Battery Backup System for Large Aircraft.
http://www.uoguelph.ca/~antoon/gadgets/backup.htm
http://ourworld.compuserve.com/homepages/Bill_Bowden/page4.htm#ps5.gif
It came in handy for many projects that were powered from 120 VAC
http://www.imagineeringezine.com/PDF-FILES/variac.pdf
produce a fully isolated and regulated 5 volts @30ma from the 120vac power line.
http://www.imagineeringezine.com/PDF-FILES/acdc1.pdf
A simple way to see if a fuse has blown without removing it from its holder.
http://www.mitedu.freeserve.co.uk/Circuits/Power/fusemon.htm
emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time. No direct connection to the internal wires of the power cord is needed. I also included a low battery voltage monitor.
http://www.imagineeringezine.com/PDF-FILES/cordalm1.pdf
This circuit produces a short beep once each minute. It is powered directly off the 120vac power line to remind you that a device connected to the circuit is turned on. It is simple enough to be packaged inside a small plastic box. It might be ideal for c
http://www.discovercircuits.com/PDF-FILES/beeper2.pdf