iI recently ran across this piece of surplus hardware from the late 90's/early 2000's. This is a Valcom model V-5324001 Door Phone Controller. Basically this device would be connected to an intercom box on a secure door and also to a phone system. When someone pushes the intercom button to gain entry it would ring a phone which could then be used to talk to the person at the door. This one has a date of 2002 on the bottom but some of the chips have date codes back into the 90s. The company that made it is Valcom which is still in existence. The company makes a range of communication products mainly focused a safety and security applications, and they still make a more modern version of this same device.
Under the flip up front cover are the limited external controls. The dip switches are used to setup the basic configuration of the unit, but the majority of the configuration is done from the telephone handset. The left knob controls the volume of the sound coming out of the door speaker and the right knob controls the volume of the sound coming back from the door microphone. Finally there is a LED that indicates the system status.
On the back are the connections to the system. On the left is an RJ11 jack used to connect to a phone system and next to it another RJ11 for connecting to a telephone handset. The system can work with just a handset of both a handset and phone system connection. On the right are all the external device connections. This would have had a screw terminal block that plugged into that socket but it was missing from the unit I found.
On the bottom is a label with all the typical regulatory information. There are also two patents listed which are quite relevant to this device:
In the manual there is a diagram of how the system can be used. When someone wants to enter they press a button on the intercom panel. This will ring that phone and optionally sound an alert through an external speaker which would be useful in a noisy environment. When the phone is answered it is connected to the door intercom so the person on the phone can talk to the person at the door. To permit entry the user would enter a code on the door which would unlatch the door. Alternately the system can be connected to a phone system. In this configuration the system can operate in two different ways. First, when someone pushes the door button a sound will be played through the Aux Alert Device and then the call can be answered from any phone by dialing the number of the PagePac. The other option is to configure the PagePac with a phone number that will be called when someone wants entry.
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On the left side is the power supply. The input to the supply is from an external 12VAC transformer. This 12 VAC goes through the bridge rectifier just below the transformer and then to the regulators at the bottom to produce +5VDC and +10VDC. The 12VAC also goes into the transformer and is stepped up to around 95VAC and then passed through two more bridges to produce two 24VDC outputs. I assume these higher voltages are for the phone circuitry since normal line voltage is 48VDC and ringer voltage can be up to 100 VAC.
Towards the lower middle is the analog phone circuitry, the small isolation is transformer is a prertty standard component of a phone line interface. The left three relays appear to be for controlling the phone line and the right relay appears to be connected to the door button inputs. Not sure why a relay would be needed for that. There are a couple un-populated components, a second connector, two relays and and support circuitry. The first empty relay spot goes to the un-populated connector and the second appears to go to the audio amplifier. I assume there was another model that had this additional hardware but I haven't been able to find any reference to it.
In the lower right corner is the audio amplifier probablty to drive the door speaker. This is built around a TDA1515BQ - 24 W BTL or 2 x 12 W stereo car radio power amplifier.
Finally, in the upper right is the digital control logic. The system is built around a Z0861108 microcontroller. This is a Z80 microprocessor with RAM, ROM and IO devices built into a single package. Most of the other chips around the processor are just general logic chips but there are a few interesting ones:
X24C44 - 256 Bit Serial Nonvolitile Static RAM. This is used to store the system configuration done through the phone keypad.
MT88700E - DTMF Decoder. This is a phone touch tone decoder which would be used to decode the keypad presses needed to configure the ssystem,
PCD3312C - DTMF Generator. This is a phone touch tone generator which would be used by the system to dial a phoner number.