Telephone Operated Car-Parking Remote-Control

I got a friend who works for small start-up in a rented office. His problem is that they have only a single remote control to operate the parking lot gate. They needed a device that will allow them to open the gate by using the cell phone.

I built a device that connects to a phone line and to a standard remote control. The device is actually a “docking station” for the remote control. When a ring is detected the device will “press” the gate-open button on the remote control.

This is how it's set-up in the office: and this is how it's used:

This is how the remote control looked like when I got it, before the modification:

I modified the remote control by adding a 2-pin port to the RC, one wire connected to each button terminal: The remote control ended up looking pretty nifty:

First thing I tested the circuit idea:

Then I built the actual circuit into its box. The box is a telephone line adapter box I got at ACE. Here is how the box looks from inside after construction: The circuit is actually a ring detector built using a W04 rectifier bridge, a voltage divider and a 4N25 optoelectronic coupler. The coupler transistor output is connected to a 555 in single-shot mode in order to give a reasonable pulse length to the button pressing. The 555 is connected to the remote control via the button port I described before.

I then tested it at home: