Methods of forming an electronic device may include forming a gate electrode on a semiconductor substrate, and forming first and second impurity doped regions of the semiconductor substrate on opposite sides of the gate electrode. The system provides a control apparatus that regulates airflow to a closed environment, such as the mask of a breathing apparatus, to ensure sufficient breathing air for a wearer of such mask. The first pair of sheaves are located higher on the block than the second pair of sheave so that a portion of the first rope located between the first pair of sheaves crosses over a portion of the second rope located between the second pair of sheaves.