Difference between revisions of "VGAX49"

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 +
[[File:tindie-mediums.png|link=https://www.tindie.com/products/land_boards/ps2-keyboardmouse-adapter-pcb-only-ps2x49/]]
 +
 
[[File:VGAX49_P901-cropped-720px.jpg]]
 
[[File:VGAX49_P901-cropped-720px.jpg]]
  
 
== Features ==
 
== Features ==
  
−
* Digital VGA adapter
+
* Analog VGA adapter
−
* 16-bit digital video
+
* Up to 16-bit digital video
−
** 5:6:5 (R:G:B) mapping (maximum)
+
** 5:6:5 (R:G:B) mapping (maximum- 16 bits)
−
** 2:2:2 (R:G:B) mapping (option)
+
** 3:3:2 (R:G:B) mapping (option - 8 bits)
 +
** 2:2:2 (R:G:B) mapping (option - 6 bits)
 +
** 1:2:1 (R:G:B) mapping (option - 4 bits)
 
* Uses summing resistors
 
* Uses summing resistors
 
* DB-15F connector
 
* DB-15F connector
Line 17: Line 21:
  
 
=== J1 - Digital Connections ===
 
=== J1 - Digital Connections ===
 +
 +
[[file:VGAX49_J1.PNG]]
 +
 +
* Ex: R0 is the least significant Red bit (connects to 10K resistor)
  
 
=== P1 - VGA connector ===
 
=== P1 - VGA connector ===
Line 35: Line 43:
 
* Too much effort is put into using precision resistors - the human eye is not that picky
 
* Too much effort is put into using precision resistors - the human eye is not that picky
  
−
=== 2:2:2 Resistor Simulation ===
+
== VGA - Ideal Drive 2 bit Case ==
 +
 
 +
* 3.3V driver requires less than 8 mA
 +
** Configure FPGAs output as 3.3V LVTTL and 8mA drive current
 +
* Ideal case drive current
 +
* Full scale video = 0.7V
 +
* VGA Termination resistor = 75 Ohms
 +
** 0.7V into 75 Ohms = 9.33 mA
 +
* R-2R values
 +
** Ideal resistor values are 417.9 ohms and 835.7 ohms
 +
** [http://www.brannonelectronics.com/images/STANDARD%20VALUE.pdf Standard value 1% resistors]
 +
** 1% standard values are:
 +
*** R1 = [https://www.mouser.com/ProductDetail/652-CR0805FX-4220ELF 422 (Mouser)] Ohms
 +
*** R2 = [https://www.mouser.com/ProductDetail/603-RC0805FR-07845RL 845 (Mouser)] Ohms
 +
*** Get closest values
 +
*** 0V, 0.228V, 0.460V, 0.693V
 +
* Voltage steps are:
 +
 
 +
[[File:VGA_Sim_2R_Voltage.PNG]]
  
−
* Assumptions
+
* Current steps are:
−
** 3.3V Drive out of FPGA
 
−
** 8 mA max drive current (typical FPGA drive current)
 
−
* Using common value, 5% resistors
 
−
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA (close enough to max of FPGA)
 
−
** Voltage with 330/75 ohm voltage divider is 0.61V - not full brightness
 
−
* Next standard value from 330 ohms is 680 ohms
 
−
** Voltage is 0.83V - better brightness
 
  
 
[[File:VGA_Sim_2R_Current.PNG]]
 
[[File:VGA_Sim_2R_Current.PNG]]
  
−
[[File:VGA_Sim_2R_Voltage.PNG]]
 
  
−
=== 5:6:5 Resistor Simulation ===
+
== VGA - Ideal Drive 3 bit Case ==
 +
 
 +
* 3.3V driver requires less than 8 mA
 +
** Configure FPGAs output as 3.3V LVTTL and 8mA drive current
 +
* Ideal case drive current
 +
* Full scale video = 0.7V
 +
* VGA Termination resistor = 75 Ohms
 +
** 0.7V into 75 Ohms = 9.33 mA
 +
* R-2R values
 +
** 5% resistor values are 470 ohms, 1K ohms and 2.2K ohms
 +
*** Produces 0.697V
 +
 
 +
[[file:VideoDAC_3bit_Voltage.PNG]]
 +
 
 +
== 5:6:5 Resistor Simulation ==
  
 
* Assumptions
 
* Assumptions
Line 56: Line 88:
 
** 8 mA max drive current (typical FPGA drive current)
 
** 8 mA max drive current (typical FPGA drive current)
 
* Using common value, 5% resistors
 
* Using common value, 5% resistors
−
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA (close enough to max of FPGA)
+
* Model most significant bit resistor as 1/2 the full scale voltage (0.7V) single resistor value
−
** Voltage with 330/75 ohm voltage divider is 0.61V - not full brightness
+
* 75 Ohm terminator in monitor
−
* Next standard value from 330 ohms is 680 ohms
+
* 0.7V at 75 Ohms = 9.33mA
−
** Voltage is 0.83V - better brightness
+
* Series resistor - single resistor value is (3.3V-0.7V)/9.33mA is 278.6 Ohms
−
* Voltage with all 6 resistors (Green case) is 1.07V (full brightness)
+
* First resistor is 2x 278.57 = 557.1 Ohms
 +
* Each resistor is 2x the previous resistor
 
* Simulation uses the same 4 value steps (real case would have 2^5 or 2^6 steps)
 
* Simulation uses the same 4 value steps (real case would have 2^5 or 2^6 steps)
 +
* Voltage steps
  
−
[[File:VGA_Sim_2R_Current_6_res.PNG]]
+
[[File:VideoDAC_6bit_Voltage.PNG]]
−
 
 
−
[[File:VGA_Sim_2R_Voltage_6_res.PNG]]
 
−
 
 
−
=== ESP32 Drive ===
 
−
 
 
−
* The ESP32 drive current is significantly more than an FPGA
 
−
** 40 mA
 
−
** More than enough to drive to 1V (saturation level on VGA).
 
−
* 1V at 75 Ohms is 13.3 mA
 
−
* 2:2:2 270/470 Ohm simulation
 
−
* -10 mA (max)
 
−
* 0.96V (max)
 
−
 
 
−
[[File:VGA_Sim_2R_Current_ESP32.PNG]]
 
−
 
 
−
[[File:VGA_Sim_2R_Voltage_ESP32.PNG]]
 
  
−
=== Ideal Drive 2:2:2 Case ===
+
* Current steps
  
−
* Ideal case drive current
+
[[File:VideoDAC_6bit_Current.PNG]]
−
** 1V, 75 Ohms = 13.33 mA
 
−
** 3.3V driver
 
−
** [http://www.brannonelectronics.com/images/STANDARD%20VALUE.pdf 1% resistors]
 
−
*** Get closest values
 
−
*** R-2R values
 
−
** 2/3 of the drive comes from the smaller resistor
 
−
** Ideal resistor values are 261, 523 ohms
 
−
*** 0V, 0.331V, 0.661V, 0.992 V
 
  
 
== Schematic ==
 
== Schematic ==

Latest revision as of 13:43, 14 July 2022

Tindie-mediums.png

VGAX49 P901-cropped-720px.jpg

Features

  • Analog VGA adapter
  • Up to 16-bit digital video
    • 5:6:5 (R:G:B) mapping (maximum- 16 bits)
    • 3:3:2 (R:G:B) mapping (option - 8 bits)
    • 2:2:2 (R:G:B) mapping (option - 6 bits)
    • 1:2:1 (R:G:B) mapping (option - 4 bits)
  • Uses summing resistors
  • DB-15F connector
  • 49x49mm ODAS form factor
  • Mounting holes

Connectors

VGAX49.PNG

J1 - Digital Connections

VGAX49 J1.PNG

  • Ex: R0 is the least significant Red bit (connects to 10K resistor)

P1 - VGA connector

Simulation

  • Each color is independently driven and can be considered individually
  • Critical design criteria is output voltage and current capability of the driving part
  • Use common value, 5% resistors
  • Each resistor is about 2X the value of the previous resistor
  • 1V is drive level for VGA specification
    • VGA presents a 75 Ohm load
    • 1V at 75 Ohms is 13.3 mA
  • Series resistors present a voltage divider between the resistors on the card and the VGA load
  • The resistor with the smallest resistance value has larger current from the source device pin
  • Current switches from source to sink depending on the voltages on the other resistors
  • Each resistor is 2X the value of the previous resistor
  • Too much effort is put into using precision resistors - the human eye is not that picky

VGA - Ideal Drive 2 bit Case

  • 3.3V driver requires less than 8 mA
    • Configure FPGAs output as 3.3V LVTTL and 8mA drive current
  • Ideal case drive current
  • Full scale video = 0.7V
  • VGA Termination resistor = 75 Ohms
    • 0.7V into 75 Ohms = 9.33 mA
  • R-2R values
  • Voltage steps are:

VGA Sim 2R Voltage.PNG

  • Current steps are:

VGA Sim 2R Current.PNG


VGA - Ideal Drive 3 bit Case

  • 3.3V driver requires less than 8 mA
    • Configure FPGAs output as 3.3V LVTTL and 8mA drive current
  • Ideal case drive current
  • Full scale video = 0.7V
  • VGA Termination resistor = 75 Ohms
    • 0.7V into 75 Ohms = 9.33 mA
  • R-2R values
    • 5% resistor values are 470 ohms, 1K ohms and 2.2K ohms
      • Produces 0.697V

VideoDAC 3bit Voltage.PNG

5:6:5 Resistor Simulation

  • Assumptions
    • 3.3V Drive out of FPGA
    • 8 mA max drive current (typical FPGA drive current)
  • Using common value, 5% resistors
  • Model most significant bit resistor as 1/2 the full scale voltage (0.7V) single resistor value
  • 75 Ohm terminator in monitor
  • 0.7V at 75 Ohms = 9.33mA
  • Series resistor - single resistor value is (3.3V-0.7V)/9.33mA is 278.6 Ohms
  • First resistor is 2x 278.57 = 557.1 Ohms
  • Each resistor is 2x the previous resistor
  • Simulation uses the same 4 value steps (real case would have 2^5 or 2^6 steps)
  • Voltage steps

VideoDAC 6bit Voltage.PNG

  • Current steps

VideoDAC 6bit Current.PNG

Schematic

Assembly Sheet

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