RS-232 Control for AV Devices

RS-232 is a standard for serial communication commonly used in AV systems to control TVs, projectors, PTZ cameras, and other devices. It allows precise, reliable, and bi-directional communication between a controller (e.g., a computer, control system, or automation device) and the target device over a physical cable.

Why Use RS-232?

Reliability: Unlike IR, RS-232 commands are less prone to interference.
Bi-Directional Communication: Devices can send feedback to the controller (e.g., status reports).
Customizable: Commands can be tailored for specific functions.
Long Cable Runs: RS-232 can transmit data over longer distances compared to other control methods.

How RS-232 Works

Cable Connection: RS-232 typically uses a 9-pin DB9 connector, though some devices use a 3.5mm TRS jack or terminal block.
Signal Protocol: Communication is based on a set baud rate (e.g., 9600 bps), parity, data bits, and stop bits. Typical settings are:
- Baud Rate: 9600
- Data Bits: 8
- Parity: None
- Stop Bits: 1
- Flow Control: None
Command Format: Commands are sent as strings of text or hexadecimal bytes.

Common RS-232 Commands

RS-232 commands vary by device and manufacturer but typically follow a standard structure. Below are common commands for TVs, projectors, and PTZ cameras.

1. Power Control

Power On:
Command: PON or POWR 1
Example (HEX): 0x50 0x4F 0x4E
Power Off:
Command: POF or POWR 0
Example (HEX): 0x50 0x4F 0x46

2. Input Selection

Switch to HDMI 1:
Command: INPUT HDMI1 or INPT 1
Example (HEX): 0x49 0x4E 0x50 0x54 0x31
Switch to VGA:
Command: INPUT VGA or INPT 3

3. Volume Control

Volume Up:
Command: VOLU
Example (HEX): 0x56 0x4F 0x4C 0x55
Volume Down:
Command: VOLD
Set Volume Level:
Command: VOL 50 (sets volume to 50%).

4. Mute Control

Mute On:
Command: MUTE 1 or MUT ON
Example (HEX): 0x4D 0x55 0x54 0x45 0x20 0x31
Mute Off:
Command: MUTE 0 or MUT OFF

5. Status Requests

Power Status:
Command: QPW (Query Power Status)
Response: POWR 1 (on) or POWR 0 (off)
Input Status:
Command: QIN
Response: HDMI1, VGA, etc.

6. Projector-Specific Commands

Lamp On:
Command: LAMP ON
Lamp Off:
Command: LAMP OFF
Check Lamp Hours:
Command: LAMP?
Response: LAMP=1500 (hours used).
Shutter Open/Close:
Command: SHUT 1 (open) / SHUT 0 (close).

7. PTZ Camera Commands

Pan/Tilt Control:
- Pan Left: PAN LEFT
- Pan Right: PAN RIGHT
- Tilt Up: TILT UP
- Tilt Down: TILT DOWN
  Example (HEX): 0x50 0x41 0x4E 0x20 0x4C 0x45 0x46 0x54
Zoom Control:
- Zoom In: ZOOM IN
- Zoom Out: ZOOM OUT
Set Preset:
Command: PRESET 1 (sets current position as preset 1).
Recall Preset:
Command: GOTO 1.

8. Device Reboot

Restart Device:
Command: REBOOT or RST

Setting Up RS-232 Control

Step 1: Establish a Physical Connection

Connect the controller to the device using an RS-232 cable. Match the pins:
- Tx (Transmit) on the controller to Rx (Receive) on the device.
- Rx (Receive) on the controller to Tx (Transmit) on the device.
- Ground (GND) to GND.

Step 2: Configure Communication Parameters

Use the manufacturer’s manual to configure the baud rate, data bits, parity, and stop bits in your controller software or terminal emulator (e.g., PuTTY, Tera Term).

Step 3: Send Commands

Open a terminal emulator or control software.
Input the command and press “Enter” or send it as raw bytes in HEX.

Step 4: Test Communication

Begin with simple queries like power status (QPW) to confirm the connection.

Common Tools for RS-232 Control

Terminal Emulators: PuTTY, Tera Term, or RealTerm.
Control Systems: Crestron, AMX, Extron, or Control4.
Debugging Tools: RS-232 protocol analyzers or USB-to-RS-232 adapters.

Best Practices

Read the Manual: Each device has unique commands—consult its RS-232 guide.
Test Incrementally: Verify communication with basic commands before moving to advanced setups.
Cable Length: RS-232 works best under 50 feet; for longer distances, use RS-422/485 or repeaters.
Document Configurations: Record settings like baud rate and parity for future reference.

Brooks AV