A simple observer implementation.

observer.php

<?php

interface Observable 
{
    public function callback($event, $value);    
}

class WeatherDashboard implements Observable
{
    private $temperature;
    private $airSpeed;

    public function showStats()
    {
        echo "Current Temperature : ", $this->temperature, PHP_EOL;
        echo "Current Air Speed   : ", $this->airSpeed, PHP_EOL;
    }

    public function callback($event, $value)
    {
        if ($event == "temperature-change") {
            $this->temperature = $value;
        }

        if ($event == "airspeed-change") {
            $this->airSpeed = $value;
        }        
    }
}

class TemperatureMonitor
{
    private $temp;
    private $dispatcher;

    public function __construct($dispatcher)
    {
        $this->dispatcher = $dispatcher;
    }

    public function getTemperature()
    {
        return $this->temp;
    }

    public function setTemperature($temp)
    {
        $this->temp = $temp;
        $this->dispatcher->notify("temperature-change", $temp);
    }
}

class AirSpeedMonitor
{
    private $speed;
    private $dispatcher;

    public function __construct($dispatcher)
    {
        $this->dispatcher = $dispatcher;
    }

    public function getAirSpeed()
    {
        return $this->speed;
    }

    public function setAirSpeed($speed)
    {
        $this->speed = $speed;
        $this->dispatcher->notify("airspeed-change", $speed);
    }   
}

class Dispatcher
{
    private $observers;

    public function register($event, Observable $observer)
    {
        $this->observers[] = array($event => $observer);
    }

    public function notify($event, $value)
    {
        echo "Got notified about event: $event with value: $value", PHP_EOL;

        foreach ($this->observers as $key => $observers) {
            foreach ($observers as $observer) {
                $observer->callback($event, $value);
            }
        }

    }
}

$wd = new WeatherDashboard();
$wd->showStats();

$dis = new Dispatcher();
$dis->register("temperature-change", $wd);
$dis->register("airspeed-change", $wd);

$tm = new TemperatureMonitor($dis);
$tm->setTemperature("10 c");

$asm = new AirSpeedMonitor($dis);
$asm->setAirSpeed("30 knot");

$wd->showStats();