January 30, 2015   Posted by: Dr. Ace Jeangle

How to use HDMI-dualLVDS converter

Our dualLVDS converter has two LVDS channels and supports 24-bits color panels with up to WUXGA (1920×1200 px) resolution. It also has on-board configurable backlight voltage generator and microcontroller with USB interface. We offer this converter as a standalone product, and also in bundle with 10″ WUXGA panel.

DualLVDS converter board has the following connectors:
HDMI-dualLVDS converter

Powering board

Converter board alone takes up to 0.4A current in active mode, with connected 10″ FullHD+ current goes up to 1.2A when backlight is set to maximum value. Board and LCD can be powered either by external power supply (5V at least 2A, jack is OD=2.6mm, ID=0.65mm, positive central pin) or by USB. By default it can be powered by external supply only. For USB power you should install 0R resistor in R12 position. CAUTION! Do not connect external power supply when R12 is installed, it can damage your USB port.

Backlight voltage generator

Converter has on-board configurable backlight voltage generator that can deliver up to 35V/1A. Backlight voltage can be set with R3, R11 resistors (see above picture for formula). We supply boards with default 24V backlight voltage. Take note that R11 should be in 5K – 20K range. If LCD backlight takes more than 3W, then U6 and L1 inductor can have temperature up to 100C degree. In this case you should use additional heat sink to avoid overheating.

LVDS cable

If you buy standalone board, then you will need to make your own LVDS cable for your LCD panel. We supply mate housing connector and 50 pcs of pin terminals together with board, they can be crimped to cable wires with AWG #32 crimp tool. We recommend using PA-09 crimp pliers, it has affordable price and provides high quality results. Below is pinout of LVDS connector, PDF version is available here: dualLVDS board pinout.
dualLVDS Pinout
Pins GPIO_xxx are connected directly to PIC microcontroller and can be used to control different functions of LCD. We ship board with our standard example program (see source code below) that uses pin GPIO_RA5 to turn on LCD backlight when input video signal is detected. If video signal is lost, LCD backlight will be turned off. Also, pin GPIO_RC5 is connected to PIC PWM generator, and can be used to control brightness of LCD backlight.

Update of EDID information

We supply our converter board with pre-loaded EDID data for our 10″ FullHD+ LCD (resolution 1920×1200 px). You will need to update EDID information in converter in order to use it with your own LCD. EDID update procedure is described here: How to program custom EDID data in HDMI converter

Firmware update with USB bootloader

Board is supplied with embedded USB bootloader for easy firmware upload. To update firmware you should start board in bootloader mode by shorting both pins on ambient light sensor connector with jumper, then turn on power. Green LED will light on, and you will have 3 seconds to remove jumper in order to start bootloader. Green LED will blink when bootloader is active. You should follow steps 4 and 5 of this firmware upload procedure: Firmware upload HID USB bootloader is available here: HID USB bootloader. You can use firmware for our FullHD+ LCD bundle for your own LCD projects, latest version of firmware is available here: dualLVDS/FullHD+ firmware

Building PIC firmware

To build own PIC firmware you will need MPLAB.X environment from Microchip with XC8 compiler: MPLAB X, XC8 compiler.
Bootloader occupies the program memory region 0x000-0x903. The application firmware is supposed to occupy the 0x904-[end of flash] region of program memory.
Here are two linker setting changes that are required for the application project:

  1. Under the build configuration–>XC8 global options–>XC8 linker–>Option categories:Additional options the “Codeoffset” must be set to: 0x904
  2. Under the build configuration–>XC8 global options–>XC8 linker–>Option categories:Memory model, the “ROM ranges” must be set to: default,-0-903

In addition to the above, make certain that all configuration bit settings between the bootloader firmware project, and the application firmware project, match 100% exactly, see our example firmware for details:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
#include "typedefs.h"

__CONFIG(FOSC_INTOSC & WDTE_OFF & PWRTE_ON & MCLRE_OFF & CP_OFF & BOREN_ON & CLKOUTEN_OFF & IESO_OFF & FCMEN_OFF);
__CONFIG(WRT_OFF & CPUDIV_NOCLKDIV & USBLSCLK_48MHz & PLLMULT_3x & PLLEN_ENABLED & STVREN_ON &  BORV_LO & LPBOR_OFF & LVP_OFF);

#define _XTAL_FREQ 48000000                     // Frequency of crystal (INTOSC in our case)

void main(void) {
    OSCCON = 0xFC;                              // 3x PLL enabled from 16MHz HFINTOSC
    ACTCON = 0x90;                              // Enable active clock tuning from USB
    while(OSCSTATbits.PLLRDY == 0);             // Wait for PLL ready/locked

    ANSELAbits.ANSA4=0; TRISAbits.TRISA4=1;     // Define SCDT In pin (input)
    LATAbits.LATA5=0; TRISAbits.TRISA5=0;       // Define SCDT Out pin (output, default to 0)
    LATCbits.LATC5=0; TRISCbits.TRISC5=0;       // Define PWM pin (output, default to 0)
    LATCbits.LATC3=1; TRISCbits.TRISC3=0;       // Define LED pin (output, default to 1 - LED Off)

    while(1) {
        // If video signal is detected
        if (PORTAbits.RA4) {                    
            LATAbits.LATA5=1;                   // Enable video outputs
            LATCbits.LATC5=1;                   // Enable backlight (PWM=1 - max. brightness)
            LATCbits.LATC3=0;                   // Turn LED On
        }
        // If video signal is lost
        else {
            LATAbits.LATA5=0;                   // Disable video outputs
            LATCbits.LATC5=0;                   // Disable backlight (PWM=0 - turn off backlight)
            LATCbits.LATC3=1;                   // Turn LED Off
        }
    }
}

Ambient light sensor and backlight brightness

Ambient light sensor is available as an option, and can measure ambient light level for automatic backlight control.
ambient light sensor
Ambient light sensor should be connected to connector J1, red color wire to pin 1 on connector. Light level is available as a voltage in range 0 (dark) to 2.5V (max. light) on pin RC2 (ADC channel 6) of PIC microcontroller. Backlight brightness can be controlled with help of PWM signal on GPIO_RC5. Additional information about backlight control through USB HID commands is available in this how-to: How to control LCD backlight (USB HID)

Board schematic

Board schematic is available here: http://goo.gl/NSWTIQ

See in action

Video with dualLVDS converter board and our FullHD+ LCD is available here: FullHD+ LCD with HDMI dualLVDS converter

Follow us on Twitter to get instant notification about new firmware release:

2 comments posted in: blog   |   How-To
2 comments
  1. yong jun, jung
    Jul 31, 2016

    Can you set the backlight voltage of dual LVDS converter with 12V?
    If there was a way, let me know how.

    • Dr. Ace Jeangle
      Jul 31, 2016

      Yes, you can, read carefully “Backlight voltage generator” part of this How-to.

Leave a Reply

Your email address will not be published. Required fields are marked *

Time limit is exhausted. Please reload CAPTCHA.