iMac wobblevision

[Circuitbenders]

Does anyone happen to know if the screen / monitor part of an original CRT iMac shuts down automatically if its disconnected from the motherboard or onboard graphics card or whatever it is thats in there.

Obviously PC monitors can't be wobblevisioned unless you keep them plugged into a graphics card as they shut down automatically when theres no signal on the VGA cable  but seeing as i wouldn't imagine that the iMac designers ever thought the screen would be detached from the internal graphics card they wouldn't have built in that feature. After all, you more or less need a hammer and chisel to get into an iMac anyway, and i know you can wobblevision Mac Classic / SE machines.

[Circuitbenders]

You see 

[andy_wheels]

i'm liking that.... liking it a lot... 

so no auto shutoff then??

[Circuitbenders]

Not on the old Mac classic's or SE's it would appear, obviously Apple weren't trying to be helpful with auto shutoff nonsense back in 1988. Now if i can just get hold of one of the rare Mac Colour machines from that era......

Not tried an IMac yet.

[Circuitbenders]

Theres a demo of my Mac SE here: http://www.circuitbenders.co.uk/demos/wobblemacdemo.avi

Dancing to the standard bit of the Crystal Method that all wobblevisions seem to love. I think its DivX encoded.

[ne7]

i think i read somewhere u can wire up the pins of the plug on a vga monitor to fool it into thinking that there is a signal

[Circuitbenders]

i think i read somewhere u can wire up the pins of the plug on a vga monitor to fool it into thinking that there is a signal

If you'd just like to read that again somewhere and then tell me how its done!

I've been looking for any details of how to do that for a while now. As far as i can gather a graphics card constantly sends a series of pulses to the monitor to keep the display in sync with the card. If these pulses aren't there then on older monitors it just loses sync and displays nothing, which is potentially useful if it doesn't actually shut the tube down. Newer monitors just shut down the tube and go into standby mode as soon as they lose sync with the graphics card i.e. if there isn't a card attached.

On the other hand i could have this completely wrong

[spineofgod]

i think i read somewhere u can wire up the pins of the plug on a vga monitor to fool it into thinking that there is a signal

i don't think its possible. i've been looking for ages and can't find any information about how to do this anywhere

[angrydroid]

http://www.epanorama.net/documents/pc/vga_bd15.html has some schematics... go to the very end.

I suspect if you maintained a steady +5v to the H-sync and V-sync that might be able to do the trick. Hope this helps.

Also this might be applicable.

[catweazle]

Interesting project, *mmmh if I had more time a day!*

You can fool older VGA monitors by setting pins to ground, like  angrydroid   mentioned.

Code Select Expand


Monitor ID detection pin assignments
4    11   12      (Pin)
ID2  ID0  ID1   (Description)

n/c  n/c  n/c   no monitor
n/c  n/c  GND   Mono monitor which does not sopport 1024x768
n/c  GND  n/c   Color monitor which does not support 1024x768
GND  GND  n/c   Color monitor which supports 1024x768

GND menas connected to ground
n/c means that the pin has not bee connected anywhere

... tying  pin 12 to GND should do it.


But newer monitors use other more complex protocolls (I2C serial bus), to emulate/fool that you need
an microcontroller. So I would use an old monitor not a LCD monitor

I am not shure if it is enough to fool the "monitor presence detection". The synchronisation (H/V Sync) has
to be correct, too. So a little circuit is needed to generate the sync signals.
check this out.... Composite tio RGB converter for example
http://elm-chan.org/works/sc/report.html
http://www.epanorama.net/links/videocircuits.html

http://www.epanorama.net/documents/pc/vga_timing.html
Two little  NE555 (or one NE556)  oscillator on the sync pins.

H-Sync  (pin 13)   31,5 kHz
V-Sync  (pin 14)   60 Hz 
but one of the sync signals has to be a negative voltage!

see http://lslwww.epfl.ch/pages/teaching/cours_lsl/ca_es/VGA.pdf


But I could be wrong of course, maybe grounding pin 12 does it perfect.

[djsynchro]

Paul, do you discharge the CRT when you mod the Mac Classics? And if yes, do you do it with a wire or do you use a resistor as well? I have a Classic and i want it wobbly.... I don't have the keyboard or mouse anyway... found it in the trash (screen works perfect though) I've seen pictures from the inside... 4 wires pretty easy mod otherwise.

Thanks in advance!
:-)

[Circuitbenders]

To be honest i don't really want to go near that much voltage and so i don't try to discharge the thing. I just be very very careful not to touch anything except for the deflection yoke.

Theres some good information here http://www.laserfaq.org/sam/crtfaq.htm#crtsdc

[djsynchro]

Yeah... was thinking about doing the same thing. Apparently when you work inside it for a length of time you need to keep it grounded anyway as the voltage gets stored in the glass and can come back even if the CRT was discharged (is what I've been reading on the Net!)

I have anutha question if you don't mind: Can you get at the four wires just by taking the cover off?
I was reading here:
http://geektechnique.org/projectlab/707/how-to-make-mac-se30-audio-visualizers
He's taking the whole CRT tube out & shit... (he did paint them though) I don't want to do that if I don't have to...

Audio goes straight into the Yolk? No resistors or anything?
Cheers!

[Circuitbenders]

There are just four wires going into the deflection yoke coils. They are usually connected to the upright board with a big plastic connection block. I can't remember off the top of my head which way round you should connect them to the inputs to give the best results so you'll have to experiment.

Yoy can just pull the back off the casing and everything you need to get at is exposed, if you can find a torx bit holder that is long enough to get at the screws under the case handle area.

Audio can go straight into the yoke with no resistors.

By the way, those people are idiots if they think a pair of rubber washing up gloves are going to protect them. One sharp point on a solder joint and thats a whole lot of volts through the glove. Obviously they are better than nothing but i can see people getting way too overconfident that they won't get electrocuted wearing a pair of those.

[djsynchro]

Thanks again sir Paul!!!!

You're right about the gloves... I am going to get try some thicker ones and i'd stil be REALLY careful not to touch the wrong shit!!! I was going to bring out the wires coming off the board as well, I think it's a different effect to leave either X or Y connected and have music on the other connections.. It think you can have some sort of bar display that way.... (Cemstron?)

That connector plastic block... What would be cool is to have the right male and female connectors then I can just pull  lit off the PCB, plug in 2 new cables and connect to the patchbay do you know what connector it is? Might be able to get it out of an old PC...