18. Door sensor

This example of digital input uses a door sensor to detect and report via the Internet two events: open door (Open) and closed door (Closed). It also sends the door status if requested by external event State.

With this sensor you can connect to the Internet doors, windows, drawers or anything that opens and closes. The sensor consists of a reed switch and a magnet. The reed switch contacts are of magnetic material and the external magnet acts directly on them (Figure 1).

1. Circuit

Connect the Door sensor as shown in Figure 1:

• a PIN to GND,
• other PIN to D3.

Note: PINs can also be inverted.

2. Sketch

Write a sketch K to define:

• the input connection: Door :: D3
• the events to send: Closed, Open
• the external event: State
• the commands: start, msg
• the rule for send the door status when asked through the external event State

Door :: D3

Closed = Door==0

Open = Door==1

State = 0

msg = [date,time,sn,Door]

start = [led=Door *]

State -> msg

or simply load the sketch in the workspace with the command

] load e18_door_sensor

Note

The following equivalences are valid:

• x == 0 <-> x == false <-> ! x
• x! = 0 <-> x == true <-> x

So you can also define:

Closed = !Door

Open = Door