Main > Monitor/Video Forum
HDMI to Old CRT
PL1:
--- Quote from: Zebidee on November 26, 2023, 04:49:36 pm ---PL1: If you put a resistor between the wiper and the GND you change the behaviour of the pot (in terms of voltage response) to approximate a log curve (or is it anti-log? always confusing), rather than linear. This might well be appropriate and feel "natural" for the Atari 2600 paddles, but beyond the scope of what I'm talking about for this mod.
--- End quote ---
Different application and different connections, but it's still a combination of a pot and a fixed resistor. ;D
The Atari paddles have pots wired as variable resistors. (2 wires)
Arduino A/D inputs can only read voltage (not resistance) so the extra resistor was added externally so the original paddle wiring wouldn't need to be modified to make it work as a voltage divider. (pot)
Scott
Zebidee:
--- Quote from: abstract3000 on November 26, 2023, 04:33:18 pm ---Thanks for the Feedback, much appreciated.
...
So This is the Top side, I know it's painfully obvious what I marked but just indicating what I was looking at. And the orientation of the Trim Pot
So here is the Explanation I should say for lack of better words.
The Red Circles indicate the Pins on the Trim Pot
Left pin goes to a Jumper (No Jumping pin disconnected) The Other side of that Jumper goes to Pin 14 (H-Synch)
Center Pin Went to the 75Ohm Resistor (Now removed) Then to Ground
--- End quote ---
Oh wow this is very revealing. A few points that were not apparent from the schematic.
1) WTF/What/why is that pot/jumper connected to VGA pin 14? That is the vertical sync pin.
It should be connected to a 5v source. On some VGA cards 5v is available from VGA pin 9. There are also 5v sources available from the TV.
2) Looks like the 75R resistor was attached to the wiper+GND originally, rather than the output+GND as the schematic says. It is still pulling the voltage very low. Try replacing it with a larger value like 1K.
--- Quote ---The Right Pin Goes to a Diode, then Back to the TV Motherboard I assum to Blanking.
Here is a Closeup of the Diode
--- End quote ---
3) That diode is completely new news to me. It will pull the blanking voltage down even further (~0.7v). You probably don't need it there anyway, remove it [edit: easier to just bypass it with a short wire], it may be causing issues.
--- Quote ---In other news I went through and tried every setting in the service menu, managed to fix the Vertical Overscan, but nothing with RGB Cuttoffs or any other setting made any sort of noticeable difference besides "tone" which did what it sounds like yet not a solution. I just saw The previous posts, but didn't get a chance to read closely through them as I wanted to get you guys the Exact information of what was happening. I will look over those now.
--- End quote ---
I'm not worrying about this much for now. Get the blanking right first.
--- Quote ---@Zebidee, I like your solution for adjusting the voltage, those pots you used could you provide me a link to the specific ones that would be needed on Mouser or DigiKey? and those solderless connectors I really like, what are they called for searching purposes?
--- End quote ---
The specific pots I used are Bourne 500R, but as I mentioned above 200R would be sufficient.
https://www.bourns.com/products/trimpot-trimming-potentiometers/trimpot-trimming-potentiometers-multiturn/product/3296
To buy, search for:
"bourns cermet multi turn potentiometer 3296W-1-201LF" for the 200R variety, or;
"bourns cermet multi turn potentiometer 3296W-1-501LF" for the 500R.
I see that they are available on both Mouser and Digikey, as well as other online marketplaces.
Zebidee:
--- Quote from: PL1 on November 26, 2023, 05:34:35 pm ---
--- Quote from: Zebidee on November 26, 2023, 04:49:36 pm ---PL1: If you put a resistor between the wiper and the GND you change the behaviour of the pot (in terms of voltage response) to approximate a log curve (or is it anti-log? always confusing), rather than linear. This might well be appropriate and feel "natural" for the Atari 2600 paddles, but beyond the scope of what I'm talking about for this mod.
--- End quote ---
Different application and different connections, but it's still a combination of a pot and a fixed resistor. ;D
The Atari paddles have pots wired as variable resistors. (2 wires)
Arduino A/D inputs can only read voltage (not resistance) so the extra resistor was added externally so the original paddle wiring wouldn't need to be modified to make it work as a voltage divider. (pot)
Scott
--- End quote ---
Right. We/You are measuring voltage not resistance. Your example has only 2 pins connected, thus it is just a single variable resistor. Even so, it works as a voltage divider because there is another resistor between output and GND.[edited, corrected, condensed]
As you say, "Different application and different connections, but it's still a combination of a pot and a fixed resistor. ;D". Very true.
abstract3000:
--- Quote from: Zebidee on November 26, 2023, 05:44:26 pm ---
Oh wow this is very revealing. A few points that were not apparent from the schematic.
1) WTF/What/why is that pot/jumper connected to VGA pin 14? That is the vertical sync pin.
It should be connected to a 5v source. On some VGA cards 5v is available from VGA pin 9. There are also 5v sources available from the TV.
--- End quote ---
Sorry please take another look at the photo, I updated my mistake. That Jumper was left on the board and I was told it was for testing, and not to bother with it. My guess is the other side is related to Pin 13 and it was when he was playing around with the Synch Signals.
--- Quote from: Zebidee on November 26, 2023, 05:44:26 pm ---2) Looks like the 75R resistor was attached to the wiper+GND originally, rather than the output+GND as the schematic says. It is still pulling the voltage very low. Try replacing it with a larger value like 1K.
--- End quote ---
So it would have been on the Left pin not the Wiper, but I can try putting a 1K resistor in it's place instead to see what that does. The Wiper (center from my understanding is connected to the right pin)
--- Quote from: Zebidee on November 26, 2023, 05:44:26 pm ---3) That diode is completely new news to me. It will pull the blanking voltage down even further (~0.7v). You probably don't need it there anyway, remove it [edit: easier to just bypass it with a short wire], it may be causing issues.
--- End quote ---
Ok so I Can look at a way to pypass the diode completely, I was thinking the 5V may be coming from the TV to the right pin through the diode to ensure it doesn't somehow find its way back as precautionary, but I could have that completely wrong.
Zebidee:
--- Quote from: abstract3000 on November 26, 2023, 07:06:08 pm ---
--- Quote from: Zebidee on November 26, 2023, 05:44:26 pm ---
Oh wow this is very revealing. A few points that were not apparent from the schematic.
1) WTF/What/why is that pot/jumper connected to VGA pin 14? That is the vertical sync pin.
It should be connected to a 5v source. On some VGA cards 5v is available from VGA pin 9. There are also 5v sources available from the TV.
--- End quote ---
Sorry please take another look at the photo, I updated my mistake. That Jumper was left on the board and I was told it was for testing, and not to bother with it. My guess is the other side is related to Pin 13 and it was when he was playing around with the Synch Signals.
--- End quote ---
I think I understand. So VGA 13/14 is not connected or related to the blanking? Good, leave it for now.
--- Quote ---
--- Quote from: Zebidee on November 26, 2023, 05:44:26 pm ---2) Looks like the 75R resistor was attached to the wiper+GND originally, rather than the output+GND as the schematic says. It is still pulling the voltage very low. Try replacing it with a larger value like 1K.
--- End quote ---
So it would have been on the Left pin not the Wiper, but I can try putting a 1K resistor in it's place instead to see what that does. The Wiper (center from my understanding is connected to the right pin)
--- End quote ---
I'm confess to being completely confused now. As we just discussed with PL1, there are many ways to wire a pot for different outcomes. Your schematic shows the 75R+GND connected to output. This will pull your blanking voltage quite low.
One terminal is input, one is output, one is resistor->GND. Your pot is 1K? So I suggest a 1K resistor, 75R is too low.
If you had the output wired to the wiper then it would be like this:
1) 5v input
2) blanking output
3) resistor -> GND
--- Quote ---
--- Quote from: Zebidee on November 26, 2023, 05:44:26 pm ---3) That diode is completely new news to me. It will pull the blanking voltage down even further (~0.7v). You probably don't need it there anyway, remove it [edit: easier to just bypass it with a short wire], it may be causing issues.
--- End quote ---
Ok so I Can look at a way to pypass the diode completely, I was thinking the 5V may be coming from the TV to the right pin through the diode to ensure it doesn't somehow find its way back as precautionary, but I could have that completely wrong.
--- End quote ---
So.... the blanking 5v voltage is sourced from the TV somehow? Guess that's all I need to know for now.
The diode will only pass current one-way, but in doing so it drops voltage ~0.7v. I suspect that your blanking voltage doesn't get very high anyway, so this will just make it worse.
For now, don't remove the diode. Just solder a short wire (such as an offcut component leg) over the diode's terminals to bypass the diode completely. Much easier than removing the diode, and easier to undo later if you want to.
What we want to see is a large range of voltage (~0 to ~5v) at the pot's output. You can do this measurement yourself, at the pot's high/low limits, with a multimeter.