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15kHz passthrough CRT protection dongle - sale thread

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I have built a small batch of 15kHz CRT monitor protection passthrough dongles for sale. These are based on @Gambamanís excellent Ultimate VGA-to-SCART design.,160869 They plug into a VGA socket, and pass 15kHz RGBHV as RGBS (C-sync on pin 13). Any video modes with a higher scan rate get blocked.

One dongle is US$50 shipped anywhere outside Australia. Or AU$50 shipped inside Aus.

Can anyone interested please PM me saying you've read and understood this entire post :)

This dongle has three primary uses:
1.   To give CRT arcade monitors some protection.
2.   To generate clean composite sync in certain situations.
3.   As a testing tool to prove a VGA port is/isnít outputting 15kHz.

1.  Most old CRT arcade monitors work at 15kHz and their sync circuitry needs protection from video modes with higher scan rates. (Remembering that arcade monitors were designed to sync to two or three closely-related video modes in their lifetime, not to switch six times whenever you boot up Windows at low res.) Consumer CRTís from the 90ís onwards donít strictly need protecting. Same with PVMís. That said, nothing lasts forever, and the dongle will help you treat their aging electronics a bit more gently.

2.  When a 15kHz video mode is detected, the green LED is lit. The dongle then outputs RGBS via a female DB15HD (VGA) plug, pushing composite sync on pin 13. Most cheap VGA-to-SCART cables will be fine if they also pass 5V from pin 9 (if needed) as will any VGA-to-BNC cable, but you should determine how your setup will work before purchasing.

No c-sync signal is perfect, and operation cannot be guaranteed with any other devices that modify or recreate sync (strippers, positional adjust, signal converters, or any other device without 5V over VGA pin 9) nor with any monitors that have sync issues or interlaced flicker issues. All the PVMís, arcade monitors, and consumer CRTs I own work fine, except the PVM-2730 (which flickers in general, and anyway still works fine at 240p.)

When a video mode with a scan rate above 17kHz or below 15kHz is detected (say, when Windows defaults to 480p sometimes) sync is blocked and the red LED comes on. R, G & B are still passed, so you may see something harmless on screen.

This dongle does nothing to framerate, so if the signal going in was at 50Hz, it will remain at 50Hz (unless blocked). It passes 5V on pin 9, but does not pass EDID, and pin 5 is floating.

3.  The dongle makes an excellent diagnostic tool. With or without a cable you can prove your PC is or isnít outputting video correctly. This would be really handy for anyone jumping into GroovyMAME for the first time. Or anyone with a 15kHz PC connected to windows updates like mine. That said, general support for crt_emudriver should be politely requested in the GM forum, as i don't know everything :)

EDIT: reply #7 contains testing info about compatibility with other devices -,167729.msg1766145.html#msg1766145

Looks like a very useful product.   :cheers:

--- Quote from: buttersoft on June 06, 2023, 09:40:14 pm ---Hope this is ok to post here!

--- End quote ---
I moved the thread to "Retail Vendors" since it is offering "a small batch" of an item for sale.
- Selling 3 or more of an item with the possibility of acquiring/making more for resale ==>"Retail Vendors" sub-forum.
- Selling items that you won't be acquiring/making more of for resale ==> "Buy/Sell/Trade" sub-forum.

I also put a redirect topic in the "Monitors" sub-forum with a link to this thread so people can easily find it in either sub-forum.



Glad you're offering these for sale. Very handy little dongles.

Thanks also for making the LEDs different sizes. Otherwise, people with red-green colour blindness would weep.

Thanks, Scott. I wasn't sure where to post :)

And Zeb, i hadn't thought of the colourblind issue! (I accidentally bought shorter red LED's, i didn't mean to :/) It's not easy modifying the dongles when already built, but I could make new ones with red, green, yellow, blue or white LED's on request.

Is OK, no need to retrofit for me, I'm kinda used to it :D

Yes I am "red-green colourblind", despite designing and building colour space transcoders. It's all maths anyway. FWIW the "blind" part is a misnomer - I still see the colours just fine, is just the way retina cone frequency sensitivities are tweaked.

Some colour shades that are different to most people may look similar to me. OTOH often I see colours or differences where other don't. I see the world slightly differently, but then we all do to some extent.

We have a big green tree with bright red flowers that my wife describes as "outstanding", yet I hardly notice them until I look closely. Stuff like resistor colour-coding is also a nightmare (small as well), I usually have fun guessing then just grab the DMM (like most normal people probably!).

I love your dongle but distinguishing LED colours is hard. Certain things, like old-school red/green/orange LEDs, especially diffused ones, are horrible to distinguish. Guess it doesn't really matter, it is either one or two LEDs on. Colour is irrelevant.

The newer LEDs like the "bright" or "superbright" "clear" ones seem much better (guess it depends on exactly what you get). Many colours to choose from. They can be very bright if run at ~20mA - you can reduce the brightness to suit your needs by using a larger resistor to limit current. 

BTW your dongle works great with GreenAntz! Am testing it as I write. You must use the dongle directly at the video card VGA head though. It won't work attached via a VGA male-male cable, the sync doesn't pass through. Red LED lights up but not the other one (whatever colour it is). Not sure why as all 15 pins are present and accounted for.

I may pull it apart and have another look later :D


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