This instructables will show you how to make an alarm system that will beep a buzzer if you leave the fridge door opened for a long time to remind to you to close the door. All new fridges on the market have this option built in, but some may want to upgrade their old fridges.
This video shows the system in action:
- The Fridge Door Detector Alarm is easy to make - uses only 8 components including the batteries!
- Easy to set to your preferences for the time that the door is left opened - fully customizable!
- Cheap - less than 5kg potatos.
- Easy to install - installation means sticking a small box inside your fridge using sticky tape!
- Easy to maintain - change batteries just every four-five months!
- Encourages thinking and logic problem solving for the young electricians that will try to make it!
- Finally - saves electricity costs if you forget the door opened for a long time.
- 1st Oct 2012 - Added several schematics in steps 4 and 5.
- 4th Oct 2012 - Visually changed the code appearance in step 3.
- 7th Oct 2012 - Instructions made more clear in step 3.
- NEW: 8th Oct 2012 - Major changes in the ATtiny85 code: better power mode - enabled power save mode to reduce consumption. New code in step 3.
- NEW: 9th Oct 2012 - Added description for how to set the circuit sensitivity up. See step 7.
Step 1: The Idea
I use an ATtiny85 microcontroller which is easy to program with an Arduino if you have one ;) Than you can write the code that will suit your needs perfectly - for example one may want to hear the buzzer 2- seconds after opening the door ... or maybe 45 or 2 minutes - you decide!
Using a microcontroler minimises the use of external elements which saves you time and cost!
- ATtiny85 microcontroller
- Arduino Uno
- Prototyping board + wires
- Plastic box
- 180 kOhms resistor
- 0-100 kOhms variable resistor
- LDR - light dependent resistor
- Empty PCB to solder the schematic
- Board holder for the ATtiny
- Soldering iron
- Double sided sticky tape
- Cable cutters and knife