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DVI or HDMI shield with true color output: 4.3" plugin works too

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  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    I think Lawson is right about the resistor DAC for VGA....

    I just made the regular 6-bit Parallax DAC using 470 and 240 Ohm resistors resistors soldered onto the 40-pin header in the center of the board.
    Then, using the DVI to VGA adapter (that comes with most PC video cards), I get nice regular VGA on my monitor.

    It looks OK, but you can tell it's only 6-bit... But, I'm sure it'd look better with more resistors...
    VGA_wResistors.jpg


    Was just wondering if I'm making a mistake by not using 240 Ohm resistors on the VSync and HSync signals like Parallax does...
    Quick web search makes it appear the sync signals are TTL inputs to the monitor, so I think I'm OK without them...

    Update: Just added 3 more bits with some 1.1 k resistors (not sure if that's the right value) and it looks much better.
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  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    I just made the regular 6-bit Parallax DAC using 470 and 240 Ohm resistors resistors soldered onto the 40-pin header in the center of the board.

    Does the SSD1963 manage ok with a 240 ohm load ?
    Or does it disturb it enough the DVI suffers ?
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Seems to work... Output is rock solid... Don't see anything in the datasheet in this respect... Maybe I should let it run like this overnight and see if it survives...
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  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    Seems to work... Output is rock solid... Don't see anything in the datasheet in this respect...
    Have you got a good scope ? - check how much Voh is pulled down by that load ?
  • Roy ElthamRoy Eltham Posts: 2,273
    edited March 2012 Vote Up0Vote Down
    Awesome Ray! Will you have some for sale at the Parallax Expo (UPEW) this year?
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 21,901
    edited March 2012 Vote Up0Vote Down
    Ray,

    The Parallax resistor values are not optimal and could lead to saturation. Please see this thread for clarification and suggestions for improvement:

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    I'm definitely going to be sad if I don't have some ready before the expo...
    I think I have the board design done (there were a couple errors and tweaks to do).
    But, now I'm trying to piggyback other boards onto this PCB order to minimize setup costs...

    My current thought about VGA output is to use an 8-bit 10k/20k R2R ladder (available as a single chip) for each color and then use a 3-channel video amp to drive the output....
    Prop Info and Apps: http://www.rayslogic.com/
  • jazzedjazzed Posts: 11,803
    edited March 2012 Vote Up0Vote Down
    Hey Rayman. Nice work so far. I look forward to a live demo.
    Thanks,
    --Steve
  • CircuitsoftCircuitsoft Posts: 1,001
    edited March 2012 Vote Up0Vote Down
    Would the video amp have low-enough input capacitance for 10k/20k to work well? I imagine you'd want much lower resistances for video.
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Now you got me worried...
    Well, I think 10k/20k is OK but, I don't want to take any chances and box myself into a corner...
    On seccond thought, I'll just use a bunch of standard resistor networks...
    That way, I can switch values if I need to...
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  • CircuitsoftCircuitsoft Posts: 1,001
    edited March 2012 Vote Up0Vote Down
    Just make an R/2R ladder of 0402 or 0603 resistors, and you can swap them out for smaller values if need be. You may also want to drive them by a high-speed line driver buffer.

    You could also use a THS8134. It is $7.50 from DigiKey, but it's 3 converters with a parallel input, and would probably fit next to the TFP410 pretty easily.
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Something like that THS8134 does look like a much better solution for legacy VGA... Can't use that particular chip because it needs 5V and my expansion header only supplies 3.3V. But, there's a similar chip that will work.

    I don't know about putting this chip on the main board though. My feeling is that people who would spend the $ for this board would be most interested in DVI or HDMI output. And, if they needed VGA, the expansion board would work for them.

    Maybe later I'll do a full system board that has DVI, VGA, TV, USB, and MP3...

    Too bad the survey feature of the forum is gone... I'd really like to know how important having regular VGA along with DVI is to people interested in this... Would they rather have a $10 increase in the main board price or have VGA as an optional $15 accessory...

    Actually, it doesn't look all that bad with just my little resistor dac... If it were for graphics and not photos, it's perfectly acceptable. Maybe with a couple more resistors, photos would look pretty good too...
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  • BeanBean Posts: 7,845
    edited March 2012 Vote Up0Vote Down
    Rayman,
    Speaking just for me, I want HDMI as cheap as possible. I think you said a simple cable will convert from DVI to HDMI.
    I think an add-on for VGA would the way to go.

    Bean
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  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Thanks Bean. I've added a fourth resistor (2.2k) to my VGA resistor DACs and now the test pictures look reasonable,
    considering it's VGA and only 12 bits at best...:

    12bitRDAC.JPG
    12bitRDACa.JPG
    12bitRDACb.JPG
    12bitRDACc.JPG
    12bitRDACd.JPG


    Nowhere near as good as the HDMI, but still pretty good...

    Made some scope measurements for jmg... Seems the output resistance of the SSD1963 is about 36 Ohms.
    So, it does drop the voltage on the 240 ohm loaded color bits from 3.3V to 2.9V.
    Took a look at the sync signals too. They are loaded severely (1V) for 20 ns and then rise to 3.3V in about 50 ns.
    But, the board has been outputting VGA non-stop for 2 days now and hasn't died yet, so I think it's going to be OK...
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  • LawsonLawson Posts: 870
    edited March 2012 Vote Up0Vote Down
    I just pulled up the R-2R calculator I linked, and it looks like a network of 300 ohm and 560 ohm (560+ 36 from the pin = 596) resistors would work well assuming a 3.3v supply. Max voltage into a 75 ohm load would be ~.67 volts, and the glitch at the $7F to $80 transition looks less than one LSB. Should get 1% or better resistor, and each driving pin should only see ~1K ohm load. I'd vote for having unpopulated footprints for the R-2R DAC. If the resistors are 0805 or larger, they're easy to add if needed.

    Lawson

    http://www.brischalle.de/JDAC/DAC_R2R_network_calculation_en.html
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  • CircuitsoftCircuitsoft Posts: 1,001
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    Something like that THS8134 does look like a much better solution for legacy VGA... Can't use that particular chip because it needs 5V and my expansion header only supplies 3.3V.
    I picked that chip out, thinking of a 160MHz pixel clock. While the prop can do that, I guess the SSDxxx is more limited. As for adding cost for an unused feature, what about making it a noplace?
  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    Too bad the survey feature of the forum is gone... I'd really like to know how important having regular VGA along with DVI is to people interested in this... Would they rather have a $10 increase in the main board price or have VGA as an optional $15 accessory...

    Here's how I would cover all the bases :
    * Add a ADV7125 Footprint, (Check ADV7123 too?) but do not fit it on the cheapest offered PCB..
    * Add R/2R using 4 element 1206 package networks. 4 parts for 8 bits, 12 for 24b. (or 6 for 12b)
    Quote Digikey numbers for both, and have a price with all options fitted.

    Perhaps offer 6 networks fitted for free, and 12 on the +VGA build variant.

    ADi claims $2,89/1K for ADV7125KSTZ50, but strangely no distis get close to that.

    For me, I'd want both fitted, just to easily test/verify various monitors. Think 'reference point'.
    These include schematics / artwork ?
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    I'm almost finished laying out 2 plugin boards for this shield...
    One will be "Legacy VGA Adapter" and use the ADV7125 and have a VGA connector.
    Other one will have connectors for both the Newhaven and my 4.3" touchscreens...

    BTW: I'm glad the Prop Platform USB has a 1.5 A regulator for 3.3 V...
    It's warm now and it's going to get really toasty driving the backlight on the 4.3" LCDs...

    BTW2: The word "legacy" is kinda interesting... Both a compliment and an insult, really...
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  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    I'm almost finished laying out 2 plugin boards for this shield...
    One will be "Legacy VGA Adapter" and use the ADV7125 and have a VGA connector.
    Other one will have connectors for both the Newhaven and my 4.3" touchscreens...

    Do you have an update on this ?
    Does the comment above mean there will be a VGA _and_ DVI connector ?
    ie a LCD model, and a Monitor model ?
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Thanks for asking. I just got the boards in and I've also just ordered the stencil and the parts.
    Should be able to begin assembly next Tuesday.
    If they check out, they'll be for sale next week.
    I'm pretty sure the initial price will be $29.99 with maybe a $2 to $5 shipping charge.

    I have two prototype plugin boards for this module that connect via the central 40-pin connector.
    One will give you regular VGA with a 24-bit DAC. The other is for both Samsung and Newhaven 4.3" TFTs.
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  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    I have two prototype plugin boards for this module that connect via the central 40-pin connector.
    One will give you regular VGA with a 24-bit DAC. The other is for both Samsung and Newhaven 4.3" TFTs.

    Does the 'regular VGA' include TFP410/DVI (as in the fist page) and also ADV7125/HD15 ?

    That's I'd like to see; we have many HD15 Monitors here, but will likely change to DVI/HDMI long term, certainly on larger ones, and I'm keen on seeing just what the visible difference is. - and having a 'Dual connector Monitor-tester' appeals.

    I recently bought a new 'Cheapest LED backlight' model, and that was HD15 only, so that still looks like the 'lowest common denominator' will be HD15 for a while yet. Spoke to someone this morning, who got a larger one, that came with HD15 and DVI.
  • Don MDon M Posts: 1,570
    edited March 2012 Vote Up0Vote Down
    Ray- You going to bring some along for sale at UPEW next month?
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Right now, you'd need the new plug-in board to get regular (HD15 connector) vga. Or, you could use a bunch of resistors, like I did above, to do an adequate job. The plug-in board will make VGA near perfect though, not just OK.

    If the VGA plug-in board actually works, then I'll scope out the demand for a version of the main board that does VGA instead of DVI/HDMI.
    It could be that I'm a few years too early and most people would rather have plain analog VGA...

    Don, I'm trying very hard to have them ready for UPEW...
    As long as I didn't mess up the circuit board, we should be OK...
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  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    Right now, you'd need the new plug-in board to get regular (HD15 connector) vga. Or, you could use a bunch of resistors, like I did above, to do an adequate job. The plug-in board will make VGA near perfect though, not just OK.

    If the VGA plug-in board actually works, then I'll scope out the demand for a version of the main board that does VGA instead of DVI/HDMI.
    It could be that I'm a few years too early and most people would rather have plain analog VGA...

    Ah, so this is a plug-in on top of a plug-in ?

    Can you not fit both chips/connectors on the first plug in, and then assemble either/both ?
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Having both the DVI/HDMI output chip and the VGA DAC chip both connected to the SSD1963 on one board should be possible.
    It will be a bit of a layout issue, but maybe not too bad. But, I think for right now, I'm going to focus on getting these boards working.
    Then, maybe look at where to go next... Maybe a Quickstart plug-in board with both VGA and DVI output...
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  • tdg8934tdg8934 Posts: 123
    edited March 2012 Vote Up0Vote Down
    Ray,

    This sounds like a great acheivement. I'll be following this thread to see when they will be available. I'll buy one for sure. Great idea.

    So will it use the Object for TV or VGA (sounds like VGA) - or a new object?

    Is is 1080p or i or lower resolution 720 or less?

    Tim
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Tim, Should have them ready for sale in just a couple more days... I now have the boards, parts, and stencil.
    Well, unless I made a blunder with the PCB, that is...

    I haven't said too much about the driver... Mostly because it's currently in poor shape...
    The SSD1963 only puts out VGA (640x480) or WVGA (widescreen VGA up to 864x480).

    But, you can (in theory) connect Prop pins directly to the TFP410 inputs and use regular VGA output, up to 1600x1200.
    I'm sure 720p is possible this way, and I bet 1080i is too...
    But, this would only be the regular 6-bit color and tile mode, not 24-bit color in graphics mode.
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  • jmgjmg Posts: 11,437
    edited March 2012 Vote Up0Vote Down
    Rayman wrote: »
    The SSD1963 only puts out VGA (640x480) or WVGA (widescreen VGA up to 864x480).
    But, you can (in theory) connect Prop pins directly to the TFP410 inputs and use regular VGA output, up to 1600x1200.

    The difference there, is the SSD1963 has shiploads of RAM, which the Prop does not...

    Can the SSD1963 manage 800x600 and 1024x768, with a reduction in bits per pixel ?
  • RaymanRayman Posts: 8,507
    edited March 2012 Vote Up0Vote Down
    Unfortunately no. At least, not as far as I know.

    Well, you might actually be able to do either of those resolutions with just a 640x480 active area.
    But, it's hard to imagine how that would be useful...
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  • RaymanRayman Posts: 8,507
    edited April 2012 Vote Up0Vote Down
    Just baked a production board last night to see where we stand...

    Had to clean up a few pins with solder wick, but wasn't too bad.
    Important thing is that the board works! So, it's ballistic now. Should have them for sale on the website in just a couple days.
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