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Forum Index : Microcontroller and PC projects : Pondering a way of dimming a VGA screen in MMBasic
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OA47 Guru  Joined: 11/04/2012 Location: AustraliaPosts: 992 |
If I were to dim a LCD screen I can use the BACKLIGHT command But when I use a VGA LCD the only way I can think of dimming a screen (mainly of TEXT) is to have a matrix of colours for full brightness and dimmed text selected in the TEXT command. Is there a simpler way of accomplishing this so that on darkness I can dim the display? OA47 |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 8041 |
I can't think of a way. The VGA colour outputs are either off or on and are a binary counter. There are no intermediate stages so nothing can be dimmed. You could use colour palettes on a HDMI display, but not on VGA as the colours are fixed by the resistor values. One idea would be to use monochrome VGA, in which case you have 16 shades of a single colour. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5193 |
OA47 Most VGA monitors have a brightness setting (either a knob (CRT) or a menu setting (LCD). In the PicoMite VGA there is a hardware RGB driver, that canNOT be manipulated with software. Selecting Yellow (Amber) or green as ink color can help a bit in dimming in a monochrome display. One possible hardware solution could be to create a VGA cable with 50 or 100ohm resistors in R,G and B lines (series), but leaving the HSYNC and VSYNC unaltered. For a special application, you could make such a special cable, potentially even with a switch to bypass the resistors and return to full brightness. Volhout PicomiteVGA PETSCII ROBOTS |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2678 |
Many if not most VGA monitors have a button to bring up a settings menu. If yours doesn't hardware is the only option. 3 series resistors and a triple pole switch to short them out is one way. 3 logic level N ch. MOSFETs instead of the switch controlled by a DOUT is as close as you will get to a software solution. Edit Too slow! Edited 2025-08-25 18:20 by phil99 |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 992 |
I understand the hardware options given but I would like the mite to operate the dim when external light is low. OA47 |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2678 |
An LDR could control the gates automatically. Either directly or via an AIN that gets polled periodically. |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 992 |
Maybe the option could be 16 colour daytime and monochrome nighttime? OA47 |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2678 |
Myrtle is the dimmest RGB121 colour. There are no greys in RGB121 so monochrome is just black and full brightness white. Greyscale can only be done with extra hardware. Some time ago I made and described here a plug-in module for greyscale. |
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| OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 992 |
My next thought for simplicity might be to use the Myrtle colour as Phil suggested for all text during the sundown time and bring back full colour during daylight. I had intended to show red text where a value has been detected as out of order so I may still do this when the sundown display is shown. OA47 |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5193 |
OA47, If you design something yourself, in the night display, you can also use RGB(GREEN) (saturated green) as the focus color, while RGB(MYRTLE) is the default color. Volhout PicomiteVGA PETSCII ROBOTS |
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