Browse Prior Art Database

Digital Encoding of Joystick Position

IP.com Disclosure Number: IPCOM000087649D
Original Publication Date: 1977-Feb-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Holloway, BL: AUTHOR

Abstract

In an interactive display terminal, a joystick or similar device can be used to move a cursor around the display screen. The direction in which the cursor is moved depends upon the movement of the joystick. Sometimes, the speed of movement depends on the degree of deflection of the joystick. Typical joysticks have their motion resolved into X and Y directions by means of attached potentiometers; the resistance of the potentiometer is proportional to the deflection of the joystick.

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Digital Encoding of Joystick Position

In an interactive display terminal, a joystick or similar device can be used to move a cursor around the display screen. The direction in which the cursor is moved depends upon the movement of the joystick. Sometimes, the speed of movement depends on the degree of deflection of the joystick. Typical joysticks have their motion resolved into X and Y directions by means of attached potentiometers; the resistance of the potentiometer is proportional to the deflection of the joystick.

Fig. 1 shows a circuit for converting the resistance into a digital value. In practice one circuit would be used for each of two orthogonal directions. Single- shot 1 has capacitor 2 and fixed resistor 3 connected as part of its timing circuit. In addition, potentiometer 4, whose resistance is a measure of the deflection of the joystick, is connected in the timing circuit of single-shot 1. Output 5 of single- shot 1 is used to gate pulses for oscillator 6 through AND gate 7 into binary counter 8. The count in counter 8 can be read out to graphics processor 9 which controls movement of the cursor on the display screen.

Thus when single-shot 5 is triggered, it will give an output pulse whose length will depend upon the resistance of potentiometer 4. The number of oscillations gated through AND gate 7 into counter 8 will depend upon the duration of the single-shot output.

Fig. 2 is a timing diagram showing the relationship between the various pulses an...