| promy |
I recently build my first projector out of HQI 250watt and a liliput 7inch.
It runs smooth, but there is a minor problem...
When i connect it with a short vga cable which came with my lcd (1m or so) it displays a nice clear image.
But when i connect it with a superior quality cable (the one with the goldcolored connectors) of 5m, i get a ghost image slightly to the right (mostly red).
So i was thinking if there was a way, to amplify the vga signal so that this isn't the case anymore?
Since i like DIY i was thinking maybe i can use some sort of op amp like used in stereos etc
There are only 6 wires used, so that isn't that much...
Is there anyone with a solution to my problem, or someone who can tell me how to make this amplifier
And if it would be able to make 2 outputs from one input, it would be even better ;-) |
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| dhaen |
If this is truely "good" 75 ohm cable, then the problem is one of source or load impedance (matching).
The ringing is a reflected signal in the cable.
The normal way this is done is that the output of the driver chip (or discrete amp) is fed to a 75R resistor then to the cable inner. At the receive end, there should be a 75R resistor to ground (cable outer).
Also check that the cable outer (shield) gets to ground at both ends.
Of course it could be that the cable is **** :(
An amplifier is not the answer for this cable length ;) |
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| promy |
You say, that it should be grounded at both ends.
Now the ground is passed on, from the ground of the cable, to the ground of the 2nd cable going to the liliput.
Would it help, to connect this ground to the ground of the electricity net? or would that be worser?:confused: |
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| dhaen |
| No, the ground I'm talking about is the local circuit ground. Signal ground. Ie where the decoupling caps of the circuits are connected to. |
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| promy |
since the liliput, has only 6 wires...and should be connected to pins 1,2,3,6,13 and 14 which represent R, G, B signal, R ground, H and V sync (from http://www.wschmid.de/Beamer.htm) :o
so it seems, that G and B are not grounded...
And the pin 5 on vga (ground) seems not to be connected (only the outer shielding is connected)
Would it be advisable to interconnect the G and B to the R ground, and maybe to the ground wire (pin 5)?:confused:
or is this not the way to do it? :confused:
And i was thinking...in the layout, the vga cable internally is next to a 220cable... (for the HQI lamp) can this be bad? or should the shielding easily filter this out? |
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| dhaen |
Each cable's shield (R, G & B) should be connected to local ground at both ends.
Sometimes they are connected together inside connectors. If so, a single local earh wire or pin is sometimes used. |
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| promy |
corrected the problem :)
when is soldered the ground pins (so pin 5,6,7,8 and the outer together, i instandly lost the blurry image :) )
So if anyone has the same probs, they know what to do!
Thanks dhaen for your help with this little annoying problem! |
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| dhaen |
Glad to have a satisfied customer :)
Enjoy:cool: |
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