74HC155 (Dual 2-to-4-line Decoders/demultiplexers) irf620n 3 to 5V power and

3 to 5V power and I/O

Logic Diagram

but also can use the digital pin of Arduino to power on and reset the SIM900 module

Supply voltage: 5V(4

Detector type: phototransistor

74HC155 (Dual 2-to-4-line Decoders/demultiplexers) irf620n 3 to 5V power andDescription This circuit features dual 1 line to 4 line demultiplexer with individual strobes and common binary address input. When both sections are enabled by the strobes, the common binary address inputs sequentially select and route associated input data to the appropriate output of each section. The individual strobes permit activating or inhibiting each of the 4 bit sections as desired. Data applied to input 1C is inverted through its outputs.