Hand Held Products IT4000, Руководство по интеграции

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IMAGETEAM™ 4X00 Series Integration Manual 2 - 11
Concurrent Mode
Concurrent Mode may be implemented to provide a more intuitive method of aiming if you are using linear bar codes. The aiming
LEDs/Laser and illumination LEDs are turned on simultaneously. The aimer remains on for the duration of the scanning/decoding
session.
Concurrent Mode is controlled using the Illumination On and Aimer On control signals. Driving both control line active high at the
same time causes the aiming and illumination to turn on at the same time at full intensity.
Note: The intensity can be adjusted using the LED Power Control PWM (see page 2-11).
The image engine draws more power when in Concurrent Mode than when in Interleaved Mode. Refer to electrical
characteristics for current draw information for the different modes.
Laser Aimer Thermal Considerations
The laser aimer dissipates a significant amount of power as heat. The illumination LEDs also release heat and are a major
contributor to thermal increases in high use or in presentation mode.
An increase in temperature around a IT4300 Series engine can cause noise levels on the imager, degrading image quality. The
thermal rise can also affect the laser diode. In a continuous scanning or high use environment, the IT4300 Series engine
temperature can rise 15° to 20° C. Under high ambient temperature conditions, the laser diode is at risk of thermal breakdown
and possible failure. The image quality and decode performance will also degrade.
The Power Control PWM can be used to reduce the effect of the illumination LEDs on thermal rise, however, this also reduces
the intensity of the illumination. Reducing the intensity of the illumination reduces total power used but can also reduce the depth
of field.
LED Power Control PWM
Note: LED PWM has no effect on laser aimer power.
The LED Power Control PWM allows the system to control the current drawn by the LEDs. The host system can drive this line
with a 7.5KHz pulse width modulated waveform to control the current regulation of the LED power supply.
Reducing the current/power also reduces the intensity of the illumination. This reduction in light levels directly impacts the
reading attributes of the image module. A reduction in light levels reduces reading distance to target and depth of field
performance.
Duty Cycle Current Draw Relationships
LED Current for Selected Duty Cycle Settings
The LED current per duty cycle setting exhibits a near linear response to a DC of 70%.
The following table provides a list of the typical current values provided to the LEDs for specific duty cycle (percent current)
settings.
Percent Current (%) Duty Cycle (%) Approximate LED Current (mA)
100 0 40
95 5 38
90 10 36
85 15 34
80 20 31
LED Power
Control
50% Current 100% Current 90% Current 10% Current