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 18:34, 13 February 2020
Contents
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
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
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)
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