BARRETT 900 SERIES TRANSCEIVERS
The Front Panel PCB allows user control of the transceiver. An integral rubber keypad provides functional
control. The LCD display presents channel, frequency and status information and the five status LED's
indicate mode and Tx / Rx state. Backlighting for the LCD and keys is provided and a volume control varies
the audio level from the loudspeaker. A microphone socket allows the use of a three button microphone,
providing PTT and channel Up/Down functions. Note:- The standard microphone has a jumper in it (refer to
the microphone diagrams) that enables the front panel speaker, the handset does not have this jumper thus
disabling the speaker.
Data to refresh the front panel LCD is sent from the microprocessor PCB, via the Audio / IF PCB on one serial
data line. This serial data is processed on the front panel by embedded microprocessor U1, and converted to
parallel data for use by the LCD and mode and operational state status display LED's. Q8 provides buffering
of the serial data line from the main body of the transceiver.
Data from the 20 function keypad matrix is PWM encoded by the keyboard encoder U2. This is buffered by
Q9, and sent via the control cable and the RF/Audio PCB to the microprocessor PCB. The microphone
channel up and down buttons are also handled by U2. Channel up and channel down functions come from
the microphone socket pins 3 and 2 respectively.
Backlighting for the keys is provided by parallel LED's D6-D12 which are in series with the LCD display's
internal backlight diodes. Port RB7 and RB6 are used to provide intensity control of the LCD via Q1.
Extended temperature range on the LCD display is achieved by controlling the polarising voltage on pin 3
using a thermistor TH1.
The microphone socket has EMC filters to prevent pick up of RF by the balanced microphone leads. Two
lines allow the channel up/down key function on the microphone as described above.
The volume control VR1 provides a voltage that controls the voltage controlled amplifier located on the
RF/Audio PCB The lower the voltage output from VR1's wiper the higher the volume. The On / Off switch
provides a ground to the main body of the transceiver to switch the transceiver on. This ground is also used
to apply the 13.8 VDC to the front panel, this in turn switching on the +5V DC supply for the front panel logic.
4.4 Front panel
4.4.1 LCD and status LED's
4.4.2 Keypad
4.4.3 Backlighting
4.4.4 Microphone
4.4.5 Volume control and On/Off switch
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