BOM list:

https://www.digikey.com/en/mylists/list/GWWB9UOM7Q

https://www.aliexpress.com/item/32821797678.html

Smart Solution for a Multisync Video Switch for Atari ST/STE

• Atari DIN13 to VGA
• 3.5mm A/V jack connector
• RCA plugs for audio and composite, adjusted for larger plugs
• Automatic resolution detection
• Buffered H- & V-syncs
• Vivid colors

Instructions:

1. Connect the adapter to the Atari.
2. Power on the computer.
3. Press the button for less than 2 seconds to switch modes.
4. Press the button for more than 2 seconds to save the current video mode as the default for cold boot.

Compatibility:

• BenQ LCD Monitor G2420HD (ET-0027-B) October 2009 Rev. 00-132-BA [VGA]
• MITSUBISHI LCD Monitor RDT1955 [VGA]
• UGREEN 11614 VGA Extension Cable [183 cm]

Note: This is NOT a scan doubler.

It fixes the flicker but keeps the original scan frequency unchanged.

Anyhow the adaptor works when connected to 15KHz video monitors such as BenQ, etc. http://15khz.wikidot.com/ https://15khz.miraheze.org/wiki/Main_Page

Atari STs without an RF modulator only have composite sync. The adapter cannot provide CVBS.

VGA cable is suggested to fit an EMI / RF noise filter (toroid/ferrite) on each end.

Additional Requirement: You need an Arduino UNO to flash the ATTINY correctly or to upload the HEX file.