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Non Gadgeteer LCD on Fez Raptor - Guidance Needed


#1

Hi guys, I recently purchased a Fez Raptor Dev board, coming from a software background this is my first attempt with working with MCUs, since receiving it I’ve managed to setup all that’s required to get my board communicating successfully with my PC, I’ve made some basic programs to configure some pins as input/outputs etc. Now on to why I’m posting, I recently purchased a 7" LCD from http://www.buydisplay.com/default/7-tft-lcd-touch-screen-display-module-800x480-for-mp4-gps-tablet-pc.html , the descriptions for the FFC cable are as follows:

1 - LEDK - LED Cathode
2 - LEDA - LED Anode
3 - GND - Ground
4 - VDD - Power supply(Digital +3.0V)
5-12 - R0~R7 - Red Data
13-20 - G0~G7 - Green Data
21-28 - B0~B7 - Blue Data
29 - GND - Ground
30 - CLK - Clock
31 - DISP - Disp=“on” when pin 31 is connected with high-level. - Disp=“off” when pin 31 is connected with low-level.
32 - HSYNC - Horizontal sync input in RGB mode. (Short to GND if not used)
33 - VSYNC - Vertical sync input in RGB mode. (Short to GND if not used)
34 - DEN - Data Enable
35 - NC - NC
36 - GND - Ground

Using some breakout board, headers and jumper cables I have hooked everything up as follows:
R Socket - Pins 3-7 to 5-9 of LCD, Pin 8 to 33, Pin 9 to 32
G Socket - Pins 3-8 to 13-18, Pin 9 to Pin 2 (“Not sure about this one”)
B Socket - Pins 3-7 to 21-25, Pin 8 to Pin 34, Pin 9 to Pin 30
Pin 4 of LCD I have connected to a 3.3V supply on Dev Board and all the Ground Pin to a common ground on Dev Board

Ok, so if any of you could provide me with some guidance about what I may be doing right or wrong then that would be great, thanks in advance.


#2

Looks com the pins like the display needs 8 bytes for each color + all the extras. That’s more than you get from the three sockets. I think you would need an adapter/converter in between.

EDIT: 8 bytes -> should be -> 8 bits wide bus


#3

Thanks for the response, surely I would not need to connect all the RGB lines up, what I have would this only limit my choice of colors, also what about the other connections I’ve made, do they look ok?


#4

You can use RGB 565 connections, as you have already done so.

Connecting backlight control, pin 9 on G socket to LEDA may not work. This pin should be use to control shutdown of the LCD backlight power circuit.

Does your LCD module have the backlight circuit ? If not you should first add that using a suitable LCD white LED driver with the required passives.

Without backlight nothing will be visible assuming that everything else is on spec. LCD LED voltage is greater than 3.0v and can go upto 12v or 24v depending on your LCD module.


#5

Hi Rajesh, your question “Does your LCD module have the backlight circuit ?”, I’m not sure, there seems to be a circuit printed onto the FFC cable but as this is all new to me I don’t know what it’s for, you can see a photo here http://www.buydisplay.com/media/catalog/product/cache/1/image/c577d1203d4a53d9f98182eb6081b1d6/7/_/7_inch_800x480_tft_lcd_touch_display_module_for_mp4_gps_tablet_pc.jpg


#6

You will be able to get this display to work but as it is 8 bit for each colour, you’ll need to connect the GHI output to the upper 8 bits and tie the lower unused bits to ground. It’s not ideal but it will work fine if you don’t need accurate colours :slight_smile:

You’ll need to work out the timing for this and write these to the LCD controller. There are samples on the GHI website on how to do this.

As for the LED, as Rajesh points out, you will need a driver for this. The voltage is 22V at 40mA and a suitable step up driver is going to be needed for this to work from 3.3V.

Have a look at the schematic for the 4.3" LCD as it should give you an idea of whats needed to drive this display from the GHI LCD digital outputs.


#7

Hi Dave, thanks for your response, I will try and source a suitable driver for this.


#8

Ok, so regarding the LCD Backlight, going by what you guys have pointed out so far, I’m assuming that something like this item I found on ebay should work “M2577 DC-DC Boost Step-up Adjustable Converter Circuit Board Module 3-30V 4-35v” http://www.ebay.co.uk/itm/LM2577-DC-DC-Boost-Step-up-Adjustable-Converter-Circuit-Board-Module-3-30V-4-35v-/390743148006?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5afa1b45e6


#9

Not really. That does not control the current. LED’s require a constant current supply.

Something like the AP3031 or the NCP5005 is better suited to driving an LED. They have a current feedback circuit that sets the current you want to use. They can also be controlled by PWM for dimming.


#10

Hi Dave, thanks for your suggestions but since my electronics experience is limited I would prefer to purchase something pre-assembled with all the passive components hooked up, looking on ebay again I found this which looks like it could do the job but I can’t be sure.


#11

@ chillydk147 - Were you successful in achieveing a non-gaggateer LCD to a gadgeteer board. I too am trying something of this sort. I am trying it for Fez Hydra board and with a LCD having 40 pins. Please let me know if you have succeeded in this requirement of yours…

Please find the details of the LCD below

This 3.2 inch QVGA TFT LCD Display module has a 65K Color capable LCD with a resolution of 320 x 240 pixels. The module includes Resistive Touch Screen Panel and a Standard SD Card slot. SSD1289 is used to control LCD and the touch panel is controlled by XPT2046.

The module can be interfaced with any MCU like STM32, AVR and 8051 using the 40 pins breakout header that includes SD card and touch panel interface. The module can be driven in 16bit data interface mode.

This LCD Module can be directly plugged into Arduino board using ‘TFT LCD Adapter Shield for Arduino’ shield. The LCD on this module has a has a wide viewing angle and a decent contrast ratio.

Specifications:

Display Type: LCD TFT
Display Size: 3.2 inches - diagonal
Display Resolution: 320 × 240 pixels
Display Colors: 65K Colors
Display Controller: SSD1289
Touch Screen Type: Resistive
Touch Screen Controller: XPT2046
SD Card Type: Standard SD Card Slot with led indicator
SD Card Interface: SPI interface
Blacklight: LED Backlight with hardware or software control
Data Interface: 16 bit interface for microcontrollers
Interface Header: 40 pin Interface
Power Supply: +5V

Pinout details can be found in the snapshot attached. Please let me know if these 40 pins can be interfaced with 40 pins of RGB and T of Fez Hydra board

Thanks,
Prabhu


#12

The display you have is an SPI ‘smart’ display. You can conect it up and control it over the SPI bus, but not with the native parallel RGB+T pins.


#13

The controller actually has RGB interface, but it is not the default one. That means you have to enable it somehow first (I guess you can do it with an SPI interface).

Connection is pretty straightforward. Wire HSYNC, VSYNC, DOTCLK, DEN control signals, and then a bunch of color signals: six wires for red, green and blue part. LCD uses 6 bits for each color, but NETMF support 5-6-5 configuration, so just use the most significant bits, and ground the remaining red and blue bit.

Wiring is easy for those circuits :slight_smile: finding the right registers to configure is not…


#14

Hi Guys, I did indeed manage to interface successfully with my LCD Panel although I needed a little outside help by an engineer on Freelancer.com, below is a link to documentation as well as a sample .NETMF project which shows how to hook it up


#15

@ chillydk147 - good news. Post it on codeshare including a link to the display datasheet and you’ll get some points towards a GHI discount and a nice warm glow.


#16

@ chillydk147 - Can you please share the image of how the 40 pins of LCD u have connected to Gadgeteer board. It will be very helpful for non-harware guys like me to understand the connection you have made if you explain it briefly with diagram.

Thank you


#17

Sorry I dont have any images to share as this was all pulled apart, but I can tell you that the LCD was connected to this breakout board http://www.newhavendisplay.com/nhdffc40-p-1155.html with some header pins soldered on.


#18

@ chillydk147 - But this is only an adapter board for LCD’s but the snapshot attached contains the complete PCB for LCD and touch along with SD card. I just want to know the pin numbers of LCD board to be connected to Fez Hydra board smthing like below

Pin 1 of LCD to Pin — of Fez Hydra

Thank you


#19

Like you I’m not hardware either, the Pin arrangement explained on the last 2 pages of the word doc are for a Fez Raptor, I know nothing about your Dev Board, also note that Pins 1 and 2 of LCD must be connected to a separate Power Supply, these pins are for the LCD Backlight


#20

Also the SD card and Touch panels were optional add-ons which I never chose, only the LCD Panel is interfaced here