Programming Your Home Mike Riley

Prev Next

3.5 Writing the Web Mailer

Libraries for sending email directly from the Arduino abound. But these all rely on a stand-alone, dedicated email server providing the mail gateway. So even though the mailer code can be compiled into the Arduino sketch, the solution still relies on an intermediary to send messages from the Arduino to the email inbox of the intended recipient(s).

If you have access to an SMTP mail server that you can connect to for outbound message transmission, check out Maik Schmidt’s Arduino: A Quick Start Guide [Sch11]. His book supplies the necessary code and walkthrough on how to make this work. If you don’t have access to a dedicated SMTP gateway, we can use an Internet web hosting service that supports sending email from a PHP script.

Quite simply, because they are the most prevalent web-hosting server configurations. While I personally prefer a more modern web application framework like Django or Ruby on Rails hosted within a virtual private server (VPS), these technologies are not as universally supported by hosting providers compared to PHP. This wouldn’t be a problem if we hosted the web server within our own network (which we in fact do in Chapter 7, Web-Enabled Light Switch) or had access to a VPS. But given the setup configuration overhead associated with running both a web server and an email server that correctly sends outbound SMTP messages, it’s easier to go this route for our first project.

Sending email via PHP can be done with a single PHP file in a single line of code. That said, if you are interested in writing functional equivalents for your personal favorite web frameworks, go for it! If you succeed, please considering sharing your discoveries with the Programming Your Home book discussion community.

For this project, I have chosen a popular, preconfigured PHP-enabled web server with an SMTP outbound gateway, a configuration that popular website hosting companies like Dreamhost.net, Godaddy.com, and others offer to their customers.

The PHP script for sending email consists of only a few short lines of code. First, we will pass two parameters to the server: the type of alert to send and the recorded value of the flex resistor. Then we will compose a mail message containing the recipient’s email address, the subject, and the message contents. Then we will send the email.

WaterLevelNotifier/wateralert.php
	`<?php`
	`// Grab the type of alert to email and`
	`// the current value of the flex resistor.`
	`$alertvalue = $_GET["alert"];`
	`$flexvalue = $_GET["flex"];`

	`$contact = 'your@emailaddress.com';`

	`if ($alertvalue == "1") {`
	`$subject = "Water Level Alert";`
	`$message = "The water level has deflected the flex`
	`resistor to a value of " . $flexvalue . ".";`
	`mail($contact, $subject, $message);`
	`echo("<p>Water Level Alert email sent.</p>");`
	`} elseif ($alertvalue == "0") {`
	`$subject = "Water Level OK";`
	`$message = "The water level is within acceptable levels.`
	`Flex resistor value is " . $flexvalue . ".";`
	`mail($contact, $subject, $message);`
	`echo("<p>Water Level OK email sent.</p>");`
	`}`

	`?>`

The script calls the built-in PHP mail function that passes three required parameters: recipient(s), subject, and the body of the email. Yes, it’s that simple.

Save the code to a file called wateralert.php in the root web directory of your PHP server. You can test the script by opening your web browser and visiting http://MYPHPSERVERNAME/wateralert.php?alert=1&flex=486. The page should return a Water Level Alert email sent. message in the browser window, and a corresponding email message should appear in the defined recipient’s inbox. If it doesn’t, check your PHP server settings and make sure that your web server is properly configured to use a working email gateway. If you’re still not having luck with the message test, contact your website hosting provider to make sure your hosted solution is correctly configured for PHP email messaging.

By abstracting the delivery mechanism from the logic running in the Arduino, we can easily modify the message recipients and contents.

If you plan on having this PHP script provide a permanent service for Arduino message passing, consider adding a layer of security to the transmission signal so that only the Arduino can trigger the message condition.

This could be done by something as simple (though weak) as a password value passed in the HTTP GET parameters or by a more secure hash transaction that trades an authentication conversation between the Arduino and the web server. While adding a good security routine is beyond the scope of this project, it’s a good idea to incorporate such functionality so that your publicly exposed PHP email entry point isn’t abused by unwelcome connections.

Now that we have a working message gateway, we can hook up the Arduino to an Ethernet shield so the deflected flex resistor can talk to the rest of the world.

Prev Next