This circuit will keep the battery for a train mounted camera charged and can shut the camera off after a few seconds when power is no longer applied to the track.
The circuit is designed for DCC systems. The battery is essentially used as a large capacitor with a built in zener diode. This is an inefficient but cheap way to control the voltage.
The battery controls the voltage to the camera as any current passed through R1 that is not used by the camera is shunted through the battery and keeps it charged for use if the track power is interupted.
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.
18 March, 2017