The Programmable Logic Controller (PLC) is a light-weight, low-cost and self-contained solution for a wide range of residential applications. Today’s homes are incorporating more electrical appliances and systems, which in turn require more controls. The PLC’s ladder logic implementation allows greater flexibility of control, since all the hard wiring between points of control is done electronically.

Presently, lighting control is done with toggle switches which turn the power on or off to the lights. Depending on the quantity of lights in the home, there will be a number of toggle switches located throughout the house. Some rooms could have up to four toggle switches on the wall.

Using the PLC as the lighting control eliminates the toggle switch wall clutter, by replacing it with a low voltage switching solution. The low voltage keypad is a momentary contact device with multiple buttons.

The keypad is strategically located in the home, so as to allow for lighting control of the total room or the entire floor.

The keypad is wired back to the PLC’s input unit located near the power distribution panel.

The PLC’s output unit is wired to all the lighting loads via the power distribution panel. Once all the lighting circuits are wired directly to the input/output units built into the PLC, the actual control is programmed in the ladder logic.

The application program for a typical lighting control is shown below;

The keypad switch (10001) is programmed as a positive transitional contact which passes power for only one scan as the input transitions from OFF to ON. Depending on the status of the light, on or off, the keypad’s On State or Off State will be determined with coils (00101) and (00201). If the light is on, the keypad switch will turn the light off. If the light is off, the keypad switch will turn the light on. The coil (00001) is the lighting circuit output, which is wired to the lighting load via the power distribution panel.