The main problem related to FSO communication is atmospheric attenuation. To cope with such problem and maintain a dedicated connection, the transmitter power has to be adjusted continuously depending upon the weather condition of that particular time. Here we propose a design where we utilize the precipitation detection sensor and visibility sensor of ASOS. The weather conditions are detected using these sensors and some statistical data collected over time. Each condition provides some set of rules and equations which interlinks the power of receiver and transmitter. The transmitter if operated on such equation would yield the maximum efficiency. This results in power saving of the model. An automatic power device for FSO could be designed. In the below-discussed idea, we strictly restrict ourselves on atmospheric attenuation domain. Other factors like pointing Loss, Free space loss, Divergence loss are not taken into consideration. To take these issues into consideration, calculations have to be complex. While designing a real model, these factors would be taken as an important factor of attenuation too. Here Noise Equivalent Power and transmission power equation have been proposed which has visibility as a variable.