Tait TM8100 mobiles Service Manual page 98

Power Supply
Volume Control
Main Keypad
LCD Module
Function Key LEDs
and Status LEDs
Keypad
Backlighting
Speaker
Microphone and
Concealed
Microphone
(Optional)
PTT
98 Circuit Descriptions
A 3.3V regulator (U1) converts the switched 13.8V supply from the radio
body to 3.3V. A 1.5V regulator (U203) converts the 3.3V to 1.5V.
A power-sense module (U202) verifies the outputs of the voltage regulators
and—in the case of a fault—creates a power reset signal which is processed
by the FPGA.
The voltage level of the volume control potentiometer is converted to a
digital signal by an analog/digital converter (U601), processed by the FPGA
and transmitted to the radio body.
The eight keys of the main keypad (function, scroll and selection keys) are
connected to the FPGA by an array of 3 columns and 3 rows. During idle
operation, the
KEY ROW
signals (pulled high by an external resistor) are monitored for activity by the
FPGA. A key-press will generate a high-to-low transition on the associated
column signal. This, in turn, will initiate a sequence of high output
KEY COL
levels on the signals to identify which key was pressed.
KEY ROW
The LCD module is connected to the control-head board via the LCD
connector. The LCD module display is controlled by a serial data link to the
FPGA. The backlighting and the optional heating element incorporated in
the LCD module are controlled by a data line each from the FPGA, which
switch two transistors on MOSFET Q102. A temperature signal from the
LCD module is converted to a digital signal by an analog/digital converter
(U601) and processed by the FPGA.
The function key LEDs (F1 and F4) and the red, green and amber status
LEDs each are controlled by an FPGA signal and a transistor (Q604 to
Q608). The brightness level is controlled by two FPGA signals, resulting in
four intensity levels (off, low, medium and high).
The keypad backlighting LEDs are controlled by two FPGA signals and two
transistors (Q2), resulting in four intensity levels (off, low, medium and
high). The keypad backlighting LEDs are arranged in two groups for the
main keypad and one group for the power button keypad, each group
consisting of three LEDs.
The two speaker lines (SPK+ and SPK–) are connected to the speaker
connector (J104) which is joined to the control-head connector (J103)
through two ferrite beads (L105 and L106).
The audio signals from the microphone connector or the soldering pads of
the optional concealed microphone are routed to a switching and pre-
amplifier circuit. If a dynamic microphone is required, the pre-amplifier is
engaged. The switching logic is used to select either the standard
microphone input or the concealed microphone signal. The dynamic
microphone must be activated in the programming software.
The PTT signal from the microphone connector is connected to the FPGA
via a resistor (R25) and relayed to the radio as a digital command.
signals are driven low by the FPGA and the
© Tait Electronics Limited November 2007
KEY COL
TM8100/TM8200 Service Manual