ELM334

The ELM334 is a handy circuit for remotely monitoring the position of your garage door. A twowire interface is all that is needed to convey the position of the door to two remotely located LEDs, and to also provide control for an electric opener if desired.

This circuit continually monitors the state of two position sensing switches, representing the fully open and fully closed positions of the door. After suitable debouncing, the states of these switches are used to vary the polarity of the two signal wires, resulting in either the red (open) or green (closed) LED turning on. When the door is in neither position (moving), the LEDs rapidly alternate between the two colours.

If desired, circuitry to detect a short between the two LED wires can be added and used to operate a control output. If the door is equipped with a standard electric opener, this control signal can be used to operate the door. Refer to the Example Application section for further details.