Shure U4D Dual Diversity UHF Receiver
5 25D1062 (AG)Circuit Description
the LEDs. The output from this stage drives the audio level meter on the
front panel board.
A dc voltage from the detector chip RSSI drives the bar graph
integrated circuit on the front board for the rf level meters.
Display Board / Digital Section
Microcontroller Section
The microcontroller section consists of microcontroller U103 and the
liquid crystal display (LCD). The microcontroller has an on-board LCD
driver. R104, R116, and R118 supply the microcontroller with LCD drive
voltage for a four-plex drive. The LCD is a transmissive type that uses a
backlight for optimum readability. J104 supplies current, limited through
5 Ω (paralleled R119 and R120), +5V for the LCD diffused backlight LED
array.
The LCD indicates frequency in MHz, a user-programmable name
up to 8 characters long, and the UHF frequency group, channel, and
television channel.
The LCD also has a battery fuel gauge that indicates the state of
the transmitter battery. A padlock icon on indicates whether the user-
accessible menus are locked or unlocked. A 4.000 MHz oscillator (Y101)
provides the operating frequency to the microcontroller.
The oscillator circuit includes C107, C108, R111, R112, and Y101.
R105 and C103 form the reset circuit. R121 is the pull-up resistor for the
U103 programming voltage pin.
Memory Section
The memory consists of non-volatile ferroelectric RAM or EEPROM
U106, which stores current receiver settings and maps of compatible
groups and channels. R108 and R109 allow in-circuit programming of
U106 FRAM.
Analog to Digital Converter Section
The analog to digital converter section consists of A/D converter
U101. Signal DLOW_BATT (P102.2, U101.2, I138) from the audio sec-
tion is an analog signal representing the transmitter’s battery level. This
is converted to an 8-bit digital signal for the microcontroller and is dis-
played on the LCD as the battery fuel gauge. Microcontroller U103
communicates serially with A/D converter U101.
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