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Model 2241-3 & 3i
Technical Manual
Section 7
Ludlum Measurements, Inc.
Page 7-3
January 2016
S2-S4
S2-S4 are pushbutton switches which enter/change the variables for each of
the 16 parameters.
U1
U1 is a +5 V powered RS-232 driver/receiver used to interface the Model
2241-3 to a computer.
LCD Drive
U111 and U211 are serial input 32-bit LCD drivers. The data is loaded
serially into the 32-bit shift registers (internal) via the “D” IN input. The
LOAD
input instructs the shift register to receive data while the
CLOCK
input
shifts the data through the 32-bit registers. After all the data is loaded, the
LOAD
line is pulsed by the µP, instructing the registers to transfer the data to
the LCD drivers. The backplane (BP) signal from U211 provides the
reference signal (approximately 125 Hz at 5 Vdc) to the LCD (DSP1) BP
connection. When a segment is illuminated, the signal to that segment will
be out-of-phase with the BP signal. If the segment is
OFF
, the signal will be
in-phase with the BP signal.
Backlight Drive
Depressing the
LIGHT
button instructs the µP to set the
BACKLIGHT
line, pin
31 on µP, "low" for the predetermined backlight
ON
time. (Refer to main
board schematic for details.) A "low" condition on pin 31 causes Q212 to
conduct s3 V to P8-3 on the display board with +3 V at P8-3
(refer to display board schematic). Backlight oscillator Q011, T011, and
related components start to oscillate, producing a 2.5 kHz, sine wave signal.
The signal is amplified by T011 to 150 volts peak-to-peak to drive the LCD
backlight.
Refer to Display
Board schematic
for the following:
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