An application with Comparator and photo transistor

Thread Starter


Joined Oct 12, 2011
I started some project and I though I could do it with informations from the internet, but it's pretty tough to do my self.
What i'm stuck on now is that I'll read led light with phototransistor and by using comparator(lm319N), I wanna output 5v when led is on and 0v when led is off.
where can I start this out from? I've seen many comparator circuit, but can't seem to do my self.
Please any help.
Last edited:


Joined Jul 17, 2007
Here is one simple schematic:

There really should be a 100 Ohm resistor in series with the LDR so that it won't get burned up in case the potentiometer VR1 is turned all the way down.