Using an HDMI cable for rs232 isn't a problem. A cable is a cable is a cable. As long as you are sure it won't be plugged into an HDMI device by mistake (typically not a problem in one off hobby projects). And length may be an issue, as forgiving as rs232 is. A few feet isn't a problem though.
Making your own adapters is the only practical solution you have. Get a db9 dongle and a HDMI connector. If wiring small pins is an issue, there are prewired db9 pigtails and something like this
The second adapter would be HDMI to a 3.5mm Jack or pigtail.
Answer from Passerby on Stack ExchangeAmazon
amazon.com › db9-hdmi › s
Amazon.com: Db9 To Hdmi
Check each product page for other buying options. Price and other details may vary based on product size and color · SABRENT USB 2.0 to Serial (9 Pin) DB 9 RS 232 Converter Cable, Prolific Chipset, HEXNUTS, [Windows 11/10/8.1/8/7/VISTA/XP, Mac OS X 10.6 and Above] 2.5 Feet (CB-DB9P) · DTECH ...
Walmart
walmart.com › electronics
9 Pin Hdmi Adapter
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Alibaba
alibaba.com › showroom › db9-to-hdmi.html
Wholesale DB9 to HDMI Retractable Spring Cable Design | Alibaba.com
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us.ugreen.com › pages › download
Downloads – UGREEN US
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Reddit
reddit.com › r/computers › 9-pin vga to hdmi help
r/computers on Reddit: 9-Pin VGA to HDMI Help
April 15, 2024 - Also, VGA is analog, HDMI is digital, so these cables are very rare.
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ebay.com › shop › db9-to-hdmi
DB9 to Hdmi | eBay
2m Black DB9 RS232 Serial Extension Cable - Reliable Male to Female Connection ... AT SV0po n6Ksore d0A 5 · 1PC Four-Generation Lens HDCI to HDMI+DB9 Compatible RS232 Adapter Cable
Ubuy
ubuy.co.in › home page › new hdmi to db9 serial vga rs232 9-pin adapter cable lead. getwiredusa
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AliExpress
aliexpress.com › w › wholesale-db9-to-hdmi-cable.html
DB9 to HDMI Cable
We cannot provide a description for this page right now
AliExpress
aliexpress.com › w › wholesale-db9-to-hdmi.html
Db9 to hdmi-AliExpress
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Target
target.com › p › unique-bargains-computer-db9-male-female-solder-type-9-pin-adapter-d-sub-connector-15-pairs › - › A-1011133171
Unique Bargains Computer DB9 Male Female Solder Type 9 Pin Adapter D-SUB Connector 15 Pairs : Target
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Naviks
naviks.com › i-24075781-2005-2011-aston-martin-db9hdmi-video-interface.html
2005 - 2011 Aston Martin DB9 HDMI Video Interface
Video inputs (HDMI, AV1) are designed for any HDMI or composite video source (few examples below): ***Sold separately*** -Front view camera -DVD Player -Media Player -Game Consoles -PC’s -Smartphones / Tablets (Depending on the device that will be used an HDMI Adapter is required and sold separately) -Fire Stick -Roku Stick -Apple TV Music & Video playback from Smartphones / Tablets can be achieved with either an HDMI Adapter depending on the device that will be used. HDMI video interface produces only video. Audio from the video source must be routed to the vehicle's OEM 3.5 mm AUX Audio input.
Daraz
daraz.com.bd › tag › db9-to-hdmi
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Micro Connectors
microconnectors.com › db9-male-to-hd15-male-vga-adapter
DB9 Male to HD15 Male (VGA) Adapter - Micro Connectors, Inc.
April 30, 2026 - DB9 Male to HD15 Male VGA Adapter – Connect legacy devices, monitors, and KVM switches with a durable 9-pin to 15-pin VGA connector.
Central Computers
centralcomputer.com › all products › cables › video cables › hdmi vga cables › hdmi male to vga female 9in black cable with audio
HDMI Male to VGA Female 9in Black Cable with Audio
HDMI Male to VGA Female 9in Black Cable with Audio
HDMI Male to VGA Female Adapter Cable, provides a convenient and cost-effective solution for connecting your HDMI source device to VGA monitors or projectors.
Price $9.95
Radioshack
radioshack.com
RadioShack® Official Website | Shop Now | Powering Technology
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Computer Cable Store
computercablestore.com › audio / video › audio / video adapters › vga / svga adapters › vga adapter - db9 male to hd15 female
VGA Adapter - DB9 Male to HD15 Female | Computer Cable Store
VGA Adapter - DB9 Male to HD15 Female
Description · This VGA Adapter offers you the ability to connect a Multi-sync Monitor with a DB9 port to a VGA graphics card without having to buy a new cable. As with all of our products, this VGA Adapter rates high in performance while still being cost effective. · VGA Adapter - DB9 to HD15 · Connectors: Male DB9 to Female HD15 · Designed to connect a multi-sync monitor to a VGA graphics card
Price $2.87
Dtech
dtechelectronics.com › converter-series_c3_2
HDMI Video Converters,VGA To HDMI Converters,AV To HDMI Converters
Tags : hdmi vga converter hdmi to vga converter hdmi to vga converter adapter · Full Speed USB to DB9 Serial Convertor Cable Gold Plated RS232 Serial Interface DB9 1Mbps 1.8M USB to RS232 DB25 Convertor
Reddit
reddit.com › r › QSYS
Qsc Q-sys Community
February 3, 2018 - How can I go about creating a custom IR Driver? I need to control an Episode EA-MINI-5.1D-200 via IR and it's not currently in the list of devices in the IR Driver component. I have the IR hex codes from the published control guide but can't figure out how to create the driver.