Symbol SE 923, Integration Manual

Page: 18 / 238

1-2
SE-923 Scan Engine Integration Guide
All SE-923 interface signals are TTL compatible. In order to communicate with an RS-232
device, RS-232 drivers are required.
Laser Scan Engine
A laser diode produces a single beam of coherent light which deflects off a mirror, and is
emitted from the SE-923. The mirror is attached to a resonant scan motor which oscillates at
19.5 Hz nominally. The total deflection of the single beam is 53° (standard version), and the
scan frequency is 39 scans per second.
When the light strikes a bar code, the dark bars absorb the light, and the light spaces reflect
it. A photo diode senses the reflected laser light and 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 a host-compatible format.
When the SCAN ENABLE and LASER ENABLE lines are brought low, the control circuitry
activates the laser and motor driver circuits, turning on both the laser and motor. The laser
driver circuit regulates power to the laser. The motor driver circuit controls the mylar
“motor” (resonant scan element).