Instructables

Automatic blind hooked up to existing projector screen

Step 2: High level shifting ( 12V detection circuit with arduino )

The idea with this circuit is being able to "sense" with the Arduino weither the projector screen is going UP or going DOWN.

This circuit works like this :
- When current is provided on the base of the transistor, the current flows from Arduino 5V to GND, the Arduino INPUT is then HIGH.
- When NO current is provided on the base of the transistor, the Arduino INPUT is connected to GND, and then the INPUT is LOW.

I used two transistors (TIP122), one for each relay of the projector screen.

Now i am able to know when the projector screen is going down, or is going up.
 
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