Displaying an image on a video screen

[Michael Lew]

Going a bit deeper on my Facebook post of yesterday, which I quote here :
> Wondering if anyone has experience connecting a small LCD screen
> to the Raspberry Pi. I saw Adafruit sells some ; but I found here in Tel-Aviv
> a Chinese product (brand : EastRising ; model : ER-TFTM070-4 ; version 2.1).
> Any hint on how to actually connect / make this screen work with the Raspberry Pi
> (model B+) would be appreciated...!

The model of the raspberry Pi that I use (B+) has a digital video output (HDMI),

in contrast to an early model which only had an analog video output (RCA).

The LCD screen is basically just a two-dimensional matrix of pixels. How is

the addressing done exactly, I don't know. But basically you need to give a

value of (R,G,B) for each pixel, n times per second, where n is the refresh

frequency that you want. Typically n needs to be larger than 15 Hz to give

the illusion of cinematic movement... It's 24 Hz for old-fashioned cinema.

Taking into account the persistence of vision, there is an issue with frame

buffers, as always, but we would need a high frame-rate camera to really

investigate what is happening at the pixel level with a screen in terms of :

- the order in which pixels are scanned (such as interlacing in old TVs)

- the duration that a pixel will remain "on" with a specific color, once it

has been sent that specific value, and how it decays (if it does) - does

it consume energy to remain "on" or not.

- controlling the intensity of the back light LCD

The easiest solution with the Raspberry Pi is probably to get a display that

accepts directly either RCA or HDMI, but since I found this Chinese product,

I guess we need to learn how to use it here at TAMI, because it's more

low-level.

Basically I found that this screen uses a controller chip called the SSD1963,

designed by a respectable company in Hong Kong called «Solomon Systech».

This chip takes care among others of this frame buffer problem.

The chip accepts a clock signal, and has the ability to receive in parallel

24 bits of data (on 24 separate input pins labeled DB0, DB1... until DB23),

but can be used also in 8/9/16/18 bit mode.

But an HDMI cable only uses two pins per color channel (TMDS Data0+/-,

TMDS Data1+/-, TMDS Data 2+/-), so I think a solution would be to design

a logic circuit that converts between the TDMS serial data to 24-bit parallel.

There must be chips that specifically are designed to do that.

Anyone knows about these chips ? Or has seen online a circuit board that

could be printed and assembled to do that ?

Otherwise a general-purpose programmable chip could do that, but it needs

to handle data at a very high frequency (100 MHz ?), frequency which can

be calculated :

f = total number of pixels (H x V for screen resolution) x 1/multiplier

x desired refresh screen frequency

where the multiplier can range between 1 and 24, depending on the number

of wires that are used to carry the signal

... leaving it at this stage for now.... :)

michael.

[Udi Finkelstein]

1. All RasPi has HDMI - A, A+, B, B+ and 2.
2. the B had the original RCA socket for composite video, while the B+ and 2 combined it with the stereo analog output in a 4-pin 3.5mm plug, like it is done in many cameras.
3. if you think you can easily convert the HDMI TDMS signals into a simple 24 bit parallel bus, you are naive. this is complex in so many levels, it is a project in its own.

just get an HDMI monitor and be done with it, or a composite monitor if you can live with the lousy quality. just be warned that for some reason HDMI monitors of small sizes will not be necessarily cheaper than full size monitors sure to economies of scale.
these monitors, BTW, are typically used by people who film using DSLRs and needs a small HDMI monitor to see what they are filming.

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[Udi Finkelstein]

You might want to take a look here:

I forgot to mention the DSI connector, which is also TDMS, but unlike HDMI which has many layers on top of it, is simpler.

http://elinux.org/RPi_Screens

[Michael Lew]

Udi's suggestion to buy an LCD screen that directly accepts HDMI is

a good solution - BTW, if anyone knows where to buy this in Israel, let

me know.

My question was how to use the RPi with an LCD screen that comes

with a display driver based on the SSD1963.

Apparently one solution would be to use the Guzunty, which is based

on a programmable Xilinx chip : https://github.com/Guzunty

michael.

[Yair Reshef]

hdmi / LCD screens you can find in car electronics shops. or go to har tzion to visit beltzer

or at  "antenot ratzon"., lavanda st. tel aviv. they deal with CCTV, cabling etc.

it will not be china price, but ....

if your looking for more industrial suppliers, there is "high-tech" magzine with many advertising palyers. i need to remined myself to give tami a subscription for the paper adittion. it might be free.

di you see tami suplier map?

https://www.google.com/maps/d/edit?mid=zgAcco0n89So.kxgrRyMrr1Mw&hl=en_US

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‏קיבלת את ההודעה הזו מפני שאתה רשום לקבוצה 'TAMI' של קבוצות Google.
כדי לבטל את הרישום לקבוצה הזו ולהפסיק לקבל ממנה דוא"ל, שלח אימייל אל hasadna+u...@googlegroups.com.
כדי לפרסם בקבוצה הזו, שלח אימייל אל has...@googlegroups.com.
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+972-50-6301212

[Udi Finkelstein]

I think cat screen might have composite inputs. this is OK too, since the raspi can drive those as well.
ofcourse, given the analog nature of the composite video signal  its of much lower quality than hdmi, let alone the resolution.
however if all you need is a low res 320x200 screen, composite is OK too.

[Yair Reshef]

ot

https://copterdeluxe.com/Professional-HDMI-to-AV-Interface-with-Remote-Control