GB2102944A

GB2102944A - Light pen arrangements

Info

Publication number: GB2102944A
Application number: GB8220831A
Authority: GB
Inventors: Keith Patrick Jones
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1981-07-20
Filing date: 1982-07-19
Publication date: 1983-02-09
Also published as: GB2102944B

Abstract

In or for an interactive visual display system comprising a raster scan visual display unit 2, a length of optical fibre 6 is used as a light pen, the optical fibre having a sleeve at one end acting as the "pen" 1 and an electric circuit at the other end responsive to light signals picked up from the screen of the visual display unit. The system may employ a character recognition arrangement. <IMAGE>

Description

SPECIFICATION Light pen arrangements The present invention relates to light pen arrangements.

Light pens may be used for example in arrangements for sketching directly onto visual display units, or onto the screen of domestic television receivers.

The screen of the display unit or television receiver may be considered as comprising an array of contiguous areas or picture elements in each of which may be displayed any one of a set of, say, one hundred and twenty eight different graphic characters. A sketch is made up by sensing from successive light pen positions within a picture element which character of the set is to be displayed in that picture element.

With the sketch reduced to using only members of the graphic character set an assembled sketch may readily be transmitted at a low data rate, for example over a telephone network, to make possible applications such as 1) telephone for the deaf, transmitting text messages, 2) setting up and transmitting engineering or electrical drawings or modifications, or 3) in domestic use for communicating line drawings or other sketches such as route maps.

According to one aspect of the present invention a light pen arrangement comprises a length of optical fibre, manually operable means at one end of said fibre to position the said end and electric circuit means at the other end of said fibre responsive to the level of light energy transmitted by said fibre from said one end.

Preferably said manually operable means comprises a generally tubular sleeve surrounding said optical fibre.

According to another aspect of the present invention an interactive visual display arrangement comprises a raster scan visual display unit, a length of optical fibre, manually operable means at one end of said fibre to position said one end with respect to the display screen of said visual display unit, and electric circuit means at the other end of said fibre responsive to the level of light energy transmitted by said fibre from said display screen to provide an indication of the position of said one end with respect to said display screen.

Preferably said electric circuit means is responsive to provide said indication whenever the raster scan of said display screen passes said one end of said fibre.

A light pen arrangement in accordance with the present invention will now be described with reference to the accompanying drawings, of which: Figure 1 shows schematically an interactive terminal, and Figure 2 shows diagrammatically a detector circuit for the terminal of Figure 1.

Referring first to Figure 1 the light pen 1 may be used in conjunction with a video display unit 2 to form an interactive terminal, for use with, say, a Prestel/Viewdata system. The pen 1 may be used to "draw" on the screen of the display unit 2 any one of a set of graphic characters in any of a matrix of areas on the screen, whereby a desired picture may be built up on the screen.

The detector circuit shown in Figure 2 is used to provide a timing pulse indicating the position of the tip of the pen on the screen, as will be described, and the position indication is entered in a memory field (not shown) in a system controller 3. As the tip of the pen 1 is moved over an area of the screen to describe one of the set of graphic characters the changing position indications are entered in the memory field, and a character recognition arrangement (not shown) is utilised to determine which of the set of characters has been described by comparison with standard representations of these characters held in a read only memory (not shown). When the character being drawn has been recognised it may be displayed on the respective area of the screen, in its standard form, or may be made available for transmission over a telephone link 4 associated with a telephone set 5.

The light pen 1 comprises a length of optical fibre 6, say one to three metres long, the free end of which is enclosed in a tubular protective sleeve by means of which this free end may be handled without damage. The other end of the fibre 6 is coupled to a PIN photo diode 7 in an input circuit of an operational amplifier 8 the other input circuit of which is provided with a threshold voltage from a potential divider 9.

The amplifier 8 provides an output pulse each time the raster scan of the display unit 2 passes the free end of the optical fibre 6, and this output pulse is used to illuminate a light emitting diode 10 and to indicate to the system controller circuits (not shown) where the free end of the fibre 6 is in relation to the raster scan timing.

For a standard visual display screen capable of displaying 32 rows each of 52 characters an optical fibre having an aperture of, say, 0.124 will be able to resolve individual dot elements of the eight by eight dot matrix used to define a character, since the end of a fibre 6 of this aperture placed against the outer face of the screen will receive light only from an area of the phosphor on the reverse face equivalent to one "dot".

The light emitting diode 10 provides an indication that the position of the light pen 1 is being detected, since it will then be illuminated each time the raster scan passes the tip of the pen 1. This may be used to set the background brightness of the display screen.

Claims

1. A light pen arrangement comprising a length of optical fibre, manually operable means at one end of said fibre to position the said end and electric circuit means at the other end of said fibre responsive to the level of light energy transmitted by said fibre from said one end.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Light pen arrangements The present invention relates to light pen arrangements. Light pens may be used for example in arrangements for sketching directly onto visual display units, or onto the screen of domestic television receivers. The screen of the display unit or television receiver may be considered as comprising an array of contiguous areas or picture elements in each of which may be displayed any one of a set of, say, one hundred and twenty eight different graphic characters. A sketch is made up by sensing from successive light pen positions within a picture element which character of the set is to be displayed in that picture element. With the sketch reduced to using only members of the graphic character set an assembled sketch may readily be transmitted at a low data rate, for example over a telephone network, to make possible applications such as 1) telephone for the deaf, transmitting text messages, 2) setting up and transmitting engineering or electrical drawings or modifications, or 3) in domestic use for communicating line drawings or other sketches such as route maps. According to one aspect of the present invention a light pen arrangement comprises a length of optical fibre, manually operable means at one end of said fibre to position the said end and electric circuit means at the other end of said fibre responsive to the level of light energy transmitted by said fibre from said one end. Preferably said manually operable means comprises a generally tubular sleeve surrounding said optical fibre. According to another aspect of the present invention an interactive visual display arrangement comprises a raster scan visual display unit, a length of optical fibre, manually operable means at one end of said fibre to position said one end with respect to the display screen of said visual display unit, and electric circuit means at the other end of said fibre responsive to the level of light energy transmitted by said fibre from said display screen to provide an indication of the position of said one end with respect to said display screen. Preferably said electric circuit means is responsive to provide said indication whenever the raster scan of said display screen passes said one end of said fibre. A light pen arrangement in accordance with the present invention will now be described with reference to the accompanying drawings, of which: Figure 1 shows schematically an interactive terminal, and Figure 2 shows diagrammatically a detector circuit for the terminal of Figure 1. Referring first to Figure 1 the light pen 1 may be used in conjunction with a video display unit 2 to form an interactive terminal, for use with, say, a Prestel/Viewdata system. The pen 1 may be used to "draw" on the screen of the display unit 2 any one of a set of graphic characters in any of a matrix of areas on the screen, whereby a desired picture may be built up on the screen. The detector circuit shown in Figure 2 is used to provide a timing pulse indicating the position of the tip of the pen on the screen, as will be described, and the position indication is entered in a memory field (not shown) in a system controller 3. As the tip of the pen 1 is moved over an area of the screen to describe one of the set of graphic characters the changing position indications are entered in the memory field, and a character recognition arrangement (not shown) is utilised to determine which of the set of characters has been described by comparison with standard representations of these characters held in a read only memory (not shown). When the character being drawn has been recognised it may be displayed on the respective area of the screen, in its standard form, or may be made available for transmission over a telephone link 4 associated with a telephone set 5. The light pen 1 comprises a length of optical fibre 6, say one to three metres long, the free end of which is enclosed in a tubular protective sleeve by means of which this free end may be handled without damage. The other end of the fibre 6 is coupled to a PIN photo diode 7 in an input circuit of an operational amplifier 8 the other input circuit of which is provided with a threshold voltage from a potential divider 9. The amplifier 8 provides an output pulse each time the raster scan of the display unit 2 passes the free end of the optical fibre 6, and this output pulse is used to illuminate a light emitting diode 10 and to indicate to the system controller circuits (not shown) where the free end of the fibre 6 is in relation to the raster scan timing. For a standard visual display screen capable of displaying 32 rows each of 52 characters an optical fibre having an aperture of, say, 0.124 will be able to resolve individual dot elements of the eight by eight dot matrix used to define a character, since the end of a fibre 6 of this aperture placed against the outer face of the screen will receive light only from an area of the phosphor on the reverse face equivalent to one "dot". The light emitting diode 10 provides an indication that the position of the light pen 1 is being detected, since it will then be illuminated each time the raster scan passes the tip of the pen 1. This may be used to set the background brightness of the display screen. Claims

2. A light pen arrangement in accordance with Claim 1, wherein said manually operable means comprises a generally tubular sleeve surrounding said optical fibre.

3. An interactive visual display arrangement comprising a raster scan visual display unit, a length of optical fibre, manually operable means at one end of said fibre to position said one end with respect to the display screen of said visual display unit, and electric circuit means at the other end of said fibre responsive to the level of light energy transmitted by said fibre from said display screen to provide an indication of the position of said one end with respect to said display screen.

4. An arrangement in accordance with Claim 3, wherein said manually operable means comprises a generally tubular sleeve surrounding said optical fibre.

5. An arrangement in accordance with Claim 3 or Claim 4, wherein said electric circuit means is responsive to provide said indication whenever the raster scan of said display screen passes said one end of said fibre.

6. A light pen arrangement substantially as hereinbefore described with reference to the accompanying drawings.