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Browse Prior Art Database

Automatic Microprocessor Control of Monitor Degauss Function

IP.com Disclosure Number: IPCOM000114202D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 155K

Publishing Venue

IBM

Related People

Eagle, DJ: AUTHOR [+2]

Abstract

Large screen monitors of 17 inches or more are more susceptible to color purity distortion of the screen image, caused by build up of magnetism on the ferrous parts of the monitor chassis, than small screened monitors. The usual solution to this problem is to add a manual user degauss button on the control panel. This supplements the power-on degauss.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 40% of the total text.

Automatic Microprocessor Control of Monitor Degauss Function

      Large screen monitors of 17 inches or more are more susceptible
to color purity distortion of the screen image, caused by build up of
magnetism on the ferrous parts of the monitor chassis, than small
screened monitors.  The usual solution to this problem is to add a
manual user degauss button on the control panel.  This supplements
the power-on degauss.

      However, with the advent of multi-stage power saver functions,
many users now leave their monitors powered on 24 hours a day.  As a
result of this, the monitor manufacturer is dependant on the users'
awareness of the monitor's controls and on them recognising this
Front Of Screen (FOS) problem so as to remember to use the manual
degauss button.  The user must do this to maintain optimum FOS
performance.  If a monitor has no manual degauss facility at all then
the user must switch the unit off to allow it to cool thus causing an
inconvenience.  It is unlikely that the average user will be aware of
this and customer dissatisfaction will result.

      The following scheme demonstrates how it is possible to
automate this function and so prevent customer product
dissatisfaction whilst still permitting the user to degauss when
required.  In addition to solving this problem this scheme allows
intelligent degauss operation and prevents a common problem
associated with some manual degauss circuits.

      The key to this scheme and so to the solution of this problem,
is to place automatic control of the degauss function with the
on-board microprocessor.  Many monitors now contain a microprocessor,
which controls most monitor functions.  The microprocessor sends its
'degauss' signal across the primary/secondary gap and so controls the
degauss circuitry.  One possible circuit has been built and tested
and is now described.

      The attached circuit diagram shows how the microprocessor
controlled degauss function may be incorporated into a monitor.  The
actual degauss action is achieved using a standard technique; current
is taken from the mains supply LIVE and flows through the degauss
coil itself, then through a triac and finally through a PTC element
which heats and causes the current flow to decay.

      The main triac is triggered by an opto-triac switching on to
allow current to flow into its gate.  The opto-triac is switched on
by pulling its LED cathode LOW.  This action is initiated by the
microprocessor but is buffered by a pnp transistor.  The trigger
pulse is taken from an output pin on any suitable microprocessor.
The pulse duration is set at around 300mseconds to ensure a complete
degauss, further degauss should be locked out or prevented by the
micro's software for at least five minutes.  This particular
configuration requires an active LOW trigger pulse from the micro.

      With the degauss function under control of the micro, normal
operation is easily maintained. ...