Model VR240 Audio Logging Recorder
4-8
January 2000
Section III. VR240 THEORY OF OPERATION
4-14. MAIN
COMPONENTS.
The main components of the VR240 are:
Input Boards (signal conditioning, A/.D and D/A conversion, data reduction)
CPU Board (microprocessor, memory, SCSI, clock, Ethernet, communication ports)
Removable-media Drives (tape, MO disk, DVD-RAM)
Internal fixed hard disk drive
Motherboard (backplane for CPU and Input boards, audio mixer)
I/O Control Board (audio output and display control circuits)
Front Panel Assembly (keyboard, display, status indicators)
Switching Power Supply
Uninterruptible Power Supply with Battery Charger
4-15. GENERAL
OPERATION.
NOTE
The following description assumes that standard telephone input
boards are installed. See Figure 4-1.
Signals to be recorded are connected to the input boards. The front-end circuits condition the
signals according to user settings for gain and AGC. The conditioned signals are filtered and
converted from analog to digital. The digitized signals are pass through a data reduction
algorithm (standard G.726 ADPCM), resulting in a data rate per channel of 64, 32, or 16 kilobits
per second. Data from all channels is transferred from the input boards to memory on the
CPU3 board. A decision is then made for each channel whether to save the data or ignore it,
depending on the user setting for channel activity (OFF-HOOK, VOX, etc.). Data for active
channels is transferred from memory to the fixed hard disk drive. After a certain amount of data
is accumulated on the disk drive, it is then transferred from the hard disk to memory and then to
the removable media. If the removable media is full or not loaded, data continues to
accumulate on the hard disk. All data is time coded so as user can easily locate desired
material by searching for a time and date.
Playback is the reverse of recording. Once the desired data is located (either on the hard disk
or on a removable-media drive that is not in record mode), the data is transferred to memory
and then to the input boards for playback. The data is converted to analog, and the signals from
all enabled channels are mixed to a single channel and played through the speaker (or
headphones) and the line-out jack.
The CPU board features a Motorola 68000-family microprocessor running a proprietary real-
time multitasking operating system. System firmware is stored in Flash ROM and can be
updated in the field. Updates are created periodically to add new features and to support
different types of SCSI removable-media drives (such as the new DVD-RAM drives).