BWT Bewamat 20 integration

I have an about 30 years old water softening system: Bewamat BWT 20. It has a 7-segment-display, which counts the water and displays SALZ, if the salt needs to be refilled. Does anybody know, if it is possible to integrate this water softener e.g. with an ESP8266 to get a notification, when salt needs to be refilled? Probably there is a pin or anything which can be used with an ESP8266 to read the status.