First, I want to advice all that I'm italian so I'm sorry for my bad english.
I wanted to activate a relay by calling a phone number: the easiest way to make it, was buying an GSM module, but it is very expensive! So I thought to resolve this problem by exploiting the fact that every mobile phone screen blink when a call is incoming.
For make this project i've used:
- Very old mobile phone
- Arduino Uno Rev. 3
- BC547B transistor
- LDR04 photoresistor
- 10Kohm resistor
- Recirculation diode
- Relay with 5V coil nominal voltage
- Small box that will keep the mobile phone