DRM 85-C, DRM 85
09/2007
7/41
3
Description
3.1
Mechanical design
Mechanically DRM 85 is based on the Sennheiser Evolution Wireless (generation 2)
handheld microphones. A new rear cup was designed to accommodate the
keyboard with the push buttons and make accessible a red LED, the user interfaces
like USB, headphone output and the rotary control switch.Due to EMC and ESD
requirements the rear cup in the same material as ew-G2 has got a metallized coat
underneath the lacquered coat.
3.2
Electrical design
DRM 85/ DRM 85-C contains four printed circuit boards:
•
AF Board
•
Connector Board
•
CPU Board
•
Keyboard
The KE10 capsule is optimized to an omnidirectional characteristic specially for
DRM 85 as well as KE14 to a cardioid characteristic for DRM 85-C. The signal of the
capsule is preamplified, digitized and linked via the connector board to the
coldfire processor on the CPU Board.
The AF board contains the preamplifier, the preemphasis, the codec and a
headphone amplifier for monitoring the recorded or the playback signals. The codec
has an onboard A/D-and D/A converter.
The connector board contains the user interfaces like headphone output jack, USB
jack and the LC display. It links all control and data signals to and from the codec
on the AF Board to the processor on the CPU Board.
The CPU Board contains the power supply section, the CPU section with the coldfire
processor for controlling and signal processing and the memory section with the
code flash, the SDRAM as a working memory and the data NAND flash.
The keyboard contains the three buttons: Record, Play, Menu/ Stop.
3.3
Functional description
3.3.1 DC supply
Starting with the power supply section located on the CPU board, the system
obtains it´s power from a pair of AA type batteries, which can be either primary or
secondary cells thus producing a total voltage of 3.0 V in the case of primary cells
and of 2.4 V in the case of secondary cells.
If a special Sennheiser accu-pack is used, it can be identified by no voltage at the
layer pad M3. In all other cases there can be measured U_accu/2 at M3.
The battery voltage needs to be converted to the system voltages 3.3 V and the
processor core operating voltage 1.8 V , from which the device operates. For this
purpose a small switching converter is used principally comprising of U600, L600
and D602. This circuit produces a constant 3.3 V at the main reservoir capacitor
C611.