res))."\n";

	writeCommand('L', chr(0x02));
//	writeCommand('l');
//	$res = readReply(TRUE);
//	echo '0x'.dechex(ord($res))."\n";

	writeCommand('R');
	$res = readReply();
	if (strlen($res) != 2) {
		throw new \Exception('Invalid response from LM75!');
	}
	$msb = ord(substr($res, 0, 1));
	$lsb = ord(substr($res, 1, 1)) & 0x80;
	$lsb = $lsb >> 7;
	$msb = ($msb << 1) | $lsb;
	$temp = $msb * 0.5;
	return $temp;
}


identify();

while (TRUE) {
	$temp = temperatur();
	printf("%.2f °C\n", $temp);
	sleep(1);
}

fclose($fd);