Difference between revisions of "VGAX49"

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=== 2:2:2 Resistor Simulation ===
 
=== 2:2:2 Resistor Simulation ===
  
* 3.3V Drive out of FPGA
+
* Assumptions
* 1V is drive level for VGA specification
+
** 3.3V Drive out of FPGA
* 8 mA max drive current
+
** 1V is drive level for VGA specification
 +
** 8 mA max drive current (typical FPGA drive current)
 
* VGA presents a 75 Ohm load
 
* VGA presents a 75 Ohm load
 
* Series resistors present a voltage divider between the resistors on the card and the VGA load
 
* Series resistors present a voltage divider between the resistors on the card and the VGA load
Line 46: Line 47:
 
=== 5:6:5 Resistor Simulation ===
 
=== 5:6:5 Resistor Simulation ===
  
* 3.3V Drive out of FPGA
+
* Assumptions
* 1V is drive level for VGA specification
+
** 3.3V Drive out of FPGA
* 8 mA max drive current
+
** 1V is drive level for VGA specification
 +
** 8 mA max drive current (typical FPGA drive current)
 
* VGA presents a 75 Ohm load
 
* VGA presents a 75 Ohm load
 
* Series resistors present a voltage divider between the resistors on the card and the VGA load
 
* Series resistors present a voltage divider between the resistors on the card and the VGA load
Line 58: Line 60:
 
* 330 Ohm series resistor into a 75 Ohm load is 8.15 mA
 
* 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
 +
** Voltage is 0.83V - better brightness
 +
* Voltage with all 6 resistors (Green case) is 1.07V (full brightness)
  
 
[[File:VGA_Sim_2R_Current_6_res.PNG]]
 
[[File:VGA_Sim_2R_Current_6_res.PNG]]
  
 
[[File:VGA_Sim_2R_Voltage_6_res.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
 +
 +
[[File:VGA_Sim_2R_Current_ESP32.PNG]]
 +
 +
[[File:VGA_Sim_2R_Voltage_ESP32.PNG]]
  
 
== Schematic ==
 
== Schematic ==

Revision as of 10:34, 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

2:2:2 Resistor Simulation

  • Assumptions
    • 3.3V Drive out of FPGA
    • 1V is drive level for VGA specification
    • 8 mA max drive current (typical FPGA drive current)
  • VGA presents a 75 Ohm load
  • Series resistors present a voltage divider between the resistors on the card and the VGA load
  • 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
  • Each resistor is 2X the value of the previous resistor
  • 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
    • 1V is drive level for VGA specification
    • 8 mA max drive current (typical FPGA drive current)
  • VGA presents a 75 Ohm load
  • Series resistors present a voltage divider between the resistors on the card and the VGA load
  • 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
  • Each resistor is 2X the value of the previous resistor
  • 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)

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

VGA Sim 2R Current ESP32.PNG

VGA Sim 2R Voltage ESP32.PNG

Schematic

Assembly Sheet