The circuit uses a two coil, latching, DPDT relay as a form of memory to control a slow motion switch machine.
The the relay is triggered by a push button switch. The contacts in the switch machine selects which coil is operated by the push button.
Each time the push button is closed the relay will change states. This will reverse the polarity to the motor. As the motor travels, the internal contacts change which coil will be operated the next time the buttom is pushed.
Two version of the circuit are shown, they are the same except for the placement of S1.
If the push button is held closed the motor will change direction each time the switch machine's contacts change. The capacitor and resistor connected to the common connection of the relay's coil can prevent this.
This circuit uses a touch sensitive switch in place of the push button in the circuit above.
The touch input for this type of circuit is not ideal. Using current that is literally sourced from the air does not provide a steady flow. This could cause a noisy output creating unwanted turnout throws. To compensate, the circuit has Negative Recovery and Start Up pulse canceling.
This 555 timer will produce a continuously HIGH output as long as the input is active. Its output will go LOW about 1 second after the input is no longer active.
The next circuit uses a 556 timer configured as a D type Flip-Flop to provide the memory and drive the switch machine instead of a latching relay.
The next circuit uses a CD4016 Dual, D type Flip-Flop to provide the memory.
This circuit Is similar to the one above. It uses more ICs but fewer passive components. The 555A and 555B timers would be combined using a 556 timer IC.
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.
08 March, 2018