Software control of LCD vs. Video Out - General Discussion and Assistance - CHDK Forum
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Software control of LCD vs. Video Out

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Offline waldo

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Software control of LCD vs. Video Out
« on: 03 / May / 2008, 15:23:13 »
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I have a camera setup where I have a Video Out cable plugged into the camera.  The camera shuts off its LCD when this cable is plugged in.  I would like to be able to briefly see the image on the LCD without having to unplug the cable.  I believe this is possible to do, but I'm not sure exactly how to implement all of it.

Here's what I know so far:
My camera (a SD400) sets bit 5 in physw_status[0] when the video cable is plugged in.
Modifying the value of physw_status[0] inside my_kbd_read_keys() will change the behavior of the video cable being plugged in - I can either force the LCD to be on all the time or force it to be off all the time, regardless of whether the video cable is inserted.

Here is the test code I placed inside my_kbd_read_keys() to force the LCD to be on all the time.
   physw_status[0] &= ~0x0020;
   
The following code turns the LCD off and the video output on all the time:
   physw_status[0] |= 0x0020;

So far, so good - this proves I can control LCD vs. Video Out via software. :D

BUT, the camera will only notice that I changed physw_status when I physically plug or unplug the cable. :(

Maybe the way to force the camera to use my value of physw_status is to use a technique like in kbd_sched_press(), but I do  not understand that code well enough to know how.  Can anyone help me with this?
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Offline PhyrePhoX

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Re: Software control of LCD vs. Video Out
« Reply #1 on: 03 / May / 2008, 16:32:14 »
hm i have seen a similar thread here, about the same topic, i cant find it though. basically it has the same question. dont remember if it was solved though.
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Offline Microfunguy

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Re: Software control of LCD vs. Video Out
« Reply #2 on: 03 / May / 2008, 16:56:08 »
Quote from: PhyrePhoX on 03 / May / 2008, 16:32:14
hm i have seen a similar thread here, about the same topic, i cant find it though

It was possibly by myself but I cannot find it.

Maybe it was on DPReview ?

I wanted that feature so that I could plug electronics into the video output of two cameras and measure the time-difference of the synch pulses without blanking the screen.

The current  software-synching method is infinitely better but I am still interested in controlling an external display.

Will have a play with it.


David
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Offline Microfunguy

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Re: Software control of LCD vs. Video Out
« Reply #3 on: 04 / May / 2008, 18:59:22 »
Quote from: waldo on 03 / May / 2008, 15:23:13
I can either force the LCD to be on all the time or force it to be off all the time, regardless of whether the video cable is inserted.

Here is the test code I placed inside my_kbd_read_keys() to force the LCD to be on all the time.
   physw_status[0] &= ~0x0020;

On my A620 that would be 0x02000000.

Does not seem to work.

Did you find more than one bit changed when you plugged-in the video ?


David
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Offline waldo

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Re: Software control of LCD vs. Video Out
« Reply #4 on: 04 / May / 2008, 19:39:55 »
David, No, only one bit changed.  You can see this if you enable the debugging "misc values", but you have to plug the video cable into a TV to see the bit change.
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Offline PhyrePhoX

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Re: Software control of LCD vs. Video Out
« Reply #5 on: 22 / October / 2008, 07:28:40 »
reviving this topic: finding an implementation to this "problem" for all camera types would be a very great thing.
a) for people who want to shut off the display to save energy (without the use of a av plug)
and
b) (thats my primary interest) to be able to use BOTH lcd display AND av-out for "studio sessions" when for example your client wants to see what you are shooting on a big TV screen.

may i ask how these values have been found?
also i understand that the "shutting off" of the display using this method is no BIG energy saver, as energy is spent on the av port. but this is another thread i will revive :D
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Offline TheJez

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Re: Software control of LCD vs. Video Out
« Reply #6 on: 04 / November / 2008, 09:10:52 »
Quote from: waldo on 04 / May / 2008, 19:39:55
David, No, only one bit changed.  You can see this if you enable the debugging "misc values", but you have to plug the video cable into a TV to see the bit change.
Hmmm... I just noticed this remark. Could this be an alternative way to do remote triggering? (In stead of using the USB triggering with a battery.) I am thinking how the camera 'knows' that a tv is connected... It is only output, so apparently there are some electronics in the camera that measure the impedance of the video connection and compare it to some threshold. If impedance>threshold, then no tv is attached, else a tv is attached.

Can anybody elaborate on this?

Thanks,

TheJez
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Offline waldo

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Re: Software control of LCD vs. Video Out
« Reply #7 on: 04 / November / 2008, 09:20:37 »
Phone plugs that sense when something is plugged in have physical switch contacts that open and close when something is inserted.  There is no sensing of impedance.
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Offline TheJez

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Re: Software control of LCD vs. Video Out
« Reply #8 on: 04 / November / 2008, 09:25:23 »
Thanks, please correct me if I'm wrong. But the remark "you have to plug the video cable into a tv to see the bit change" kind of gave me the impression that there is more involved than just the physical switch in the camera that detects if a plug is inserted or not...

I don't have my camera at hand, but I'll just have to give a try, I guess...

Thanks again!

TheJez

Edit: Ah, now I understand (I think!). The bit changes as soon as you plug in the connector to the camera, but because the display switches off, you can only SEE it when you attach a tv. Sorry, my misunderstanding....
« Last Edit: 04 / November / 2008, 09:28:18 by TheJez »
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Offline PhyrePhoX

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Re: Software control of LCD vs. Video Out
« Reply #9 on: 12 / November / 2008, 18:38:48 »
hm, i now tested tvout vs lcd, my physw_status[0] is as follows:

with no av cable plugged in: 20009203
with av cable plugged in:            9203 (without the leading zeros).

dont really know what to make out of it. i really need the feature that the lcd will stay active when the av-cable is plugged in. hm.
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