Controlling devices over serial (RS-232)¶

Home Assistant Connect AUX-2 has two RS-232 serial ports, Port 1 and Port 2, each on a 3.5 mm jack. Use them to control TVs, AV receivers, projectors, UPS units, climate controllers, and Modbus-capable devices. For signal levels, see Specifications.

Prerequisites¶

• Connect AUX-2 set up in Home Assistant through the ESPHome integration. See Set up Home Assistant Connect AUX-2. Each serial port then appears in Home Assistant as a serial proxy.
• A Home Assistant integration for your device that supports serial proxies. See Check device compatibility.
• A cable from the 3.5 mm jack to your device's serial port. See Cabling and adapters.

Connect your device¶

1. Connect the serial port of your device to RS-232 Port 1 or Port 2.
2. Set the TX/RX switch for that port if your device needs a specific position. Samsung TVs need X, the factory setting. LG TVs need II.
3. In Home Assistant, add the integration for your device, for example Denon, LG, or Samsung.
4. During setup, select the Connect AUX-2 port from the list of serial ports.

If your device doesn't respond, try the other TX/RX switch position.

Check device compatibility¶

Find the integration for your device in Home Assistant's list of serial-controlled integrations, then add it. Integrations that support serial proxies let you pick the Connect AUX-2 port from a list during setup.

Examples of integrations that support serial proxies:

• Denon RS-232, for Denon receivers
• LG TV via Serial, for LG TVs. Set the TX/RX switch for the port you use to II.
• Samsung TV via ExLink, for Samsung TVs. Set the TX/RX switch for the port you use to X, the factory setting.

Community integrations¶

Community integrations are made and maintained by their developers, outside Home Assistant. Community integrations for serial devices:

• Nuvo multi-zone amp
• 12-zone amp + SiriusXM tuner
• NAD T755 / T757 receivers
• BenQ projector
• Arcam hi-fi
• Thessla Green AirPack ventilation

Cabling and adapters¶

Many devices need a converter cable from the 3.5 mm jack to the device's connector, for example DB9, RJ45, RJ9, mini-DIN, or terminal.

Use a cable with a 3-conductor (TRS, stereo) 3.5 mm plug. The sleeve is ground, and the tip and ring carry transmit and receive. A mono (TS) plug has only two contacts and can't carry all three. If the serial connection doesn't work, see The TX/RX switch.

Common connections are a DB9 serial port, usually labeled RS-232C on AV receivers and projectors, or a 3.5 mm serial jack on TVs. Samsung labels the 3.5 mm jack EX-LINK. Other brands label it SERVICE or RS-232C.

To connect to a DB9 serial port, use a 3.5 mm to DB9 serial adapter cable such as the Legrand 3.5 mm to DB9 RS-232 adapter cable. Check that the DB9 end has the correct gender for your device.

To connect a device that uses RS-485, add an RS-232 to RS-485 adapter. This adapter, combined with the DB9 cable above, has been used to connect Modbus devices.

For RS-485 without an inline adapter, you can also use a USB-to-serial dongle in the USB-A port. See Using a USB-to-serial dongle.

The TX/RX switch¶

Pin assignment varies between devices. Each serial port has a switch on the underside of Connect AUX-2 that swaps the transmit and receive lines. If your device doesn't respond, try the other switch position.

The switches are labeled RS-232 TX/RX Swap, and numbered 1 and 2 to match the ports. Each switch has two positions:

• X (crossover): transmit and receive are swapped. Both switches are set to this position at the factory.
• II (straight-through): transmit and receive are passed straight through.

Modbus¶

To connect a Modbus device over RS-485, such as a solar inverter, see Using Connect AUX-2 with Modbus devices.