1. Impact Printers
How they work

2. Impact Printers Physically Hit The
Paper
• Impact printers are one of the earliest types of hard copy
output devices used with computers. These printers, so
named because of the physical impact they make with
the printing surface, function by physically striking the
surface to be printed, much like a traditional typewriter
would do. The three primary types of impact printers are:
dot matrix printers, which print one character at a time
using an adjustable-pin print head; daisy wheel printers,
which rotate a wheel containing every printable
character to the appropriate position before striking the
paper; and line printers, which print an entire line of text-
-rather than a single character--at a time.

3. Impact Printers Use Magnets
• To facilitate the high-speed impacts necessary to
generate an impact print, printers use a small
form of electromagnet to operate their movable
print heads. Impact printers feature either a
combination of pins that can move toward the
print surface or, as is the case with a daisy wheel
printer, a wheel that can spin to access the
desired character. Dot matrix and line printers
work with similar technology; when the printer
receives data, a logic board on the printer
interprets the data and generates a series of
electrical impulses.

4. – These impulses travel to the print head, where an
electromagnet converts them to physical movement
of a print head; the print head moves a series of pins--
ranging from 9 to 24 on a dot matrix printer and 9 to
24 pins per character on a line printer--toward the
paper. Each of the pins creates a small dot on the
paper that, when combined with the other dots
generated by the print head, forms the shape of a
letter. Daisy wheel printers use similar technology, but
use the electromagnets to first spin a wheel to the
appropriate printable character before sending the
character toward the print surface.

5. Impact Printers Use Ribbon
• Except in the case of sensitive carbon paper, the impact
of a printer's pins are rarely sufficient to generate
permanent, readable text on a printing surface. To
augment the printing process and leave a more readily
apparent mark on the paper, impact printers insert an
ink-covered ribbon between the print head and the
paper. When the print head touches the paper, the
impact transfers a small amount of ink from the ribbon to
the paper. This process helps ensure the document
produced is readable for some time to come, though the
ribbon itself is prone to being used up (especially in high-
volume printing environments).

7. Barcode Scanners
•How they work

8. How do Barcode Scanners work?
• To understand how a barcode scanner works, we have to explore the
different parts of the device. Basically, there are 3 functional parts to the
barcode scanner itself, the illumination system, the sensor /
converter, and the decoder.
• The simple explanation...
• Barcode scanners begin by illuminating the code with red light. The sensor
of the barcode scanner detects the reflected light from the illumination
system and generates an analog signal with varying voltage that represent
the intensity (or lack of intensity) of the reflection. The converter changes
the analog signal to a digital signal which is fed to the decoder. The
decoder interprets the digital signal, does that math required to confirm
and validate that the barcode is decipherable, converts it into ASCII
text, formats the text and sends it to the computer the scanner is attached
to.
• Let's look at each functional part of a barcode scanner in more detail:

10. Single Point LED
• - This technology is exclusive to the barcode wand
reader and the barcode slot reader. The illumination of
the barcode comes from either a single or pair of LED's
and is focused through a single ball-type opening. This
technology requires the ball to physically touch the
barcode being scanned.
• Since the illumination is on a single point, the operator
has to provide motion to the barcode past the light
source. In the case of a barcode wand, the operator
drags the illumination ball across the barcode. For
swipe or slot readers, the barcode is typically printed
on a credit-card like media. The operator pulls the card
through a fixed slot, past the illuminating head.

11. • Slot and wand readers are inexpensive, and can
accommodate any length of barcode. There are several
disadvantages of the single point illumination method.
Slot and wand readers require the operator to control
the speed at which the barcode passes in front of the
illumination head. Because barcodes must be in
contact with the illumination head to read, the barcode
can easily be damaged by abrasion of the head on the
media that hosts the printed barcode. Although the
illumination head is hardened, it will wear out and
must be replaced regularly.

12. Linear Multiple LED
• Expanding on the single-point illumination system,
placing multiple LED's in a line give the ability to light
the entire width of the barcode. This type of
illumination is used in CCD scanners and Linear
Imagers.
• When used in CCD scanners, the LED's are paired with
a line of photocells to detect the reflected light from
the barcode Since the LED's are relatively low in
power, and the photocells are low in sensitivity, the
range of CCD barcode scanners is generally limited
from being in contact with the barcode to 1" away

13. Laser
• - This type of illumination method uses a single point
red laser diode similar to a laser pointer. The point of
light is expanded into a line by oscillating the laser into
a stationary mirror, or projecting the point into an
oscillating mirror. This illumination method is very
popular because of the working distances typically
achieved are superior to the point illumination or
linear LED illumination methods. Typical working
distances are from 1" to 18". By increasing the power
of the laser and decreasing the angle of oscillation,
ranges of over 20 feet can be obtained.