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Most TV ports go unnoticed once everything is plugged in — except perhaps HDMI and USB. But for advanced users, the RS-232 serial port can be a powerful tool for fine-tuned home theater and smart device control.

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With some patience and more than a little know-how, you can create a fully automated home entertainment system with timed content, simultaneous broadcasts to multiple rooms, and even diagnostic testing.  

What is an RS-232 serial port, and what does it do?

Take a peek at the back of your TV, and you may see -- among the familiar HDMI and USB connections -- an odd 9-pin port that doesn't match any cable you have in the house (and may look familiar if you used a printer back in the 1990s). This is your TV's RS-232 serial port, normally reserved for connecting professional calibration and diagnostic tools. 

Technicians at the factory or in a repair shop have special testing devices that plug into the RS-232 port to test signal transmission strength, debug software, and check for electrical damage. 

The RS-232 port can also be used in both smart home and commercial settings by enabling you to connect multiple TVs to a single source for custom broadcasts. Whenever you go to a doctor's office or an airport where multiple screens show the same reels of advertisements and safety announcements, you're seeing the RS-232 connection at work. 

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While this port is generally reserved for business use, if you have the money and desire, you can use the RS-232 connection to set up a custom multi-room broadcast system; you can watch the same content in multiple rooms throughout your house in perfect sync, or create custom, curated playlists for your home-based business, kids' playroom, or your next house party.

Which TVs have an RS-232 port?

While many brands include an RS-232 port in smart TV builds, it's usually reserved for the higher-end models. Commercial-grade TVs will also include a connection, as they are specifically designed for use in RS-232 broadcast systems. Some midrange models from more established brands like LG may feature an RS-232 connection, but it's rare to see one on a budget model. 

Using the RS-232 port at home

Using the RS-232 on your TV isn't for the faint of heart or technology-averse. But if you know how to code, setting up an automated video feed is fairly straightforward. You'll need either an RS-232 cable or RS-232-to-Bluetooth adapter and a computer. 

Once you've got your TV connected to your PC or laptop, you can create code protocols for precision timing, to specify the content to include, and to specify where to broadcast your content. 

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Another device you'll need will be a Serial Port/HDMI matrix. This acts as the central hub for your system, connecting your PC, main TV, and satellite screens to a single switch box for an all-in-one control solution. Matrix receivers offer a range of connectivity options, with some supporting up to 32 separate HDMI inputs and outputs for setting up commercial systems. 

However, for home use, an 8x8 HDMI matrix will be more than enough to handle a casual system. Many HDMI matrix boxes also have Ethernet and Wi-Fi connectivity, so you can stream web content from apps like Netflix and HBO Max, as well as YouTube and Twitch. You can also find models that support Dolby and DTS audio passthroughs for custom sound systems to augment your TV speakers or play separate audio. 

Finding the right programming language

Since each system is unique, you'll need to check which programming language your devices use to communicate with one another and process audio and visual signals. These programs are often proprietary and require a fair bit of knowledge to properly modify for your particular setup. 

If you need a jumping-off point, you can find step-by-step coding guides for controlling specific brands and device systems on GitHub; coding languages range from HTML and C# to Python and Java (and everything in between), so you shouldn't have trouble finding a control module that works for you.

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If you're looking to monitor your smart TV's health via the RS-232 port, you can purchase a signal tester for around $20. Many are compatible with Windows, MacOS, and Linux, allowing you to seamlessly integrate your smart TV into your PC setup, no matter which operating system you use. 

An RS-232 tester will check for dead or damaged connector pins, signal strength, and communication between your TV and PC; if any issues arise, you'll get detailed feedback on the problem for fast troubleshooting and solutions.  

Bottom line

If you are into Home Assistant, Crestron, or Roomie Remote, the RS-232 port is a goldmine. It is significantly more reliable than IR blasters (which can be blocked) or CEC (which is notoriously buggy). Just understand that setting up the RS-232 port to handle your automations or other personalized tasks will take time and learning.