electret microphone

my microphone gives an output as

843 842 842 842 842 843 843 843 843 843 843 843 843 845 843 842 843 843 842 841 under normal conditions without opamp.... and when i clapped "very near" to microphone,then its output is about 800-840.... so that i m able to blink an led accordingly........... it works well.... but i want to increase its range of sound detection......and how to read readings from opamp,and what type of value it gives?? plzz help

The circuit at the end of the first page of this datasheet looks like what you need. It has a gain of 100 and should be a definite improvement! - a low-voltage rail-to-rail opamp such as the one in the datasheet is advised for 5V operation: http://www.stanford.edu/class/ee133/datasheets/LT1677.pdf

Linked from the Arduino Playground http://www.dtic.upf.edu/~jlozano/interfaces/microphone.html

how to give pin4 a -1.5v. and what type of reading this amplifier gives to arduino, digital or analog?...and how to analyze that... is it possible with LM358 op-amp??