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Old 22 September 2017, 19:13   #1
Sinphaltimus
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Help understanding HDMI voltage needed...

The video says it all. Any help understanding this is greatly appreciated - [ Show youtube player ]
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Old 22 September 2017, 19:43   #2
majsta
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Ok here is what is going on and we did know about that long time ago since earlier versions of Vampire cards build for team members. There is back current from HDMI who is going back to Amiga motherboard. Somewhere around 5V and 50mA. That is happening because HDMi is powered directly from Amiga power supply so from 5V, however same voltage is present but with small amount of current on and HDMI device Tv set, amplifier or whatever. That current is low and won't damage anything that's why we didn't fix that. You can experiment for example to plugin HDMI then remove Vampire card from Amiga and you will see LED on Vampire lights up. power from HDMI is too weak to be used as power supply. Same thing you see when you use devices like TV box powered by android who connects on HDMI but takes power either from USB in same TV set or from external supply.
This voltage comes from pin 18 on HDMI and from there goes directly to Amiga VCC. This can be solved by placing diode between them BAT 60 or something like that. Since at the time I didn't even add LVDS shifters to create "real" HDMI and also didn't include plugin detection or I2C. This design we have regarding video out gone more than I ever expected that is possible. I was thinking that 640X480 is the max anyway.

Last edited by majsta; 22 September 2017 at 22:05.
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Old 22 September 2017, 19:47   #3
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@Sinphaltimus could you please try with the HDMI amplifier: http://www.ebay.com/itm/282418537451

It should prevent the back current.
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Old 22 September 2017, 19:51   #4
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If you have an understanding of HDMI can you tell me how my cable box knows when my TV is switch off and how I can disable this hand shaking.
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Old 22 September 2017, 19:56   #5
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Use some ducktape to cover pin 19.
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Old 22 September 2017, 19:57   #6
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Thanks ill check it out.
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Old 22 September 2017, 20:13   #7
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@majsta - Thank you! I'm thinking I don't have to worry about it but I may go with the diode solution just for peace of mind. I'm guessing just falt out cutting the +5v line (pin 18) is a bad idea.

@SHK - I really don't want to "try " something for the sake of it - if it is a known device to prevent back voltage then i would certainly go for it.


ALL - To be fair, the Vampire board puts out great HDMI quality for my screen. I was considering just a short extension cable to give me an HDMI port on the back of the Amiga instead of internal on the Vampire. But I didn't want to cause degradation of the signal. I figured a self powered splitter would be a good solution for dual display(presenting) or a future HDMI recording device for screen captured videos.

If there is definitive belief this will cause no harm, I'm OK with that. But I think I will look in to making an adaptor with a diode to limit the direction of the voltage to output only.

Just in case.
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Old 22 September 2017, 21:19   #8
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Quote:
Originally Posted by Sinphaltimus View Post
ALL - To be fair, the Vampire board puts out great HDMI quality for my screen. I was considering just a short extension cable to give me an HDMI port on the back of the Amiga instead of internal on the Vampire. But I didn't want to cause degradation of the signal. I figured a self powered splitter would be a good solution for dual display(presenting) or a future HDMI recording device for screen captured videos.
Give it at try. You will see if you get issues as the bit faults will be evenly distributed in the R, G and B byte values sent and will affect both the bits representing high values and low values, so you will see different pixels with very wrong colors.

Generally, hdmi is very tolerant below 5meter cable length.
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Old 22 September 2017, 23:46   #9
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Quote:
Originally Posted by majsta View Post
........ This can be solved by placing diode between them BAT 60 or something like that........
Could I just cut the 5v line and drop in this? -

https://solarbotics.com/product/dz5_1/

In reality I would probably make a small adapter HDMI straight through with a diode on pin 18. Just not sure what kind of diode rating I should be looking for.

Like two of these for the adaptor - http://www.mouser.com/ProductDetail/...xoCc_QQAvD_BwE
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Old 23 September 2017, 00:38   #10
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Not to butt in, but why not just lift pin 18 on the HDMI connector? Is it actually needed?
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Old 23 September 2017, 00:52   #11
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Originally Posted by grelbfarlk View Post
Not to butt in, but why not just lift pin 18 on the HDMI connector? Is it actually needed?
No, no problem, that's a great question. I thought I asked that but my brain never typed the question out...

I could of course just test it. I know that line 18 should be a purple wire not bundled with others within a cable that adheres to standards; So I was thinking of finding that wire in an hdmi cable and simply cutting it to see what would happen and if things went south, dropping in the diode across the open wire.

I thought of that after doing a price check on those HDMI breakout boards. Almost 10 bux each makes this an expensive adaptor when I could do the same on a cheap cable.

So thanks for butting in, At least now the question is asked.
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Old 23 September 2017, 01:00   #12
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No, no problem, that's a great question. I thought I asked that but my brain never typed the question out...

I could of course just test it. I know that line 18 should be a purple wire not bundled with others within a cable that adheres to standards; So I was thinking of finding that wire in an hdmi cable and simply cutting it to see what would happen and if things went south, dropping in the diode across the open wire.

I thought of that after doing a price check on those HDMI breakout boards. Almost 10 bux each makes this an expensive adaptor when I could do the same on a cheap cable.

So thanks for butting in, At least now the question is asked.
If it's only for DDC, I assume it's not really used on the Vampire, but who knows maybe the display device wants that to be there. If I get time this weekend I might have a try at lifting that pin.

On the CDTV at least, 5V is running through much of the motherboard while it is off to wait for the wake command on the remote and to drive the clock and stuff, that gives me a tiny bit of concern that the TV might still be driving that very low signal too, maybe even when the TV is on another input.
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Old 23 September 2017, 12:26   #13
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@Sinphaltimus I wouldn't bother at any of that, leave it as is, like I told you it is ok. after all same thing going on on my setup and like I told you if I had feeling that this is problem I would fix it 2 years ago.
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Old 23 September 2017, 12:28   #14
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@Sinphaltimus I wouldn't bother at any of that, leave it as is, like I told you it is ok. after all same thing going on on my setup and like I told you if I had feeling that this is problem I would fix it 2 years ago.
Alrighty then. I bow to the expertise. I will not do anything to change this.
Thank you again.
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Old 25 September 2017, 01:36   #15
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Quite common with poorly designed HDMI devices and HDMI standard is partially responsible for this - normally this should not happened but even experienced companies doing such mistake in their HW - connecting pin 18 to common 5V line where it should be connected to system in controlled and current limited way.
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