Difference between revisions of "VGAX49"

From Land Boards Wiki
Jump to navigation Jump to search
(7 intermediate revisions by the same user not shown)
Line 21: Line 21:
  
 
== Simulation ==
 
== 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
  
 
=== 2:2:2 Resistor Simulation ===
 
=== 2:2:2 Resistor Simulation ===
Line 26: Line 39:
 
* Assumptions
 
* Assumptions
 
** 3.3V Drive out of FPGA
 
** 3.3V Drive out of FPGA
** 1V is drive level for VGA specification
 
 
** 8 mA max drive current (typical FPGA drive current)
 
** 8 mA max drive current (typical FPGA drive current)
* VGA presents a 75 Ohm load
+
* Using common value, 5% resistors
* Series resistors present a voltage divider between the resistors on the card and the VGA load
+
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA (close enough to max of FPGA)
* 1V at 75 Ohms is 13.3 mA
 
* Each color is independently driven
 
* The resistor with the smallest resistance value has larger current from the FPGA pin
 
* Current switches from source to sink depending on the voltages on the other resistors
 
* Use common value, 1% resistors
 
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA
 
 
** Voltage with 330/75 ohm voltage divider is 0.61V - not full brightness
 
** Voltage with 330/75 ohm voltage divider is 0.61V - not full brightness
* Each resistor is 2X the value of the previous resistor
 
 
* Next standard value from 330 ohms is 680 ohms
 
* Next standard value from 330 ohms is 680 ohms
 
** Voltage is 0.83V - better brightness
 
** Voltage is 0.83V - better brightness
Line 49: Line 54:
 
* Assumptions
 
* Assumptions
 
** 3.3V Drive out of FPGA
 
** 3.3V Drive out of FPGA
** 1V is drive level for VGA specification
 
 
** 8 mA max drive current (typical FPGA drive current)
 
** 8 mA max drive current (typical FPGA drive current)
* VGA presents a 75 Ohm load
+
* Using common value, 5% resistors
* Series resistors present a voltage divider between the resistors on the card and the VGA load
+
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA (close enough to max of FPGA)
* 1V at 75 Ohms is 13.3 mA
 
* Each color is independently driven
 
* The resistor with the smallest resistance value has larger current from the FPGA pin
 
* Current switches from source to sink depending on the voltages on the other resistors
 
* Use common value, 1% resistors
 
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA
 
 
** Voltage with 330/75 ohm voltage divider is 0.61V - not full brightness
 
** Voltage with 330/75 ohm voltage divider is 0.61V - not full brightness
* Each resistor is 2X the value of the previous resistor
 
 
* Next standard value from 330 ohms is 680 ohms
 
* Next standard value from 330 ohms is 680 ohms
 
** Voltage is 0.83V - better brightness
 
** Voltage is 0.83V - better brightness
 
* Voltage with all 6 resistors (Green case) is 1.07V (full brightness)
 
* Voltage with all 6 resistors (Green case) is 1.07V (full brightness)
 +
* Simulation uses the same 4 value steps (real case would have 2^5 or 2^6 steps)
  
 
[[File:VGA_Sim_2R_Current_6_res.PNG]]
 
[[File:VGA_Sim_2R_Current_6_res.PNG]]
Line 76: Line 74:
 
* 1V at 75 Ohms is 13.3 mA
 
* 1V at 75 Ohms is 13.3 mA
 
* 2:2:2 270/470 Ohm simulation
 
* 2:2:2 270/470 Ohm simulation
 +
* -10 mA (max)
 +
* 0.96V (max)
  
 
[[File:VGA_Sim_2R_Current_ESP32.PNG]]
 
[[File:VGA_Sim_2R_Current_ESP32.PNG]]
  
 
[[File:VGA_Sim_2R_Voltage_ESP32.PNG]]
 
[[File:VGA_Sim_2R_Voltage_ESP32.PNG]]
 +
 +
=== Ideal Drive 2:2:2 Case ===
 +
 +
* Ideal case drive current
 +
** 1V, 75 Ohms = 13.33 mA
 +
** 3.3V driver which can drive more than 10 mA
 +
** [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
 +
 +
[[File:VGA_Sim_2R_Voltage_ESP32-IdealRes.PNG]]
  
 
== Schematic ==
 
== Schematic ==

Revision as of 11:10, 13 February 2020

VGAX49 P901-cropped-720px.jpg

Features

  • Digital VGA adapter
  • 16-bit digital video
    • 5:6:5 (R:G:B) mapping (maximum)
    • 2:2:2 (R:G:B) mapping (option)
  • Uses summing resistors
  • DB-15F connector
  • 49x49mm ODAS form factor
  • Mounting holes

Connectors

VGAX49.PNG

J1 - Digital Connections

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

2:2:2 Resistor Simulation

  • Assumptions
    • 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

VGA Sim 2R Current.PNG

VGA Sim 2R 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
  • 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
  • Voltage with all 6 resistors (Green case) is 1.07V (full brightness)
  • Simulation uses the same 4 value steps (real case would have 2^5 or 2^6 steps)

VGA Sim 2R Current 6 res.PNG

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)

VGA Sim 2R Current ESP32.PNG

VGA Sim 2R Voltage ESP32.PNG

Ideal Drive 2:2:2 Case

  • Ideal case drive current
    • 1V, 75 Ohms = 13.33 mA
    • 3.3V driver which can drive more than 10 mA
    • 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

VGA Sim 2R Voltage ESP32-IdealRes.PNG

Schematic

Assembly Sheet