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  1. Member
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    Hi!

    I'm using CGA to VGA converter with RGBI digital.
    Cable which connects to adapter is DB9 > DB15 (VGA) has not connected intensity.
    This is for digital RGBI loosing 8 colors - all dark colors are displayed as light.
    My friend created for me cable with connected intensity, but signal is weak and I must to force up brightness, contrast, color adjust to get at least stable picture.

    Q is: Exist any device to increase signal strength to display correct image?

    Thank you for all.
    Miro
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  2. To get a proper display I think you need an active device like:
    http://www.raphnet.net/electronique/cga2vga/index_en.php
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  3. Member
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    I try to contact them.
    Miro
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  4. Note that the development board costs about US$150 to US$250 depending on where you get it from.
    https://www.altera.com/support/training/university/boards.html#de1-soc
    https://www.digikey.com/products/en?keywords=altera%20de1

    And then you'll need to learn how to program the device. That may require additional hardware.
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  5. Member
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    I know price, even I'm using Nexys4DDR FPGA, MiST FPGA computer.
    Altera DE1 can be used even for other projects.
    I'm beginner in VHDL, but I have time to learn.
    Maybe they provide code - and if - for me it will be example from I can learn anything new.
    Miro
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  6. There was a link to the project's source at raphnet.net.
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  7. Perhaps ready to use GBS8200 will be OK for you?
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  8. Definitely worth a try, given the low price.
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  9. Member
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    So, I decided to ask again for signal strength increasing device.
    Both suggested solutions have not solved flickering with interlaced modes.
    And my CGA2VGA converter flickering removes - outputs stable picture, but picture is weak.

    So, Q again: Exist any device which increases signal strength?

    Miro
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  10. I believe a lot of VGA distribution amplifiers and repeaters have gain controls to account for voltage drops through long cables. For example:
    http://www.extron.com/product/product.aspx?id=p2da1
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  11. Member
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    That looks good!

    Thank you!
    Miro
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  12. Have you looked at your VGA output with an oscilloscope to verify the voltage levels are too low? I'm not fully convinced that's the real problem.
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  13. Originally Posted by MIRKOSOFT View Post
    So, I decided to ask again for signal strength increasing device.
    Both suggested solutions have not solved flickering with interlaced modes.
    And my CGA2VGA converter flickering removes - outputs stable picture, but picture is weak.

    So, Q again: Exist any device which increases signal strength?

    Miro
    CGA produce TTL signals - they are converted in very simple/crude DAC (few resistors) - such signal has very high amplitude compared to normalized VGA signal (usually from 0 to 1 V) - IMHO your CGA conversion is improper (signal should be too high for VGA).
    Firstly i would address proper RGBI/CGA to Analogue/VGA conversion - this may remove necessity for signal amplifier - verify this circuit http://www.electroschematics.com/377/cga-scart-adapter/ .
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  14. Member
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    Ok, for explain:

    I own CGA2VGA converter which convert it as RGB analog instead RGBI digital.
    It's cable has this connections (not connected internsity)

    Click image for larger version

Name:	cable_scheme.png
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ID:	41129

    Friend created for me similar cable like on link - connection of intensity with regulation of R,G,B, I, H,V...

    Click image for larger version

Name:	pull-both-vga.jpg
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ID:	41130

    Converter has built-in deinterlacing and provides always stable picture - original cable displays 8 colors 'cause missing intensity and clear nice picture, but if I want 16 colors, I must to connect cable from friend - adjusting controls affecting also deinterlacing so there is not so big area to adjust it and signal stays weak...
    So, I think it requires signal strength increase.

    Please correct me if I'm not true.
    Miro
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  15. 2 Si diodes may give you approx 2.4V drop, - TTL level usually is around 3.6 - 4V - it may be problem with too high signal level not too low - Use oscilloscope and verify level of signal - oversteered amplifier (saturated) may give results that can be confused with too low signal level if some form of AGC is involved.

    Personally i would prefer to use different CGA DAC than yours - if you don't have oscilloscope simulate your DAC in Spice - you will see why.
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  16. Member
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    Problem - I'm not able to work with oscilloscope and even in electronic I'm moron - don't know anything...
    ...
    To other adapters:
    All other adapters flickering in interlaced mode - my adapter removes flickering and has else one benefit.
    I'm using CGA2VGA for my Commodore 128, I'm programmer and user.
    It's used for VDC circuit output what is RGBI digital, we are trying to force up to 1280 pixels horizontally instead normal maximum 800 pixels. Normal CRT for C128 it cannot display - there it's around 800 pixels, but my adapter has best results in 1280x200...
    So, I don't want to use other.

    How to do anything without any electrotechnic knowledge?
    Really want to ask: exists any device to adjust VGA signal brightness, saturation, hue, colors, R, G, B and so on without convert signal into other?
    Many adapters exists doing it but it is in 99,9% cases converting VGA to composite or S-Video.
    Really adapter only adjusting signal and not changes other.

    Thank you.
    Miro
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  17. I have an Arduino and enough parts sitting around to create the resistor/diode circuit in post #14.

    Image
    [Attachment 41134 - Click to enlarge]


    I used a 82 ohm resistor as the load on the output (closest I had to 75). I used 1N5817 Schottky diodes (that's all that I have on hand). I checked the resistors with my multimeter and they were within about 1 percent. I used a 100 MHz scope to view the output.

    Using 5 volt inputs I get the following outputs:
    Code:
    RED INT  OUTPUT
    ---------------
     0   0   0.01 V
     1   0   0.26 V
     1   1   0.60 V
     0   1   0.28 V
    Any time INT is high there is significant (~50 mV) high frequency (~28 MHz) ringing on the output. There's also a short overshoot to about 2V when INT switches from low to high.

    This Arduino has the option to run at 3.3V where I get:
    Code:
    RED INT  OUTPUT
    ---------------
     0   0   0.01 V
     1   0   0.21 V
     1   1   0.40 V
     0   1   0.18 V
    This circuit is also very sensitive to the monitor's input impedance. Don't expect the same brightness/colors on different monitors.
    Last edited by jagabo; 4th Apr 2017 at 17:26.
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  18. Member
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    All what I can write to 3,3V vs 5V:

    Copy from manual:

    Power Supply:
    AC Input: 110V-240V 50-60Hz
    DC Output: DC 3.3V, 1.5A, center positive

    Input RGB Signals:
    RGB: 0.7 Vp-p 75 ohm
    H sync/ V sync: 2 Vp-p 75 ohm
    YCbCr: 1 Vp-p(Y), 0.7 Vp-p 75 ohm(CbCr)

    So, helps it or P/2 DA1 is solution?
    Miro
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