Chapter 8 Control Heads
Model I
Introduction
The Control Head forms the interface between the radio and the user. It contains an LCD display, on/
off and volume switch, keypad and control keys.
The microprocessor controlled Control Head interfaces to the radio control logic board J0650 via an
18-pin connector on the back of the unit. An external microphone/speaker is connected to the
Control Head via the front mounted microphone connector P0651.
Power supplies
Power supply A+ (pin 17) is routed directly from the radio through the 18-pin connector and is used
for LCD and keypad backlight LEDs and indicator LEDs.
Power supply B+ (pin 18) is routed from the radio battery via the radio on/off switch and provides Vcc
via regulator U0654.
Option SW B+ (pin 1) is the power supply output to the connected accessory. The current is
monitored by the Control Head to operate the multiplexer. (Refer to Mode Select)
Audio configuration
The Control Head can be configured for Handset audio or Speaker+ which is a balanced output from
the radio. Handset audio is configured by inserting R0676 in the line from pin 8 to the microphone
connector. Speaker + audio is configured by inserting R0675 in the line from pin 1 to the microphone
connector. Note that only one resistor R0676 or R0675 must be fitted.
Volume Control / on-off
Front panel switch/potentiometer R0698 controls the volume via A/D converter PD0 (pin 14) in
micro-controller (µC) U0653. The centre of the potentiometer is a push button switch used for
microphone input and power on-off. When activated the microphone line (pin 9) is connected to
ground.
Micro-controller
Micro-controller U0653 controls the operation of the Control Head. The µC exchanges data with the
radio via the SB9600 bus (TD0 and RD1) and monitors inputs from the microphone connector via the
A/D port (PD0-PD7). The µC is reset from the radio via the reset line (pin 3) and Q0652.The µC is
also reset by under voltage detector U0657 when Vcc drops below 4.6V.
Xtal Oscillator
The xtal oscillator is built using on chip oscillator gates of the microprocessor. The xtal is a standard
4 MHz ceramic resonator.
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