57
Basic circuit diagram of door entry system insta-
llation with speech privacy, for use in buildings with
two entrances.
Alcad multiple entrance systems are based on the
use of microprocessor-controlled audio units (micro-
processor-based 4+N system). Rather than using
changeover switches to select one of the entrance
panels, the audio unit has been fitted with a micro-
processor that decides which entrance panel should
be activated, and disables the rest of the panels in
the system.
This system simplifies the cabling of the installa-
tion, reduces the number of components and impro-
ves system operation.
Telephones with the privacy of conversation featu-
re remain inactive until they are called from the
entrance panel. Until a call is received the dwelling
telephone is disabled so that it is not possible to lis-
ten to conversations between other tele-phones and
the entrance panel.
Operation
One of the entrance panels in the system is chosen
to be the main panel just one panel per installation
can be defined as the main one. To select it, remove
jumper J1 from the other entrance panel. The main
panel is the one which is connected by default to the
system’s telephones. The other panel is only activa-
ted when one of the call buttons is pressed.
When a call button is pressed, the corresponding
panel is activated to allow communication with the
telephones. The system busy indicator light on other
panel will start to flash to indicate that it is disabled.
When one of the push buttons on one of the
entrance panels is pressed the electronic call signal
generated by the audio unit (7) is sent via the call
line to the corresponding telephone (5), where it is
heard on the loudspeaker of the handset. At the
same time the audio unit’s own loudspeaker gene-
rates a sound to confirm to the visitor that the call has
been made. The audio unit also generates a control
signal (17) that disables the other entrance panel.
The telephone that receives the call is activated by
connecting its electronics internally to the common
wire (2) and the door lock wire (1). While the tele-
phone is activated on it is possible to open the door
or communicate with the caller by picking up the
handset. Once the call is received, the audio unit
starts a 30 second timer while it waits for the tele-
phone handset to be picked up. If the handset is not
picked up during this time, the control signal (17) is
removed and both panels go into the standby state.
If the handset is picked up during this time, the
electronics associated the telephone’s audio lines (3
and 4) is internally connected to the entrance panel.
This connection sets up the communication between
the telephone and the entrance panel. The audio
unit starts a fresh 60 second period before disabling
the telephone and removing the control signal (17),
putting both panels into standby state. When only
10 seconds are left a buzz will be heard. It is possi-
ble to restart the timer either from the entrance
panel, by pressing the push button, or from the dwe-
lling end, by pressing and releasing the telephone
handset’s hook switch. After finishing the communi-
cation, when the audio unit detects that the telepho-
ne handset has been hung up, it removes the control
signal (17) and both panels go into the standby
state.
When the door lock release button on the tele-
phone is pressed, the audio unit detects the closing
of the lock release circuit (1). The audio unit then
sends an a/c voltage (11 and 12) to the electric lock
connected to the active entrance panel, thus allo-
wing the entrance door to be opened.
The common wire (2) of the telephone and entran-
ce panel provides the return path for all the telepho-
ne signals. The common wire is connected while the
telephone is active.
TWO ENTRANCE INSTALLATION WITH ELECTRONIC CALL
AND PRIVACY OF CONVERSATION
MICROPROCESSOR-BASED 4+N SYSTEM
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