A Story

You are designing a security system to protect the fantastic home of Sarah Gotbucks. When triggered, the alarm system could send a message directly to the police or to her brother in LA. However, she wants several audible alarms as well, so the intruder will know there is trouble ahead, and flee rather than continue the break-in. Sarah wants the alarm loud on the outside speakers, but softer at interior locations. You can design the system to do this by controlling the voltage to each speaker, so Sarah can adjust the volume

You decide to use a low voltage power supply to control the whole system because sensitive electronic components operate on low voltage direct current. Futhermore it will be safer and easier to wire. The power supply for Sarah's security system should be capable of providing a variable voltage output. You begin your work by building a power supply which will convert dangerous 110v A.C.voltage into safe, variable D.C. voltage. The low volatge D.C. will be easier to use for controlling Sarah's complicated security system.