So i started thinking about an optical doorbell alarm.
In the apartment house i live we have an electric bell system. If someone rings the bell on the street, you can talk to him via the system. I think these systems are really common. So, i did not want to break the the device to make it fit to my needs.
Fortunatly the system has a nice feature: whenever someone rings the bell a little light on my device starts blinking.
Using my new knowledge about transistors from the book Make: Electronics, some thinking and research on the internet i found an easy and quick solution.
It's quiet easy to send the blinking signal from my corridor to another place. I just used a simple circuit consisting of an LED, a photoresistor, a transistor and two resistors. So i'll show you how to make it.
Step 1: Parts, Tools and Skills
- 1 little peace of perfboard
- 1 superbright LED (LED1)
- 1 transistor BC547 (T1)
- 1 resistor (value depents on your LED) (R1)
- 1 10k resistor (R2)
- 1 9V block battery and battery clip
- two long pieces of wire (depends on the way from the doorbell to the place where it should blink)
- black electrical tape
Soldering iron and solder
Hot glue gun
"Handy Hands" or "Third Hand" (if you like you could build your own )
- you should have basic soldering skills (Instructable How to solder )
- using your multimeter (Lady Adas Multimeter How to )
- some basic informations about LEDs (LEDs for beginners Instructable )
- reading circuit diagrams (see Instructable of aplauche)
Step 2: Building the Circuit
So you can start soldering the components to the prefboard. Follow the circuit diagram should be easy. Dont get confused, I used european symbols for resistors in the schematic. Dont connect the photoresistor, because it goes to the bell device in the next step.
Test your connections using your multimeter.
If you've done everything well you can go ahead to the next step.
Step 3: Preparing the Photoresistor
Solder one wire to one end of the photoresistor, and do the same with the other one. I used heat shrinking tube to isolate it, but you could also use electrical tape.
Attach it to your door bell device to the place where the light blinks after ringing. Use black electrical tape to protect the photoresistor from external light.
Run the cables / wires to the place where your LED should light up.
Tell somebody to ring your doorbell and test it.