Difference between revisions of "VGAX49"
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* 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 | ||
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| + | [[File:VGA_Sim_2R_Current_ESP32.PNG]] | ||
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| + | [[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
