Theory Of Operation - Symbol SE 2223 Integration Manual

SE 2223/3223 Scan Engine Integration Guide
A flex cable connector mounted on the SE 2223/3223 provides connection between the
scanner and host. The SE 2223 and SE 3223 use the same hardware and software
components, but differ from each other in the following ways:
• The SE 2223 employs focusing more suited to reading 1-D and PDF symbols using
a raster laser pattern. The working range is larger than the SE 3223.
• The SE 3223 uses focusing more suited to reading 1-D bar codes in an
omnidirectional manner while still able to decode PDF symbols in a raster mode.

Theory of Operation

The scan pattern is created via a laser diode that produces a single beam of coherent light.
Two orthogonal scanning elements are contained within the chassis of the SE 2223/3223.
The laser light first hits the Y scan element mirror that can move the beam in a vertical
direction. The light beam is reflected to the mirror of the X scan element. By controlling the
scan angle and scan frequencies, the movement of the X and Y scan element mirrors
creates the various scan patterns.
When the laser light strikes a bar code, the dark bars absorb the light, and the light spaces
reflect it. The reflected laser light is bounced back to the scan engine where it reflects off
the X element mirror to the Y element mirror, then to the collection mirror. The collection
mirror focuses the light onto a photo diode which generates a current proportional to the
reflected light signal. That current, in turn, produces an analog voltage which is amplified,
filtered, and sent to a digitizer. Here the signal is transformed into a digital representation
of the bar code called the Digitized Bar Pattern (DBP). The DBP data is then sent to the
decoder board for processing into the SSI format.
The heart of the SE 2223/3223 is a custom Application-Specific Integrated Circuit (ASIC)
and a single chip decoding system (SCDS), which control the majority of functions
associated with a laser-based scanner. The ASIC controls the analog front end, the
digitizer, the Visible Laser Diode (VLD) driver, and control circuitry. The VLD driver circuit
turns the laser on and off, and regulates power to the laser. It incorporates a motor fail
detection circuit that turns the laser off should the motor fail.
The SCDS controls the X and Y scan element mirror motion, which oscillates the X and Y
mirrors at the required frequencies in order to produce the various scan patterns.
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