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vijayv |
2010-11-13
, 18:46
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Posts: 58 |
Thanked: 10 times |
Joined on Jan 2010
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#21
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It did not work for a very long time for me.. finally if I did not insert fully and if the TV part is plugged in first it works. I think for many the cable connector is loose or is not oriented properly such that a stable connection is made when fully inserted..
Originally Posted by wierdo
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2010-11-20
, 13:09
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Posts: 17 |
Thanked: 11 times |
Joined on Nov 2010
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#22
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I've got a Philips Matchline TV, and this is really an interesting beast.
When on, the video input has a voltage of about 145 mV, no matter what channel is selected.
When off, no voltage is on video input (fortunately...), but a resistance of about 61 Ohm. This is close enough to 75 Ohm for the N900.
However, when the TV is on, the N900 apparently isn't able to correctly measure the impedance due to the voltage which is also present (... and neither is my Ohm-meter able to get a meaningful reading...)
However the following procedure works:
1. Make sure TV is off
2. Plug in cable into TV
3. Plug in cable into N900
4. Switch TV on (which takes a looong time on this old green CRT TV due to preheating...)
If step 2 is performed while TV is on, it won't work.
When cable is not plugged into N900, /sys/devices/platform/nokia-av/detect is 3
When plugging it in while TV is off, /sys/devices/platform/nokia-av/detect stays 3, and stays 3 after switching it on.
When plugging it in while TV is on, /sys/devices/platform/nokia-av/detect becomes 0, and becomes 2 when switching the TV off, and reverts to 0 when switching it on again (... and still no picture).
So, it looks as if there is a mechanical sensor in the N900 which detects presence of a cable, and an impedance sensor.
Impendance sensor takes a measurement after cable is connected. If impedance "close enough" to 75 Ohm, TV-Out is activated. If not close enough, it keeps probing, sets /sys/devices/platform/nokia-av/detect to 2 if impedance ok, but keeps on an sets it back to 0 if not ok.
I've also got a projector, which has "auto-select input", and which only has the correct impedance while the composite input is selected. So the N900 doesn't send a signal if not the correct input is selected, but the projector will never select the input because there is no signal... Fortunately this auto-select "feature" can be turned off on the projector.
But wouldn't it be easier if there was a way to manually telling the N900 that yes, a TV-like device is connected, and that it just should start sending the damn signal? Unfortunately, echoing 2 into /sys/devices/platform/nokia-av/detect doesn't help (Permission denied, even as root). And even bind-mounting a file containing 2 over it doesn't work either...
When on, the video input has a voltage of about 145 mV, no matter what channel is selected.
When off, no voltage is on video input (fortunately...), but a resistance of about 61 Ohm. This is close enough to 75 Ohm for the N900.
However, when the TV is on, the N900 apparently isn't able to correctly measure the impedance due to the voltage which is also present (... and neither is my Ohm-meter able to get a meaningful reading...)
However the following procedure works:
1. Make sure TV is off
2. Plug in cable into TV
3. Plug in cable into N900
4. Switch TV on (which takes a looong time on this old green CRT TV due to preheating...)
If step 2 is performed while TV is on, it won't work.
When cable is not plugged into N900, /sys/devices/platform/nokia-av/detect is 3
When plugging it in while TV is off, /sys/devices/platform/nokia-av/detect stays 3, and stays 3 after switching it on.
When plugging it in while TV is on, /sys/devices/platform/nokia-av/detect becomes 0, and becomes 2 when switching the TV off, and reverts to 0 when switching it on again (... and still no picture).
So, it looks as if there is a mechanical sensor in the N900 which detects presence of a cable, and an impedance sensor.
Impendance sensor takes a measurement after cable is connected. If impedance "close enough" to 75 Ohm, TV-Out is activated. If not close enough, it keeps probing, sets /sys/devices/platform/nokia-av/detect to 2 if impedance ok, but keeps on an sets it back to 0 if not ok.
I've also got a projector, which has "auto-select input", and which only has the correct impedance while the composite input is selected. So the N900 doesn't send a signal if not the correct input is selected, but the projector will never select the input because there is no signal... Fortunately this auto-select "feature" can be turned off on the projector.
But wouldn't it be easier if there was a way to manually telling the N900 that yes, a TV-like device is connected, and that it just should start sending the damn signal? Unfortunately, echoing 2 into /sys/devices/platform/nokia-av/detect doesn't help (Permission denied, even as root). And even bind-mounting a file containing 2 over it doesn't work either...