鈥?HBCC-1570 - 0.013 in.
- HBCC-1580 - 0.007 in.
- HBCC-1590 - 0.005 in.
output of different sensor 鈥渂ins鈥?/div>
is equalized by varying the
amplitude of the LED drive
current.
The sensor output has two com-
ponents; DC due to ambient light,
and AC from the bar code label.
Photocurrent from the sensor is
amplified and high pass filtered
to remove the ambient light
signal. The AC component is
amplified and sent to an AM
detector to recover the bar code
information. The recovered bar
code signal is low pass filtered to
eliminate the 30 kHz carrier. The
signal is input to a digitizer
consisting of positive and negative
Description
The Hewlett-Packard Low Current
Bar Code Digitizer IC allows
designers to incorporate the high
ambient light rejection and low
power consumption features of
the HBCS-AXXX/TXXX wands
into their own bar code circuitry.
The HBCC-0500 is packaged in a
24 pin SOIC plastic package.
peak detectors and a comparator.
The comparator threshold is
generated from the peak
detectors using a resistor ladder.
This threshold, along with the
current bar code signal, is input
to a comparator. The output of
the comparator drives an external
output transistor.
Block Diagram
SENSOR
LED DRIVER
Theory of Operation
The digitizer IC uses the tech-
niques in US Patent 4,682,015 to
reduce power consumption and
sensitivity to ambient light.
Power is reduced by pulsing the
LED every 33 microseconds with
a 1 microsecond pulse. The
AMPLIFIER
HIGH PASS
FILTER
AMPLIFIER
AM
DETECTOR
LOW PASS
FILTER
DIGITIZER
OUTPUT
5964-1563E
4-33
1
2
3
4
