Shure U1/U1L Body-Pack UHF Transmitter
25C1021 (BG)
4
Circuit Description
Transmitter Display Board
The display board consists of the following circuitry blocks.
Microcontroller Section
The microcontroller section consists of microcontroller U103 and the
liquid crystal display (LCD). The microcontroller has an on-board liquid
crystal display (LCD) driver. R111, R113, and R114 supply the microcon-
troller with the LCD drive voltage for a four-plex drive. The LCD indicates
the UHF frequency group and channel. The LCD also has a battery fuel
gauge. A 4.000 MHz oscillator, Y101, provides the operating frequency to
the microcontroller. The oscillator circuit includes C107, C108, R102, and
R103, which along with Y101, U106, R112, and C112, form the reset cir-
cuit. U106 is the reset integrated circuit (IC) that resets the U103 micro-
controller if the 5 V normal operating voltage falls below 3.5 V. R107 is
the pull-up resistor for the U103 programming voltage pin.
Memory Section
The memory section consists of U101, a non-volatile EEPRAM,
that stores current transmitter settings and the mapping of compatible
groups and channels.
Battery Management Section
The battery management section consists of comparator U102. It is
used to measure the effective battery voltage, with reference to +5 V, by
measuring the time used to charge a capacitor to a reference threshold
of 0.1 Vdc
±
0.01 Vdc. The battery is checked approximately every 5
seconds. Comparator U102 alternately charges C106 with +5 V refer-
ence voltage, then the battery voltage (PLUS signal, test point I109).
User Interface Section
The user interface section consists of the Power, Mode, and Set
switches. The status of each switch function is indicated on the LCD.
Power Supply Section
The U105 dc-to-dc converter provides the transmitter with regulated
+5 V derived from two AA batteries. Power MOSFET Q101 provides
reverse battery protection. Q103, R118, R286, and C124 control the
soft start and reset of dc-to-dc converter following battery voltage drops.
