RCA ? TV: text-output.

Yes.

TVs are seriously bandwidth limited. Monitors don't have to support NTSC color or audio, so they can have better bandwidth. If you're serious about the subject, you might want to track down a copy of Don Lancaster's Cheap Video Cookbook; it explains the issue and discusses ways to mitigate it.

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roger ivie 
rivie@ridgenet.net

yes. UHF in the UK, VHF in most other places. picture only, no sound.

yesh, and not just the input

something like dasher?

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For a good time: install ntp

Try here:

Bill Garber

Probably. A keyboard costs about the same as a mouse and a system with only a keyboard is far more useful than one with only a mouse. Secondly Dasher and various onscreen keyboards already exist to do this and are in the repositories.

What's dasher ?

This is my theory:

TV: RF-> IF -> Audio/Video separate -> Video -> display

RPi/DVD/Tuner -> Video -> display

So theoretically the last 2 stages are the same; except that for a TV, the pre-Video stages are so punishing that the video signal is so dirty that TVs use poor-quality/cheap [Video -> Display] stage/s.

TV's don't need the resolution in the [Video -> Display] stage/s. So then RPi's RCA was not made for TVs else they would have used bigger font. Can I set RPi's non-X font bigger. The idea is to use existing TVs, without any mods.

== TIA.

Eh? pretty sure it is for TVs since composite monitors are vanishingly rare these days compared to old analogue tellies.

On Sun, 17 Nov 2013 14:57:55 +0000 (UTC), Unknown declaimed the following:

Even ignoring audio/video filters in the input stream...

NTSC tends to only support 640x480 INTERLACED as digital display (the other 32 scan lines of the 512 lines is for handling vertical retrace, and sync timing).

Interlacing at NTSC* rate will cause flickering of alternating horizontal lines, so most fonts are probably sized to use two scan lines for horizontals (one scan line fades as the other is being drawn). So...

480 scan lines / 2 lines "deinterlace" gives 240 effective rows. Assume a font 12 rows tall (including leading) and you can just squeeze 20 lines of text. The font is probably using 8 "pixels" width including intercharacter spacing -- 640 / 8 => 80 characters across.

Now toss in the analog filtering (cut off part of the bandwidth where the audio signal is carried, smoothing high frequency components of the video) and your net may only support 64 characters by 16 lines of text (which is what the original TRS-80 monitors produced... The monitor for the TRS-80 Model 1 was a B&W RCA TV with the tuner module removed and the holes for the knobs covered by a name plate -- I know, Sears sold the TV and it was identical to the monitors down the mall at RatShack )

The TRS-80 model 4 obtained 80x24 by removing some interline spacing (the 2x3 block graphics character set revealed this -- the bottom two blocks in each character cell were half height).

• PAL gave more scan lines, but at an even slower update frequency.

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and of course comparing any B&W screen with a Colour TV isn't the same.

The B&W screens used a plain coating of phosphor and scanned across it in simple lines using a single electron beam.

Colour CRT screens are complex beasts with a matrix of red, green and blue phosphor dots on them and three beams that go through a metal grid in order to hit the right dot. That means that the resolution of the colour screen is limited by the size and position of the holes in the grid and the dots on the screen, whilst the B&W screen is only limited by the number of scan lines and how fast the beam can switch.

Hence a cheap B&W monitor can handle 640 or more horizontal dots with some ease, but a medium priced colour one tends to blur them together a bit.

Disclaimer: haven't tried it myself.

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roger ivie 
rivie@ridgenet.net 
> 
>

The ZX80 was introduced in '79/80

Yes,

The CVBS signal was generated on board but fed to a modulator to produce a RF signal for TVs. They did not usually include baseband CVBS outputs unless you modded the machine to pick off the signal before the modulator.

The question is perhaps moot though, since even in exclusively digital countries such as the UK, most TV equipment is stall capable of displaying an analogue signal if presented with one.

Secondly, given the choice of taking the unmodulated video from a pi and feeding it into a compatible "video in" socket on the TV, it will always be preferable to taking the trip to RF and and back.

Obviously... (for those that have RCA inputs for such things - in these parts RCA sockets have generally been superseded by SCART)

You are fighting a loosing battle on older TVs due to the limitations of the technology.

Modern LCD HD TVs can do respectable computer displays via VGA style connections, and obviously even better via HDMI. But with classical non HD CRT based sets, non over-scanned display resolutions of more than about 640x256 (640x200 on NTSC sets) are always going to be a bit disappointing for computer use.

They probably included whatever was easy to get out of the hardware.

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Cheers, 

John. 

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Unless he is referring to the MK14 circa 1977.

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Graham. 

%Profound_observation%

I had a feeling that only had external video as an option, with the default being the built in seven segment LED displays?

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Cheers, 

John. 

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640x480 interlaced at NTSC rate is at best borderline usable for text. At least, that was the case with my old Amiga 500s and 1000. The interlacing makes the text flicker, even if the monitor can display single pixels. For decently usable text, my experience is you want 320x240 non-interlaces.

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Robert Riches 
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There was an add-on video board for the Mk14. I never had one though.

Gordon

I have a vague feeling I may have seen one running in the flesh once, but have never used one - just a tiny bit before I really got into computers (my intro being building a ZX80)

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Cheers, 

John. 

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It supports a text resolution of 32 x 16 or a Graphics Resolution of

64 x 64 according to

Can't find anything about how it interfaced with the VDU, I suppose the buyer saw to that himself, so it could be phono.

Hobbyists would likely want to use their existing TV, and TVs of that time rarely had a base-band input. I used to convert old TV tuners into modulators for my projects.

TTL level video gave very sharp results, until the phosphor burn inevitably took its toll.

--
Graham. 

%Profound_observation%

(the

where

spacing

OK thanks. I knew all the details but just failed to infer the conclusion, which you have done so well. And that's even after I though about it quite a lot.

OK thanks, that works; I confirmed several font-sizes; plus it leads to the menu to set-up the keybrd.

But my kybrd/S still have problems with swapped:@ , "

Linux docos on kybrds need to be rewritten by engineers/scientist and not drama students who can't resist the word "you".

Most Linux distros default to the US keyboard layout: this is a typical symptom if you are using a UK keyboard without configuring the keyboard driver. If you're using a graphical desktop you'll find a 'Keyboard' configuration tool in the system setup menu.

Normally, when you install Linux off the net or a DVD image, the installler takes you through setting the keyboard and choosing a language, but of course you don't use the installer with the RPi.

If the worst comes to the worst, read "man 5 keyboard" and edit /etc/default/keyboard with your favourite text editor.

I'm using a UK 105 key Benq keyboard (it has the 3x3-block print scr|scroll|pause ... with 4 cursor keys under it just right of the main keyboard and a separate numeric block at the right-hand edge. My copy of /etc/default/keyboard looks like this:

# KEYBOARD CONFIGURATION FILE

# Consult the keyboard(5) manual page.

XKBMODEL="pc105" XKBLAYOUT="gb" XKBVARIANT="" XKBOPTIONS=""

BACKSPACE="guess"

I don't remember how that got set - sorry.

Keyboards are a bit of a black art to configure on any computer that uses PC-style keyboards, i.e. those that send keycodes and expect the system drivers to convert those to ASCII or Unicode.

Old-style hard-wired ASCII keyboards were a lot simpler to figure out, though less flexible.

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