The Internet of things

Kim and Philip are on their way to Kim’s place. - Oh, I must buy milk. My fridge says that .. we’re out of it. - What, how can your fridge do that? - Here is Kim's kitchen and there is the fridge. Kim always has the milk on the bottom shelf in the fridge door. And here is an LED and a small device that detects light, a light sensor.

The light sensor is part of a small computer: a microcontroller. Kim has attached the LED to one end of the shelf. It is connected by cables to the microcontroller at the other end of the shelf. When there is a milk package on the shelf between the LED and the light sensor, the light is blocked. Then the light sensor sends a lower value to the microcontroller.

But if there is no milk package on the shelf.. ... the LED shines directly onto the light sensor. The light sensor sends a higher value. Kim has programmed the microcontroller to send information about the light sensor's value - via a wireless connection, Bluetooth - to Kim's computer. The computer is in turn programmed with this code: If the light value is higher than 100 send an email to Kim's phone.

Kim's computer is connected to the internet. The email goes from the computer to another computer on the internet that receives and sends emails, a mail server. Then Kim's phone picks up the email from the mail server. And that’s how the fridge tells Kim to buy milk. Kim has used a sensor and the network of computers to get the information needed to know when there is no milk.

The refrigerator has been connected to the internet. Kim’s fridge is part of the Internet of Things. - Aha that's why your fridge can tell you when there is no milk. - I have more plans. A surveillance system that checks if anyone enters the house, a microwave oven that warms a pizza just before I get home, a ... - Calm down Kim. Maybe you who are watching can think of more things that can be connected to the internet. - Socks that sort themselves?