
Audio Output
BZ1, a piezo ceramic sounder, is the audio output device. Due to its low drive current of 2 mA maximum, no
drive circuitry is needed and is driven directly from the external output port. It is differentially driven with 2
square waves 180 degrees out of phase. The drive frequency is approximately 1480 Hz or 740 Hz and is
generated by the CPU. BZ1 is differentially driven to obtain maximum audible volume.
Display Control Circuitry
The Taliq display is controlled by the display control circuitry. A photosensor measures ambient light and
automatically switches on the electroluminescent display backlight during low light conditions. The display
control circuitry is divided into the following subsections.
•
Control Conditioning Circuit (main PCB) – The control conditioning circuit processes signals generated by
the CPU to produce timing signals for the display drivers.
•
Display Driver ICs (auxiliary PCB) – Each of the two display driver ICs have 32 high-voltage outputs that
enable individual segments of the display to be turned on or off.
•
High Voltage Control Circuit (auxiliary PCB) – The high voltage control circuit allows the CPU to switch on
or off the display's high voltage input.
12-17
Microprocessor
Main PCB
Control
Conditioning
Circuit
(generates
timing
signals)
Main PCB
Display
Display Driver
(1)
AUX PCB
Display Driver
(2)
High Voltage
Control Circuit
(enables
+70 VDC
to display)
AUX PCB
Display
Backlight
70 volts
Figure 12.5 Display Control Block Diagram