A black box has a pushbutton and two lights, labeled A and B. It is connected to a DC power supply. Light A is on, light B is off.

You push the button and while the button is pressed, light B is on and light A is off. You release the button and the lights switch back to the initial state.

You are told that the lights are ordinary 12 volt incandescent light bulbs. The pushbutton is an ordinary SPST, normally-open (NO) momentary switch. The circuit in the black box is made of passive components only.

Question:

Draw the circuit.

— Contributed by Tsuriel Assis.

Answer