Energy Saving Device: Easy Open Window Alert

Energy saving device: sounding alarm when a window is open for more than 5 minutes.

A lot of energy is wasted by left open windows during the winter. This can be avoided by alarming the user that the window is still open.

A simple device will sound an alarm if a window is open for more than 5 minutes. The open window is detected with a reed switch. The reed switch is toggled by a magnet mounted to the window.

What you need:

Bill of Materials:

ATtiny85 microcontroller + socket

Reed switch and magnet

Buzzer (passive) or loudspeaker

3 Resistors: 100 Ohm, 1 kOhm, 470 kOhm, 10 kOhm

1 LED

Battery with 3V to 4.5 V, i. e. 2 x AAA Battery holder

Tools:

Arduino IDE with ATtiny support: https://github.com/SpenceKonde/ATTinyCore

An ATtiny programmer; i. e. https://www.instructables.com/Arduino-Nano-as-Attiny-85-programmer-and-5-LED-POV/

Program the ATtiny with the attached program

Build the electronics, see schematic

Optional: ON/OFF switch between the battery and the electronics.

Optional: 3D print the housing (see attached .STL files)

Install the Device to a window:

Mount the Magnet to the window and the electronics close to it so that the reed switch is closed when the window is close and the reed switch is open when the windw is open

When you open the Window the LED should light up for two seconds to indicate that the window was opened.

If this is not the case please check the position of the magnet.

If the window is open the LED should flash every 4 seconds.

If the window is open for 5 Minutes, the alarm should go off (three beeps).

If the window is not closed, the alarm will repeated after 5 Minutes.

If the window is closed, or the alarm was repeated three times, the ATtiny85 will go to sleep.

Since the ATtiny is in sleep mode most of the time the circuit should run on 2 AAA Batteries for more than 2 years.