EihiS

May 24, 2013

Raspberry PI : Cheap LCD display MOD

Filed under: Raspberry 3.14 — Tags: , , , , , , , , — admin @ 11:28 am

In this article, i’m going to explain how to connect a raspberry Pi to a cheap LCD display taken from a broken or old DVD player.

The output of the RasPI (video-composite output) is used to send video datas to the LCD panel, and one must configure the /boot/config.txt file of raspbian linux to set the correct width and height for the LCD panel.

This ‘MOD’ for Pi can be applied to many cheap LCD panels one can found into broken or unused DVD players around there : ebay, trash containers and so on.

For my specific case, i had a PROline DVD player , model DVDP650W.it has a video-in jack plug. that’s why i figured out that it should be possible to make it become a kind of mini- tv monitor, by extracting only the video decoding and driving parts.

Once opened, you will find many parts (dont be offraid by that, we are going to clean up that..)
The main board can be removed. The mechanical DVD reader head also. Carefully unpluggin the internal connectors, and removing all blocking screws around ther, you should end up with a kit of PCBs wich are :

The main PCB assembly : Not used

The main PCB assembly : Not used

Notice the input power jacks : 12V . that’s what we will have to power the LCD driver board with. AC/DC adapter directly plugged to the LCD driver board. Tha PCB assembly can be put away - not needed anymore.

This is the LCD driver BOARD. carefully remove the cables going to the LCD panel ( the connector is unlocked by pulling up the greyish/maroon plastic part)

This is the LCD driver BOARD. carefully remove the cables going to the LCD panel ( the connector is unlocked by pulling up the greyish/maroon plastic part)

We need that part, obviously. we also need the CCFL inverter board and the LCD panel itself :

LCD panel model PW065XS4

LCD panel model PW065XS4

The LCD panel’s datasheet is HERE

Now, we just need to reassemble all parts into something looking usable . i’ve used a plastic panel quickly drilled to let the LCD’s flat outlet and CCFL wires going from the front face to the backface where i have fixed the PCBs needed.

SO, ending up with something like that :

Front

Back

Back

You can check all the parts you need :

- the CCFL inverter (top left of the picture) , connected to the LCD driver board

- the 2 potentiometer ’satellite’ pcbs : one for brightness, the other for colour adjustment, connected to the board

- the LCD panel’s flat outlet re-plugged onto the LCD driver board.

Now, for that particular LCD driver board, here is the PINOUT :

LCD driver board power and signal connector

LCD driver board power and signal connector

From left to right, :

1 - LCD on/off.  if let open , LCD is ON. if you put this pin to ground, you’ll put it OFF (CCFL backlight off )
2- Videocomposite GROUND
3-Videocomposite-IN SIGNAL
4-Main GROUND
5-POWER INPUT (+12V)

pin 2 can be tied to pin 5.
I recommend re-using the old cable (6 wires) and solder you wires on it, so you can plug/unplug freely that input part to the PCB assembly.
For the videocomposite signal, just iron a RCA plug (the yellow ones) on it, to be able to connect it to the Raspberry PI’s videocomposite output.

Once done, and once Raspbian linux /boot/config.txt file has been update with the parameters that fit this LCD display, you’ll be able to avec something like that on your homemade mini LCD display :

RaspBian boot done ..

RaspBian boot done ..

And see LXDE’s look :

What a big screen ! :-P

What a big screen ! :-P

Before you end up with that, edit the /boot/config.txt file  and ensure to have this parameters in it :

#lcd panel is 1200×234, but 1200 is for RGB so real size in pixels is 1200/3

framebuffer_width=400

framebuffer_height=200

# values found by trying many. looks the best to avoid flickerings

overscan_left=2

overscan_right=-6

overscan_top=-18

overscan_bottom=-15

sdtv_mode=2    # sets videocomposite output to PAL signal

sdtv_aspect=3    # sets video_composite output to 16:9 format

If anything was going bad ( screen becomes unreadable) , the best is to learn how to use SSH to edit/save and reboot the Pi from a distant computer before applying and testing the display. (take a look at BitVise free SSH software )

Have a nice moding, guys.

stay tuned.

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December 14, 2012

Videopac C-52 : The SCART way ( R.G.B peritel Mod )

Filed under: Hobby Electronics — Tags: , , , , , , , , , , , — admin @ 4:39 pm

Inside the videopac c-52 ( bottom cover removed ) :

The VHF modulator is the board at the bottom of the picture.
It has to be replaced with a little electronic board, to convert the signals incoming from the main cpu ( the one at the center).

The RGB adapter board takes Red, Green, Blue , Composite synchronisation, Luminance, and BF (audio) signals from the CPU.

  • The composite sync signal has to be inverted before it can be sent to the TV set thru the scart (peritel) plug. To do so, we pick up the Vertical and Horizontal Sync signals on the pcb (they are allready inverted at that particular points) then use a classic diode based OR gate.
  • R,G,B and sound signals have to be lowered before getting into the scart.
  • RGB signals, also, have to be mixed with the luminance signal, to get the correct RGB levels at the peritel’s intputs (in the right proportions ).Depending on the combination of said color signal added to the luminance signal , the RGB output voltage will have the following values : 0mv, 200mv, 400mv , 600 mv (approximatively)
  • The RGB signals have to be blanked during the Horizontal blank and Vertical Blank time.
    That point is important ::
    The front porch/back porch for lines is necessary. If the RGB signal is not correctly blanked, the TV set will not show permanently coloured lines ( for example, a blue background of a game ).
  • Pin 8 of the scart can be left ‘floating’, but if you want your TV set to automaticaly switch to the scart, you ‘ll have to put a 12V to that pin. (Unfortunatly, it’s not present at the pins on the edge of the CPU board. Only 5V is available there.) So you will have to turn your TV to ’scart’ mode manually with the remote, or add a diode-pump doubler electronic assembly ( for example you could use the line sync as the working clock for it …)
  • Pin 16 of the scart must be set to the correct voltage to switch the TV to RGB input instead of Composite Video input .
    If  pin 16 is driven between 1 and 3V , the TV set will switch to RGB input. (good )
    If pin 16 is lower than 1V , the TV set will switch to Composite Video Input (bad)
    ->> We have 5V coming from the videopac’s CPU board, then a simple Resistor bridge will be sufficient to lower that input voltage to ~3V .
  • For the audio part, a resistor bridge (divider) is enough to lower the level of the Audio coming from the CPU board then feed it into pins 2 and 6 of the SCART plug ( left + right will play the same MONO signal coming from the videopac ), while pin4 (audio ground) can be joined to the other ground pins.

All scart’s pin name terminated with ‘ground’ can be joined to a common ground, connected to the ground of the Videopac’s CPU board , allthough in about all TV sets, that pins are tied together inside the TV, at pcb level.

Now, here is the schematic  of the C-52’s CPU board, viewed from solder side (bottom cover removed).
I have added important signal’s names for the CPU on this figure.

Now, for information, the SCART plug pinout ( VGA pinout here for comparison ) ( french named PERITEL )

The RGB adapter can be built on a prototype PCB. that’s what i did to create a correct electronic adapter from scratch. Here is how mine looks : (yes, it looks ugly with some components out, but that was a prototype, remember ! )

That module fits in to the bottom left of the videopac, right in place of the removed uhf modulator :


And finally, the result you get : the RGB adapter @ work . (the moire is not visible, actually. it’s just a photo shoot artefact ). The Colours are vivid and fine ! let’s play…


Following a request , here is the .PDF file of the schematic :
Hope this will help you into moding the Videopac: rgb_videopac_c52_adapter-78v (pdf)

  • Notice : IC4 ( U4:A on the schematic ) , on my pcb version, was replaced by a 2 x 1n4148 diodes based OR gate, so the final circuit has only 2 TTL IC on it, and VSYNC/HSYNC signals are taken from IC669 instead of IC652 , as you can see on the picture of the cpu’s bottom pcb.
  • Also, IC652-pin27’s connection (sound) is directly available at P6-3, as you may have noticed.
Finally, here is a partial schematic , extracted from the JET25 service manual. the pcb/IC , as i can judge, is similar to the one on the C-52.It may help you understanding the how-why of the SCART adapter described on this website.

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