The Sinclair QL Forum

Peter wrote: ↑Sun Mar 19, 2023 9:34 am

bola_dor wrote: ↑Sat Mar 18, 2023 10:25 pm Output channel levels are about 4v.. isn't that too high vor a VGA?

If "output channel levels are about 4V" means RGB signals: Much too high. Did you forget the output resistors? Together with the termination resistors inside the monitor, they scale down the output voltage. Or did you measure at the wrong point?

If "output channel levels are about 4V" means only sync signals: Probably okay.

Still, your problem looks more input related to me, as you seem to get a stable "blue srceen" display. Maybe wrong circuit built, wrong resistor values, or you have damaged your module already. I'm not sure those tinkering problems should be discussed in such a length here, as nobody else has them. A seperate thread might be better, so the actual infos about the QL Pico VGA do not go down in all these posts.

Resistors are all in place. Probably you are right about the measure point at the output as I mesured everywhere while taking photos and didn't take note, I'll review that.

You are so right about the need of new thread.!!
I am sorry abut messing this "general" thread. I'll open a new one at the hardware thread. I wonder if a mod can move this...

Hello!
I am in the process of making this adapter and I have noticed that in the early version there are two 100 ohm resistors connected to GP16 and GP17 for the VGA syncs.
In the later versions, the one with the smaller PI, the 100 ohm resistors are missing and the syncs are directly wired to the VGA connector.
Is that correct or do I need to add the two resistors between GP16,GP17 and the VGA v-sync and h-sync ?
Thanks
Gianni

Hi Gianni,

flyer.gio wrote: ↑Mon Apr 03, 2023 11:00 am In the later versions, the one with the smaller PI, the 100 ohm resistors are missing and the syncs are directly wired to the VGA connector.
Is that correct or do I need to add the two resistors between GP16,GP17 and the VGA v-sync and h-sync ?

It is correct, and tested in several VGA designs. Oliver just called them "fear resistors" agreeing they are not required
Which version with the smaller module are you building, the tiny one, or the more normal sized one?

Peter wrote: ↑Mon Apr 03, 2023 11:11 am Hi Gianni,
.....
It is correct, and tested in several VGA designs. Oliver just called them "fear resistors" agreeing they are not required
Which version with the smaller module are you building, the tiny one, or the more normal sized one?

Hi Peter, thank you for the clarification.
I am designing my own board based on the tiny PI module, it is still on design, not tested yet.

QL-VGA board 3D

I have also added a DB9 socket to the QL side (I will make a proper cable) and two diodes to power the board either from a modded QL or a VESA compliant monitor in addition to the standard usb socket.
I will also build a small 3D printed box.
Here the schematic and the gerber files:

QL-VGA Schematic
QL-VGA Gerber

Gianni

flyer.gio wrote: ↑Mon Apr 03, 2023 3:50 pm ..... two diodes to power the board either from a modded QL or a VESA compliant monitor in addition to the standard usb socket.

Maybe I made a mistake:

Looking closely at the VESA standard, the +5v line is not powered by the monitor, it is an input instead.
In this case the D2 diode can be omitted.

Anyone can confirm my guess?
Thanks

flyer.gio wrote: ↑Mon Apr 03, 2023 7:24 pm Looking closely at the VESA standard, the +5v line is not powered by the monitor, it is an input instead.
In this case the D2 diode can be omitted.

Anyone can confirm my guess?

Confirmed. It could makes sense to modify a cheap monitor to provide 5V output. But in that case, the diode better goes inside the monitor.

Last night, at 1am, I couldn't sleep, so decided to make one of these.

It's not gone well :

Please help, I have 2 basic questions:

1) the the led flash every two seconds if everything is working correctly? (Mine is doing that)

2) without the QL plugged in, does it display a holding screen? (Mine has no signal at all)

On gp16 and GP 17, I'm getting a voltage reading after the resistors 2.9v and 3.3 volts respectively.

I'm using the Pico 2020 and the .5 firmware.

Any help is much appreciated

Update*

On the TV, plugging it in causes the TV screen to go black and all the buttons on the TV stop working!

Further update*

I screwed up the soldering on the VGA end. I grounded pin 4 - wrong.

Think I've got v sync and h sync on the wrong pins too.

Who knew such soldering at 1am could produce such errors!

Alright!!

I found this diagram very helpful, I think the one of the original project is not very clear and seems to show pin 4 as grounded.

Jbizzel wrote: ↑Sat Feb 24, 2024 5:06 am

I found this diagram very helpful, I think the one of the original project is not very clear and seems to show pin 4 as grounded.

Thank for sharing it