doorchime driver

The bell-wiring-system in many blocks of flats consists of a set of pushes in the communal entrance hallway, a centrally-located (and inaccessible) transformer and a cheap-and-nasty trembler bell in each flat. One`s own front door is then usually fitted with a kind of king-size bicycle-bell that requires considerable force to be applied to the push. Since the whole set-up is a minimum-price job, the avail- able current is invariably too low to operate a full-length door- chime, particularly when the flat concerned is located on a higher floor. It is also not normally possible to connect a bell-push on the flat-door into the system. The circuit described here is the result of one engineer`s taking up the gauntlet ...