# CRT circuitry

Discussion in 'Beginner Electronics' started by Bjarni Juliusson, Sep 14, 2005.

1. ### Bjarni JuliussonGuest

I bought a tiny little 5.5" B/W TV set, and I thought it would be an
interesting thing to do to take the tube and try and build myself a
little computer monitor - nothing fancy, just a device to take TTL
horizontal and vertical sync signals and a video signal and give me a
couple of hundreds of lines of picture at 50Hz.

So I've been surfing around now for a while to find some information on
the subject, and it's been very informative. But even though I have now
got a general familiarity with the workings of a CRT, I have not been
able to find anyone who has built any CRT control circuitry and written
about it on the web. It doesn't seem at all impossible though.

So does anyone have any suggestions? Any websites with detailed
information that is not completely over the head of a beginner? I don't
know much at all about analog electronics, being mostly a computer guy.
Or does anyone have enough knowledge to offer an example layout of such
a circuit for me to try?

I'm grateful for any help at all!

Bjarni

2. ### DBLEXPOSUREGuest

Quite an undertaking. My first thought is, "be careful" I am guessing the
anode voltage on that tube is 3 to 5Kv and will be present even with no
power is applied. Learn how to discharge the tube safely. If you are
nervous at all doing it, then you shouldn't be doing it, especially alone.
Use the, One hand in the pocket rule, Have a qualified tech demonstrate it
for you.

Learn and understand where the high voltage is located on the circuit board
and be conscious of it when fiddling with the circuit when it is live.

Secondly, the deflection circuits are not designed to run at typical
computer monitor frequencies. This might prove to be difficult. If you are
going to redesign the deflection circuits and have a limited knowledge of

Not trying to be discouraging, whether you successful or not you will
certainly learn something. But do be careful.

3. ### Oliver Hannaford-DayGuest

Hi,
Im doing a similar thing with a 1" Mullard Tube and found this website very
good:
http://www.electronixandmore.com/project/14.html
It uses a LM1881 and two 555's and thats basically it for the basic version,
he did a delux one for his oscilloscope which is a bit more complicated but
Im giving this a try first.
My LM1881's turned up today so as soon as I get some time I will be plugging
it in and seing what it comes out with.

Anyway good luck
Oliver Hannaford-Day

4. ### Bjarni JuliussonGuest

Check and double check. Don't worry about my safety.
Which is why I decided to go with a resolution close to the original TV
resolution, as I mentioned in the original post. If I can get 256 lines
at 50Hz, I'll be very happy.
It just so happens I found this:
http://www.hanssummers.com/electronics/equipment/spectrumanalyser2/

I found a small B/W junk TV/radio/cassette recorder, and when I looked
inside it had a very conspicuous chip labeled AN5151, so I googled for
datasheets. What I found was the site above. The guy (Hans) has done
precisely what I want to do: he took a small B/W TV with an AN5151 chip
in it and turned it into a computer monitor (he uses it for a spectrum
analyser). The AN5151 takes care of generating the sweep signals from
composite sync, and he built his circuit by simply drawing a diagram of
the board in the TV and moving the relevant components to a new board. I
think I'll do something similar. Hans' site has shown to me that this is
not an unrealistic goal.
take the voltages seriously and have read up on the matter. I am also
not completely unexperienced in electronics, just in this particular field.

Bjarni

5. ### Jasen BettsGuest

So You've figured out how to get that sync rate out of your video card?
(if not I have some suggestions)

That's half the battle, then all you need to do is combine the sync signals
and the video signal at the apropriate voltage levels and feed that to the
composite in (or to a rf modulator and to the antenna connection)

it may be possible to link directly into the sync circuits of the TV, but
doing that could require detailed knowledge of those circuits (like having a
service manual....)

Bye.
Jasen

6. ### Bjarni JuliussonGuest

Yes, since I'll be designing the video card.
I think you misunderstood my intentions. I'm not trying to hook my PC up
to my TV, I'm trying to build my own CRT control circuits and video
circuits. But see the website I linked to. I think I'll do it in a
similar way.