Better VGA DAC resistors

Comments

• Cluso99 Posts: 18,069

  2011-10-26 10:39 edited 2011-10-26 10:39

  Drac: Don't forget the TV termination resistor to gnd. I would also change the values somewhat (see post #27 - plug values into spreadsheet #25 or #26)
• Phil Pilgrim (PhiPi) Posts: 23,514

  2011-10-26 10:51 edited 2011-10-26 10:51

  I missed the TV connection. Dr_A, your situation is complicated by the fact that you're sharing the TV and VGA connections. This means that the voltage drop across the internal resistance of the Prop pin will derive from current through both circuits, even though you're only using one at a time. That will require a more complex analysis that what we've done here, since there's a codependence between the two circuits.
  
  -Phil
• Toby Seckshund Posts: 2,027

  2011-10-27 01:37 edited 2011-10-27 01:37

  Many moons ago, on a Blade2 copy, I put an eight way resistor in reversed. Instead of getting P24 - 31 with 10K pullups I got a mind bending set of 20K interconnects.
• Dr_Acula Posts: 5,484

  2011-10-27 02:04 edited 2011-10-27 02:04

  Per the spreadsheet results shown in post #24, I'd change your 270's to 240's.

  
  Thanks Phil - have made the changes.
  
  Re the TV vs VGA, the *best* solution is to solder up one board for TV and another for VGA. With Gadget Gangster boards you can swap those in and out easily.
  
  Keep up the good work!
• Toby Seckshund Posts: 2,027

  2011-10-27 06:46 edited 2011-10-27 06:46

  I seriously doubt that the vast magority of VGA cables have the characteristic impedance of 75 Ohms. They often just have "thin" co-axes or even single wires within an overall shield.
  
  Still it is good to get as close as possible.
• Cluso99 Posts: 18,069

  2011-10-27 14:24 edited 2011-10-27 14:24

  Since Phil has done all the hard work here, may as well use the correct values. There is little cost in this.
  I just plug in VGA or TV modules into my baseboard - its easy as.
• Sapieha Posts: 2,964

  2011-10-29 04:35 edited 2011-10-29 04:35

  Sorry if it is of topic.
  
  BUT for any that need correct pin definitions and theirs Voltages on VGA.
  
  Look on attached picture
  
  

  

  

  

  VGA Connector Signals.jpg

  1006 x 616 - 57K

  VGA Connector Signals.jpg 56.7K
• Oldbitcollector (Jeff) Posts: 8,091

  2012-06-12 18:54 edited 2012-06-12 18:54

  @Phil,
  
  Implemented your OP fix on my test rig tonight. Went from 48 countable colors to 64 colors with the driver I'm using.
  
  My hat's off to you. Nice fix!
  
  OBC