78L05Z 5V regulator IC 100uF 16V capacitor to filter the 5V dc supply to the 555 timer. 1000uF 35V capacitor to filter the unregulated voltage. The power supply is made up of the following parts: 4x 1N4002 diodes as a full wave rectifier to turn the AC from the train transformer into DC. There are 3 main parts power supply, timer, and output stage. The driver is actually a very simple circuit based around a 555 timer. Also if you need or want to you could make a bell from scratch you will need a spring loaded solenoid rated at the nominal voltage of your train transformer (~18V works for most O gauge stuff) and a bell or metal strip to strike. Other than that pick the bell that sounds best to you. Usually the 'front door' button will strike two different chimes where the 'back door' normally strikes a single chime.

Also note most bells have connections for two buttons. One that continues to ring when held down will not work for this project. Look for one that strikes a single note when the button is pressed and held down. Most have a display where you can test the bells. Easiest place to find these is in the doorbell isle of your local home improvement store. 1x dual screw terminal block (optional) 5x 1N4002 diode 1x 1000uF 35V electrolytic capacitor 1x 78L05z regulator (to-92 package) 1x 100uF 16V electrolytic capacitor 1x 22uF 50V electrolytic capacitor 1x 5.1k Ohm resistor 1/4W 1x 22k Ohm resistor 1/4W 1x NE555 timer IC 1x 8 pin dip socket 1x 100nF 50V ceramic capacitor 1x 120 ohm resistor 1/4W 1x 5mm red LED 1x 1k Ohm resistor 1x 2N3904 NPN transistor (to-92 package) 1x 10k Ohm resistor 1/4W 1x IRF640 N channel FET (to-220 package) hookup wire bell** Note for the bell you want a non repeating electro-mechanical type.

Most parts can easily be substituted with other values if needed. Note all the parts for this project were sourced off my workbench.

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