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Wiring up this VGA & PS2 connector to the propeller - This module seems to have extra pins? — Parallax Forums

Wiring up this VGA & PS2 connector to the propeller - This module seems to have extra pins?

MahonroyMahonroy Posts: 175
in Propeller 1
Hey guys,
I wired up the VGA port from Parallax store and it works great, here it is for reference:
https://www.parallax.com/product/28076

I am now attempting to wire up another module I have, here it is for reference:
http://www.ebay.com/itm/251031101624?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

The Parallax module has R0, R1, G0, G1, B0, B1 (2 pins per color). This new module has R, R0, R1, R2 (4 pins per color? I'm confused).
Do I just wire this up with the R0 & R1, and leave the R & R2 disconnected? Thanks and any help is greatly appreciated!

Comments

  • TubularTubular Posts: 4,702
    edited 2016-02-16 00:51
    Probably use R2 (MSB) and R1, and connect R0 to ground. I think R probably just connects directly to the pin, but check this with a multimeter. Its not clear what resistance values they use

    Similar for green and blue channels

    If using keyboard/mouse, you'll probably need to add the 4 resistors for keyboard/mouse signals (as done on the demo board/proto board etc)
  • MahonroyMahonroy Posts: 175
    edited 2016-02-16 15:51
    Tubular wrote: »
    Probably use R2 (MSB) and R1, and connect R0 to ground. I think R probably just connects directly to the pin, but check this with a multimeter. Its not clear what resistance values they use

    Similar for green and blue channels

    If using keyboard/mouse, you'll probably need to add the 4 resistors for keyboard/mouse signals (as done on the demo board/proto board etc)

    So are you saying I should connect the old R0 to R1, and the old R1 to R2?
    What about the pins that are just labeled R, G, B?

    Here is an image for reference:
    s-l500.jpg
  • PublisonPublison Posts: 12,366
    edited 2016-02-16 16:03
    Ask them for a schematic.

    It would be nice if they had a schematic available, as suggested by their ebay site that says :
    Related ....resource

    That leads nowhere.
  • MahonroyMahonroy Posts: 175
    edited 2016-02-16 16:48
    Publison wrote: »
    Ask them for a schematic.

    It would be nice if they had a schematic available, as suggested by their ebay site that says :
    Related ....resource

    That leads nowhere.

    After searching around I was able to find the schematic:
    http://www.waveshare.com/w/upload/7/7a/VGA-PS2-Board-Schematic.pdf

    So it looks like the 0, 1, 2's are just the resistance value used for each color channel (sorry I am still new to how this VGA stuff works). So I am assuming I would use the 500ohm channel, and the 1k ohm channel? Which one is which on the parallax vga? Since the VGA drivers have the wiring going in a certain order this is something I need to figure out.

    Thanks again for the advice!
  • PublisonPublison Posts: 12,366
    Based on the Parallax Demo Board Schematic,

    https://www.parallax.com/sites/default/files/downloads/32100-Propeller-Demo-Board-Schematic-RevG_0.pdf

    It does not look like you can hit the two resistances needed, 240 ohm and 470 ohm.

    You could always replace the resistors, but why bother when there is a product that does that?



  • MahonroyMahonroy Posts: 175
    Publison wrote: »
    Based on the Parallax Demo Board Schematic,

    https://www.parallax.com/sites/default/files/downloads/32100-Propeller-Demo-Board-Schematic-RevG_0.pdf

    It does not look like you can hit the two resistances needed, 240 ohm and 470 ohm.

    You could always replace the resistors, but why bother when there is a product that does that?



    Does it matter if the resistances are that exact? What role do these play in the VGA?
  • PublisonPublison Posts: 12,366
    Mahonroy wrote: »
    Publison wrote: »
    Based on the Parallax Demo Board Schematic,

    https://www.parallax.com/sites/default/files/downloads/32100-Propeller-Demo-Board-Schematic-RevG_0.pdf

    It does not look like you can hit the two resistances needed, 240 ohm and 470 ohm.

    You could always replace the resistors, but why bother when there is a product that does that?

    https://www.parallax.com/product/28076



    Does it matter if the resistances are that exact? What role do these play in the VGA?

    470 ohm needed on R2. The R2 input is at 500 ohms, (1K parallel 1K), but neither of the R1 or R2 are close to the needed 240 ohm. And yes they have to be close.


  • MahonroyMahonroy Posts: 175
    Publison wrote: »
    Mahonroy wrote: »
    Publison wrote: »
    Based on the Parallax Demo Board Schematic,

    https://www.parallax.com/sites/default/files/downloads/32100-Propeller-Demo-Board-Schematic-RevG_0.pdf

    It does not look like you can hit the two resistances needed, 240 ohm and 470 ohm.

    You could always replace the resistors, but why bother when there is a product that does that?

    https://www.parallax.com/product/28076



    Does it matter if the resistances are that exact? What role do these play in the VGA?

    470 ohm needed on R2. The R2 input is at 500 ohms, (1K parallel 1K), but neither of the R1 or R2 are close to the needed 240 ohm. And yes they have to be close.


    What role does this play here? Why is there a choice? I don't understand why all VGA modules wouldn't operate the same way? I can certainly add some resistors to make the 240 ohm and 470 ohm, but why was this designed this way if its not correct?
  • Cluso99Cluso99 Posts: 18,069
    What you have is a VGA designed to have 3 inputs per color, using the R2R divider method (500R, 1K, 2K) with a 75R//150pF termination.

    With wrong values you will just get wrong colors.
    The 75R termination is quite low. Usually the prop ignores this termination. A value of 130R would be better.

    But hey, give it a go and you will see the colors. Then when you change the values you will see the differences.
  • AribaAriba Posts: 2,690
    Connect the R1 output to the R2 and the R0 input, and the R0 output to R1 input of the VGA board. Same for G and B.
    The resistors are a bit high and the 75 Ohm resistor will make the signal quite low, so the colors will be darker then usually. But this can be corrected by adjusting the Brightness on the monitor.

    The Demoboard resistors are too low and give a saturated output (as Phil showed us) - this can not be corrected with brightness control.

    As Tubular said: You will need Pullup resistors for the PS2 lines, the Propeller has them not built in. (4k7.. 10k)

    Andy

  • TubularTubular Posts: 4,702
    Mahonroy do you already have the module? If so can you measure the resistances with a multimeter please?

    I don't think the schematic matches the picture, there's a different number of passives for a start, so no reason the resistor values are likely to be correct either.

    As Andy said it will probably work but be quite dark. About half brightness (383mv rather than 700mv peak), assuming the monitor is also terminated with 75 ohms. And that is with R2 and R0 connected together on the module to boost the brightness a little bit (it'd be 328mv peak without)
  • PublisonPublison Posts: 12,366
    Why are we trying to fix a cheap ebay module when Parallax, (who host these forums), has one that works? :)

    https://www.parallax.com/product/28076


  • TubularTubular Posts: 4,702
    edited 2016-02-17 02:42
    Its an experiment, Jim.

    We're repeating the classic experiment in false economy, using a different product, to see whether anything's changed.

    So far results are trending as per previous experiments by countless others, but we're only ~30 hours in...

  • MahonroyMahonroy Posts: 175
    edited 2016-02-18 20:30
    Ariba wrote: »
    Connect the R1 output to the R2 and the R0 input, and the R0 output to R1 input of the VGA board. Same for G and B.
    The resistors are a bit high and the 75 Ohm resistor will make the signal quite low, so the colors will be darker then usually. But this can be corrected by adjusting the Brightness on the monitor.

    The Demoboard resistors are too low and give a saturated output (as Phil showed us) - this can not be corrected with brightness control.

    As Tubular said: You will need Pullup resistors for the PS2 lines, the Propeller has them not built in. (4k7.. 10k)

    Andy

    Thanks! I will give this a try and see how it works out.
    Tubular wrote: »
    Mahonroy do you already have the module? If so can you measure the resistances with a multimeter please?

    I don't think the schematic matches the picture, there's a different number of passives for a start, so no reason the resistor values are likely to be correct either.

    As Andy said it will probably work but be quite dark. About half brightness (383mv rather than 700mv peak), assuming the monitor is also terminated with 75 ohms. And that is with R2 and R0 connected together on the module to boost the brightness a little bit (it'd be 328mv peak without)

    I do have one of these modules here with me.

    Ok I measured the resistance and its correct. R2 is 646 ohms, R1is 1.142 Kohms, R0 is 2.116 Kohms. This is the same for Green and Blue as well.
    Publison wrote: »
    Why are we trying to fix a cheap ebay module when Parallax, (who host these forums), has one that works? :)

    https://www.parallax.com/product/28076

    I already have that parallax VGA module here and it works.

    I needed a VGA module with a single PS/2 connector on it so this one I found online seemed to be a good candidate for projects.
  • MahonroyMahonroy Posts: 175
    edited 2016-02-18 22:45
    Ariba wrote: »
    Connect the R1 output to the R2 and the R0 input, and the R0 output to R1 input of the VGA board. Same for G and B.
    The resistors are a bit high and the 75 Ohm resistor will make the signal quite low, so the colors will be darker then usually. But this can be corrected by adjusting the Brightness on the monitor.

    The Demoboard resistors are too low and give a saturated output (as Phil showed us) - this can not be corrected with brightness control.

    As Tubular said: You will need Pullup resistors for the PS2 lines, the Propeller has them not built in. (4k7.. 10k)

    Andy

    I did this and it works, thanks a lot!

    I see what you guys mean about it being a bit on the dim side. I turned the brightness all the way up and its good enough.

    Instead of connecting the R0 to R1 input on the VGA board like you suggested... can I instead connect R0 to R0 and R1 on the VGA? (and still have R1 output to the R2 and R0 input of the VGA board). This would give me 333 ohms for the R1, and 666 ohms for the R0 which would be better right?

    EDIT:
    Ok I just realized that it wouldn't work because everything will get parallel with each other. So in this case the only alternative would be to add an aditional 1K resistor ontop (parallel) of the R1 input on the VGA board and that would be pretty close?
  • TubularTubular Posts: 4,702
    Good that you got it working

    Does your board have the 75 ohms to ground on it, that was shown on the schematic? Or does it just let the 75 ohm termination in the monitor do the job?
  • TubularTubular Posts: 4,702
    edited 2016-02-18 23:17
    here's the best I think you can do (red ch only shown) 
    Prop Output R1 MSB >-- 28R internal --- 390R external --- (R  input on board) ------------+--> to 75R monitor
Prop Output R0 LSB >-- 28R internal ----160R external --- (R2 input on board) --- 646R ---|
no connect                                                                    --- 1142 ---|
no connect                                                                    --- 2116 ---^

    This gives you 0.7v out peak, assuming 75 ohm termination in the monitors
    the 28 ohms are internal to the prop (the pin driving resistance of the fets). Shown for completeness.
    Note the 240 and 470 ohm resistors often shown on prop circuits result in a saturated result on the top two levels
  • MahonroyMahonroy Posts: 175
    Tubular wrote: »
    Good that you got it working

    Does your board have the 75 ohms to ground on it, that was shown on the schematic? Or does it just let the 75 ohm termination in the monitor do the job?

    Ah, it turns out the VGA module does not have this 75 ohm to ground as shown in the schematic (or those capacitors for that matter).

    Tubular wrote: »
    here's the best I think you can do (red ch only shown) 
    Prop Output R1 MSB >-- 28R internal --- 390R external --- (R  input on board) ------------+--> to 75R monitor
Prop Output R0 LSB >-- 28R internal ----160R external --- (R2 input on board) --- 646R ---|
no connect                                                                    --- 1142 ---|
no connect                                                                    --- 2116 ---^

    This gives you 0.7v out peak, assuming 75 ohm termination in the monitors
    the 28 ohms are internal to the prop (the pin driving resistance of the fets). Shown for completeness.
    Note the 240 and 470 ohm resistors often shown on prop circuits result in a saturated result on the top two levels

    I see, I will give this a shot, thanks again!
  • AribaAriba Posts: 2,690
    Or just locate the 75 Ohm resistors and remove them on the board. They are already in the monitor. This will make it much brighter.

    Andy
  • MahonroyMahonroy Posts: 175
    Tubular wrote: »
    here's the best I think you can do (red ch only shown) 
    Prop Output R1 MSB >-- 28R internal --- 390R external --- (R  input on board) ------------+--> to 75R monitor
Prop Output R0 LSB >-- 28R internal ----160R external --- (R2 input on board) --- 646R ---|
no connect                                                                    --- 1142 ---|
no connect                                                                    --- 2116 ---^

    This gives you 0.7v out peak, assuming 75 ohm termination in the monitors
    the 28 ohms are internal to the prop (the pin driving resistance of the fets). Shown for completeness.
    Note the 240 and 470 ohm resistors often shown on prop circuits result in a saturated result on the top two levels

    I did this and it works great... definitely a lot brighter now, thanks again for the help!
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