Simplest yet durable light sensor.

[DerStrom8]

is there any other way to use the circuit without depending to the LDR?

The LDR is absolutely necessary if you want to sense light or dark. It changes resistance with the amount of light it receives, hence its name--Light Dependent Resistor

 

[kinarfi]

First glance, shouldn't the 10K and the 1K on the base be switched and don't you need 2 resistors for the feed back to work?
Jeff

 

[oishi]

what I mean is can the circuit work the same function if the LDR is replace with other component for experiment such as input AC voltage?

 

[Vectorxd]

 

[Reloadron]

what I mean is can the circuit work the same function if the LDR is replace with other component for experiment such as input AC voltage?

Yes, the circuit can easily be modified to work with a variety of sensors, for example a thermistor could replace the LDR for heat or cool functions. Yes, an AC signal could be applied resulting in an output of a square or rectangular waveform of constant amplitude. Since thjere is no mention of the amplitude, waveshape, or frequency that is about a generic answer as can be.

This link is a very good read on the use of comparators.

Ron