HP HP-97 User Manual

HP-97 Theory of Operation
2-25. Print Head Drivers
2-26. Each head resistor requires approximately 0.5A of current to
adequately print on the heat sensitive paper. NPN transistors Q1 through
Q7, driven by the PIK, act as switches to supply the head resistors with
the required current and also to reduce the drive requirements from the
PIK.
[
I ]
] Printed 'ONE’
]
]
]
I ]
" Head moves right to
left while printing.
Figure 2-7. Printed Character
2-27. Printer Motor Control
2-28. A small dc motor provides the mechanical power through the action of
the lead-screw and gears to move the print head. Current for the motor is
controlled by the on and off action of six driver transistors Q9 through
Q14.
2-29. When the PIK gives the command to move forward, transistors Q11, Q14,
and Q9 turn on. Transistors Q12, Q13, and Q10 turn on to reverse the
direction of head travel.
2-30. Braking action is produced by shorting the dc motor windings; when
Q8 is turned on, it shorts the windings and Q10 provides a signal ground for
the base current from Q8.
2-31. The printed line width and character-to-character spacing is
determined by the speed of the dc motor. To control the speed of the motor,
U4 samples the output voltage generated by the motor when the driver
transistors are turned off and the motor is coasting. Contained within U4 is
2=T

HP HP-97 Specifications

General

Brand	HP
Model	HP-97
Category	Calculator
Language	English