Shure UC1L Service Manual page 6

Shure UC1 Body-Pack UHF Transmitter
Battery Management Section
down threshold is 1.88 Vdc
threshold on pin 17 of the U101 microcontroller shuts down the transmit-
ter. Resistors R104 and R105 divide down the battery voltage for the
microcontroller. A battery voltage of less than 5.65 Vdc shuts down the
transmitter.
power output, and power downs the rf output amplifier section. The cur-
rent draw from a 9 Vdc battery in this state is 45 mA, and the battery fuel
gauge is functional. Turning off the power switch must completely shut
off the transmitter.
description.
Rotary Switches for Frequency Selection
S102, select the transmitter frequency. Both rotary switches share the
same U101 microcontroller port pins, 3 through 6, for a multiplexed
switch read operation.
switches. Resistors R109 through R112 are the pull-ups for the switch
position read. Diode packs D101 through D104 isolate the switches dur-
ing a multiplexed read operation.
detection based on interrupts. Also, the switches cannot be constantly
scanned to determine changes, because the scanning frequency being
in audio range is difficult to filter out.
U101 microcontroller pins 7 and 8. Pins 3 through 6 are outputs. In this
state, pins 4, 5, and 6 are held low, while pin 3 is held high. This forces a
logic high level on the switch selector pins if the switches are set on odd
positions. If the switches are set on even positions, the contact on pin 1
is open from the switch common pin, and the pull-down resistors, R114
and R115, force the logic low to pins 7 and 8 of U101.
vice versa. Only this change can be detected and is followed by a multi-
plexed switch read. In this case, U101 pins 7 and 8 become selectively
grounded outputs to read the selected switch's state on pins 3 through 6.
This mutes the audio in the receiver to allow a quiet change to another
frequency.
Characteristics
The microcontroller provides for low battery shutdown. The shut-
This auto shutdown disables the audio tone key mix, mutes the rf
The audio circuit description provided the battery fuel gauge circuit
A 10-position Group switch, S101, and a 16-position Channel switch,
Pins 7 and 8 of the U101 microcontroller select the individual
The multiplexed switch read system does not allow switch change
In a steady state, the switch selector common pins are inputs to the
Any switch change is made by a state toggle from odd to even, or
A multiplexed switch read is preceded by tone key and rf mutes.
6
10%. A voltage lower than the shutdown
25A1043 (RI)