# Difference between revisions of "VGAX49"

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== 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 | ||

− | |||

** 8 mA max drive current (typical FPGA drive current) | ** 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) | |

− | |||

− | |||

− | |||

− | |||

− | |||

− | * 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 | ||

− | |||

* 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 | ||

− | |||

** 8 mA max drive current (typical FPGA drive current) | ** 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) | |

− | |||

− | |||

− | |||

− | |||

− | |||

− | * 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 | ||

− | |||

* 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

## 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

- 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

### 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)

### 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)

### 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