Browse Prior Art Database

Character Generator for Tilted LED Arrays

IP.com Disclosure Number: IPCOM000088546D
Original Publication Date: 1977-Jun-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 67K

Publishing Venue

IBM

Related People

Levine, JL: AUTHOR

Abstract

The subject disclosure describes a novel means of deriving control signals to display alphanumeric information with tilted arrays of light-emitting diodes (LEDs) in rotating optical light-emitting diode (ROLED) displays. It is shown that there is no need for information storage associated with each LED and that a simple modified character generator can feed the tilted arrays as readily as a standard character generator can feed a linear array.

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Character Generator for Tilted LED Arrays

The subject disclosure describes a novel means of deriving control signals to display alphanumeric information with tilted arrays of light-emitting diodes (LEDs) in rotating optical light-emitting diode (ROLED) displays. It is shown that there is no need for information storage associated with each LED and that a simple modified character generator can feed the tilted arrays as readily as a standard character generator can feed a linear array.

Fig. 1 shows an array of LEDs formed of groups of 5 LEDs tilted at an angle Phi. The LEDs are assumed to be individually addressable, matrix addressing can be handled by an obvious extension of the technique. The array will be viewed through a scanning device (not shown), which scans in the direction indicated in Fig. 1. Typically, the scanning device may be a rotating mirror or prism. The format of a character in 5x7 font is illustrated in Fig. 1, for reference purposes.

Character generator 1 is a read-only memory (ROM) containing the character font. It produces a 5-bit output word, representing one row of a character, one 5- bit input word selecting one of 32 characters and one 3-bit word selecting a row in the character. The 8th row produces logical zeros for insertion of blank lines. One complete display line (raster line) is set up by loading 5-bit words into long shift register 3, the contents being moved in parallel to latch circuits 5 when the shift register is full. Information for the next line is loaded while the previous line is displayed. The latch circuits are cleared to terminate the light pulses at a time chosen to limit blurring of the images. It is clear that the arrangement would work properly if the LEDs were arranged in a straight line.

With the tilted arrangement, whose useful properties have been discussed elsewhere, the arrangement will not work; the characters will clearly appear tilted at the angle of the array. This can be corrected by a number of cumbersome (and expensive) techniques involving large numbers of shift register delays, special refresh memories, etc. Instead, this article describes a simple arrangement based on a special character generator which can directly replace generator 1 of Fig. 1. Such a generator will consist of a read-only memory containing the usual character information, but with a modified addressing scheme whose function will be described below.

Fig. 2 shows a portion of the desired display grid (dots), some LEDs (open circles), and 3 characters (filled circles). A 5x7 font is assumed, and 3 grid spaces are left between characters. The tilt angle Phi = arctan (2) is chosen such that the vertical pitch of the array is twice the vertical pitch of the display grid. Other choices are possible (Phi = arctan (N), with N an integer). To understand the operation of the special character generator, it is helpful to trace the LED locations onto a plastic sheet. The action of the scanner may be visualized...