I needed to simulate a phone ringing that was capable of being triggered by an actor. Instead of using a speaker I figured my best (and most realistic) option was using the ringer from an old phone. As modern phones no longer use bells.
A phone line receives about 90 volts to trigger the phone to ring. However, applying just 12v directly to the bells coil is enough to trigger the arm.
To simulate the ring oscillation I applied a 555 timer
to a momentary push button.
