How do I adapt a laser trip wire alarm. to work in reverse?

I need a schematic of a circuit that provides a 12v output when a laser is picked up on a phototransistor.  Essentially working in reverse of the laser trip wire alarm.

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lemonie6 years ago

What have you come up with so far & what bits do you have?

mightywetfoot (author)  lemonie6 years ago
A friend recommended this Figure 1 but the resistor R2 moved to V out. I am new to all of this so I am not really sure what I am looking at.

You want figure 2, that's the opposite function.
That looks like good stuff, do you need high current output?

mightywetfoot (author)  lemonie6 years ago
Nope, high current is not needed. Just something to trigger an Arduino Uno or similar microcontroller.
iceng lemonie6 years ago

You are going for 999 ? :-)