These circuits are to designed to convert the inputs from 2 SPST swiches and convert it to 4 discrete outputs. Depending on the particular circuit used, only one output can be HIGH or LOW at a time.
The NAND and AND logic gates can operate in either the HIGH or LOW output mode as their outputs are bipolar. The output of the logic devices could also be the open collector type.
The number of SPST inputs and discrete outputs can be increased by using additional logic gates with an input for each set of contacts.
This circuit is designed to take its input from the switched contacts of two Tortoise® type switch machines that operate a double-slip turnout and covert these to 4 discrete outputs that control 4 sets of 3 aspect signals.
One aspect on each signal will show on each signal head depending on how the turnout is set.
Because there are four slip switch settings but only three LEDs per signal, one of the aspects on each signal is used twice. In this example the Red LED is used twice for each signal but the other colours could be use twice as well.
For a crossover made with two turnouts the signals could be wired so that: Red shows for the blocked route, Green shows for the through route and Greeen/Yellow shows for a diverging route.
It is possible to control the the adapter circuit directly from DPDT toggle switches or 556 switch machine driver outputs that operate the switch machine's motors. This would allow both sets of contacts on the machines to be used for frog power.
The next diagram can be used to sort out the aspect logic of the system befor adding the electronics.
The circuit simulates the output of the 2 Sets Of 2 Inputs To 4 Discrete Outputs adapter circuit using four SPST switches. Only one of the SPST switches can be closed at a time.
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.
21 February, 2012