Gate control (again)

A few years ago I posted a topic about interfacing a GiBiDi gate controller to Indigo. There were no responses. I eventually kludged together a means of detecting gate open and closing events and that was that. However, I have now replaced my old controller with a new model (GiBiDi BA230) and have a possible new option.

There is a controller output that provides 24vdc according to the following pattern

Gate State - Voltage
Closed - 0vdc
Opening - 24vdc pulsed at 1Hz
Open - 24vdc (steady)
Closing - 24vdc pulsed at 2Hz

The gate takes around 20 seconds to open or close and I would like to detect the state as quickly as possible each time it changes. I can hook a relay up to the output so I can have dry contacts, or any control voltage I want.

Ideas?