Shure U2 Hand-Held UHF Transmitter
Circuit Description 25B1022 (AG)4
operating frequency to the microcontroller. The oscillator circuit includes
C102, C103, R106. R108. U105, R113, and C107 form the reset circuit.
U105 is the reset IC that resets U104 microcontroller if the 5 Vdc normal
operating voltage falls below 3.5 Vdc. R112 is the pull-up resistor for the
U104 programming voltage pin.
Memory Section
The memory section consists of U101, a non–volatile EEPRAM chip
that stores current transmitter settings and has the mapping of the com-
patible groups and channels.
Battery Management Section
The battery management section consists of comparator U103. It is
used to measure the effective battery voltage, with reference to +5 Vdc,
by measuring the time taken to charge capacitor C105 to a reference
threshold of 0.1 VDE ± 0.01 Vdc. The battery is checked approximately
every five seconds. Comparator U103 alternately charges C105 with +5
Vdc reference and then the battery voltage (DPLUS signal). The micro-
controller calculates the battery voltage by comparing the time difference
to charge C105, up to a reference threshold of 0.1 Vdc ± 0.01 Vdc, with
the +5 Vdc reference voltage and the battery voltage.
User Interface Section
The user interface section consists of power, MODE, and SET
switches. The LCD provides the user with feedback for all switch
operations.
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