Hand swipe magnetic stripe encoder

Misaligned magnetic stripe cards are often improperly encoded during a write operation. The problem occurs most frequently in hand swipe encoders where the encoding operation may occur quickly without sufficient care to seat the card properly. A write - disable circuit responsive to the proper positioning of the card prevents such improper encoding, and destruction of valid encoding on adjacent tracks.

FIELD OF THE INVENTION 
This invention relates to magnetic stripe encoders and more particularly to 
hand swipe single and multi-track encoders. 
BACKGROUND OF THE INVENTION 
Single and multi-track, magnetic stripe encoders are in widespread 
commercial use. Such encoders are adapted to write on selected tracks on 
the stripe depending on the design and position of the write head. Writing 
occurs by the activation and positioning of a single gap write head with 
respect to the selected track and by the activation of the coil 
corresponding to the selected gap of a single or multi-gap write head 
corresponding to the track(s) to be written. 
Many encoders are table top motorized apparatus into which a card is 
inserted for encoding. With apparatus of this type, previously encoded 
data are on tracks adjacent to the track being encoded not exposed to the 
risk of being overwritten. This is not the case for hand swipe encoders, 
where the card is swiped manually through the encoder and card 
registration is accomplished by hand. In such cases the write head is 
positioned to encode on a magnetic track when the card is positioned in a 
vertical plane with its edge moving along a reference surface. Often the 
card is not seated properly against the reference surface when swiped and 
track misalignment results. Often, also, previously written data on a 
track adjacent to the selected track is destroyed. 
BRIEF DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT OF THIS INVENTION 
The present invention is directed at the prevention of erroneous encoding 
of a wrong track because of card misalignment in hand swipe encoders. 
Misalignment occurs because of improper seating of a magnetic stripe card 
against a reference surface in the encoder. This results in an edge of the 
card being at an angle with respect to the reference surface. Thus, the 
tracks are non-parallel to the reference surface, with which the write 
head is aligned causing data to be written into a non-selected track. A 
sensing device, located in line with the write head gap(s), senses when 
the edge of the card is elevated more than a preset distance from the 
referenced surface. The sensing device responds to apply a signal to the 
write circuit to turn the encoding current off.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT OF THE INVENTION 
FIG. 1 shows a top view of a credit card encoder 10. The encoder includes a 
slot 12 defined between side walls 14 and 15. A card to be read and 
encoded by the unit is inserted into slot 12 and moved between the side 
walls. 
FIG. 2 shows an end view of encoder 10 showing a bearing surface at the 
bottom of the slot. The bearing surface is defined by the portion of plate 
16 exposed between side walls 14 and 15. A credit card 17 properly seated 
against the bearing surface has its (multi-track) magnetic stripe defined 
in a vertical plane such that write Head 20 and read heads 21 and 22 
contact the magnetic stripe consecutively as the card is moved form right 
to left as viewed on FIG. 1. 
The encoder of FIG. 1 along with its component mechanical organization and 
electronic circuitry is well understood in the art and is not discussed in 
detail. The present invention is directed at the problem of encoding, for 
example, on a multi-track, magnetic stripe card which is not fully seated 
against the bearing surface. In such a circumstance, the tracks are at an 
angle to the gaps in the write head and write currents may result in the 
deleterious encoding of portions of tracks other then the selected track. 
FIG. 3 is a schematic side view of the encoder of FIG. 1. The figure shows 
the write head 20 and read heads 21 and 22. The figure also shows a lever 
arm 30. Arm 30 has an end 31 extending upward through bearing surface 
plate 38 as shown in detail in FIG. 4. That portion 31 extends into slot 
12 in a manner to contact the bottom of card 17 when the card is properly 
seated against the bearing surface. 
Lever arm 32 has a forked end portion 33 shown also in FIG. 2. Forked end 
portion 33 defines an opening 34. Arm 30 pivots at 35, indicating a 
fulcrum for the arm. Arm 32 is biased by spring 37. The spring is 
operative to bias the arm upward so that portion 31 extends above the 
bearing surface when no load is applied. 
Opening 34 is normally positioned to interrupt the optical path between a 
light source and a light sensor where the path is clear only when lever 
arm is forced downward by a properly seated card. A light sensor responds 
to the presence of light in the path to enable the write circuit. Thus, 
the write circuit is operative to write onto a selected track of the 
magnetic stripe only when a card is properly seated against the bearing 
surface and the tracks are aligned along axes parallel to the bearing 
surface and perpendicular to the write head gaps. Forked end 33 is spaced 
apart from the fulcrum a distance four times the distance between fulcrum 
36 and portion 31 to provide amplification to the movement of end 33 for 
occluding the optical path. 
FIG. 5 shows a circuit schematic for the write circuit which provides 
current to the write head. A single track head is indicated. The coil for 
the gap for a single track is connected between the lines designated 50 
and 51. Write enable and write signal levels are maintained at inputs 53 
and 54 respectively. A write enable voltage level is maintained at an 
input to OR circuit 56. A write protect voltage level is maintained on a 
second input to OR circuit 56 only if a card is properly seated against 
the bearing surface (i.e., portion 31 of lever arm 30 is flush to surface 
38). OR circuit 56 provides an output to disable the write operation if 
either input is high. 
A light-emitting diode (LED) 58 and phototransistor 59 pair are optically 
coupled via opening 34 of FIG. 4, lever arm 30 moving in a vertical plane 
indicated by broken line 60 in FIG. 5. The presence of light on transistor 
59 results in a high voltage level on line 61. When such a high level 
occurs along with a write enable level, OR circuit 56 provides an output 
disabling the write circuit so that no write current is applied to a 
selected coil about the pole pieces of a gap in the encode head to write 
onto the corresponding track. 
The write circuit for a single track is shown for generating write pulses 
of first and second polarities as is common. Such circuits include 
inverters 70, 71 and 72 and OR circuit 73 and 74, to provide pulses of the 
requisite polarities in coil 77. The circuit is repeated for providing 
pulses of the requisite polarities for each of the coils associated with 
the air gaps for each track. 
The invention is directed primarily a medium having a plurality of tracks 
on it's magnetic stripe. Standard ANSI and ISO formats allow a "guard 
band" of 0.020" between tracks 1 and 2, and 0.030" between tracks 2 and 3. 
Encoding from either track is allowed on the guard-band because the read 
head(s) are located so that they do not attempt to read in the guard band. 
Accordingly, hole 38 is sufficiently large to permit writing even if 
slight elevation of the card from the reference plate occurs. Elevations 
of 0.01", for example, are permitted. This allows for small imperfections 
in the reference plate and or magnetic stripe media. 
FIGS. 6 and 7 show a representative card with a multi-track, magnetic 
stripe in properly seated and improperly seated positions respectively. 
FIGS. 8 and 9 show the detail of adjacent tracks and gap positions. A 
multi-gap, write head is shown also to demonstrate the positions of the 
write head gaps with respect to the magnetic stripe in each instance. The 
gaps are designated by lines 70 and 71 in FIGS. 8 and 9. The tracks are 
designated 74 and 75. It is clear that erroneous overwriting occurs in the 
second instance because a write current in the coil associated with track 
75 writes on a portion of track 74 as is clear from FIG. 9. But in such 
circumstances (as shown in FIG. 9) lever arm 30 is not depressed, the 
optical path through opening 34 of FIG. 4 is occluded and no high level 
output is present on line 61 of FIG. 5 to enable OR circuit 56. 
Consequently, the write signal is not applied to the selected coil and no 
write operation occurs.