The three circuits on this page can be used to indicate a trains direction of travel in a given section of track. The circuit does not rely on the track voltage so it can be used with any control system.
When a train covers one of the phototransitor sensors the circuit is triggered and the LED for that sensor turns ON. As long as the first sensor is covered the second sensor is disabled.
When the train leaves the sensor area the circuit reverts to normal until the next train arrives.
The sensors should be spaced about 1/4 to 1/2 of a carlength apart.
These circuits could be used at interlockings and diamonds to prevent a second train from entering the plant by cutting off the power to the track of the second train.
The first circuit does not have a recovery delay and could be affected by gaps between cars. The other circuits have a delay of about two seconds before the outputs switch off and can be retriggered.
The LM339 timer's output sink up to 15 miliamps.
The third circuit uses a LM556 timer IC as the output section and has a delay of about two and one half seconds before the outputs switch off and can be retriggered.
The LM556 timer's output can source or sink up to 200 miliamps and can have more accurate time delays.
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.
03 March, 2016