MagTek TRIPLE TRACK Delta ASIC - Manual (Page 16)

Triple Track ASIC
12
RECOMMENDATIONS AND PRECAUTIONS FOR MECHANICAL DESIGN
Most magnetic stripe reading devices on the market today, including this one, operate as temporal
decoding devices as opposed to spatial decoding devices. Temporal decoding describes the technique of
estimating the relative distances between flux reversals in the magnetic media by measuring the time that
has elapsed between the flux reversals passing the magnetic head gap during the swipe of a card. Spatial
decoding is a technique that allows for directly discerning the actual distances between flux reversals on
the card, but to apply this technique is relatively expensive. Temporal decoding relies on the assumption
that the acceleration from bit-cell to bit-cell as a card is swiped is insignificant in terms of distinguishing
one-bits from zero-bits. This applies to all temporal decoding devices.
It is critical for the mechanical designer to increase the probability that this assumption is valid. Thus for
a robust magnetic stripe reader there can be no sudden accelerations in the card path while the head gap is
in contact with the magnetic stripe. For hand-swipe readers here is a list of common problems related to
this concern that should be avoided while the magnetic media is in contact with the head:
1) Burrs or bumps in the card slot.
2) Smart-Card connectors contacting the card.
3) Card “gates” or latches that are actuated by the card motion.
4) Electro-mechanical switches that are actuated by the card motion.
5) Poor ergonomics that cause the hand to bump into an obstacle during the swipe.
6) Poor head spring design that allows the head to oscillate back and forth when a card is presented at
high speed.
For motorized card-drive devices, additional care must be taken. Here are some common additional
problems:
1) Stepper motor induced jitter.
2) Gear cogging induced jitter.
In addition to keeping the card motion smooth, the mechanical design must also minimize azimuth and
track location errors, allow for embossed cards, and keep the magnetic head in very close contact with the
magnetic stripe. Common problems related to these constraints include:
1) Head bounce causing poor head-to-stripe contact when the card is presented at high speeds.
2) Too wide a card slot, allowing the card to tilt beyond the compliance of the head spring, resulting
in poor head-to-stripe contact.
3) Too short a “lead-in” or poor swiping ergonomics causing azimuth errors for the typical user.
This is usually motivated by a desire to make the overall reader very small.
4) For insert-withdrawal or “dip” readers: azimuth error as the card is first inserted or right as it
leaves the slot in the case of withdrawal. Consider a deeper slot and/or a “floating” wear-plate that
allows the head to follow the azimuth error of the card as it enters/exits.