very simple thing that i need to know...

[ikalogic]

hi...
b4 i begin:
i'm very new to electronics, however i try hard, thx for your help!

so, the situation:
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I managed to build a small circuit that will light a led when there is light in the room, and shut it off when there is no light. the circit use a an ifra-red sensor from a mouse(that i use a light sensor) and a 741 op-amp in the inverting position to ampilfy the signal coming from the sensor.

The problem:
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i want to do the opposit: light the led when there is no light in the room, and shut it off if there is light.
i tried using 1 more op-amp to do that, and i succeded but the signal coming out from the secong op-amp is VERY low and i dont want to use a 3rd opamp to amplify this last signal!! i'm sure there is a more simple way of doing it (at least with only 2 op-amps)

thx a lot.

 

[panic mode]

It wouldn't hurt if you post schematic of what you have.
I guess you have photo sensor connected in series with a
resistor to the power source and 741 is reading voltage level
from the point where they are connected. I guess the simplest
way to reverse the operation of the circuit is to either swap
the inverting and noninverting input of the 741.
The other way would be to swap the positions of the
photo sensor and resistor it is in series with it.