Figure 2 of a simple square wave generator. Two batteries are connected in series and drawn vertically. The negative of the upper battery is connected to the positive of the lower one. The junction of the two is brought out to a terminal to the right and labeled common. A single pole double throw switch has its upper stationary contact connected to the positive side of the upper battery. The lower stationary contact of the switch connects to the negative terminal of the lower battery. The movable contact (swinger) of the switch is brought out to a terminal on the right labeled hot.