These circuits allow an ON-ON type DPDT toggle switch to control a twin coil switch machine motor. The handle of switch can then be used to indicate the route selected. The circuits are also able to control LEDs that could be used to indicate the selected route.
The main disadvantage of these circuits is the cost of two large electrolytic capacitors per switch machine. This could be offset by bulk or surplus purchases of the capacitors.
The size of the capacitors depends on the power needed to throw the turnout and the supply voltage. The value of the charging resistors depends on how quickly the turnout will be returned to its last position. A resistance of 1000 ohms would be a practical value in most cases.
The resistors should have a 1/2 watt or greater power rating. The capacitors should have a 35 volt or higher rating.
NOTE: Most of the circuits are shown with DPDT toggle switches but 3 and 4 pole switches could also be used with the extra poles controlling frog polarity or LEDs.
For more information on other Capacitor Discharge - switch machine power supplies, follow this link. Capacitor Discharge - switch machine power supplies
The first three circuits are for use with switch machines that have and unbreakable connection between the two coils such as those made by Atlas®.
In the first circuit the LED that is lit will turn off slowly when the turnout is thrown to the opposite side.
In the next two circuits the LED that is lit will turn off quickly when the turnout is thrown to the opposite side. The circuits are accordingly more complex.
All of the following circuits are designed so that the indicator LEDs have "Fast Turn Off". These circuits cannot be used with switch machines that have separate coils.
The next circuit uses darlington transistors in the high current portion of the circuit. This would allow low currents in the control panel wiring.
This circuit has fast LED turn off. The LEDs could also be supplied from a separate power source.
The next circuit is very basic with or without indicator LED's. Due to the low value of R1 (220 to 100 ohms) the power supply would have to be more robust than if 1000 ohm resistors were used.
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.
19 June, 2009