RS232 Relay Board 12V 4-Channel Relay Module, PC Controlled DB9 Serial, Momentary/Toggle/Interlock

Product Name: DC 12V 4 Channel RS232 Relay Board PC USB UART DB9 Remote Control Switch for Smart Home Garage door Car alarm Farm Motor. Overview This compact 4 channel RS232 relay board provides reliable, serial-controlled switching for DC 12V devices and external AC or DC loads. It is designed for remote control, automation, and integration with PLC or PC serial ports. The module offers clear status feedback, low standby current, and a simple UART protocol for easy integration into automation projects. Key features and specifications - Relay channels: 4 independent SPDT relays with NO COM NC contacts. - Power input: DC 12V nominal, operating range 8.5 to 13.5V. - Current consumption: standby (all relays closed) 18 mA; 1 relay open 50 mA; 2 relays open 81 mA; 3 relays open 110 mA; 4 relays open 140 mA. - Indicators: Power LED plus individual LED indicators for each relay output for visible status. - Communication: UART serial protocol via RS232. Default settings: baud rate 9600 kbps, 8 data bits, 1 stop bit, no parity. Two-way data transmission, each data frame contains eight bytes. - Physical: 90 mm x 47 mm x 19 mm, weight 62 g. - PCB printing correction: the printed silkscreen is incorrect; the correct labeling is NO4 COM4 NC4 NO3 COM3 NC3 NO2 COM2 NC2 NO1 COM1 NC1. - Package included: 1 x DC 12V 4Ch RS232 Relay Board. Why customers need this board - Simple serial control: Use standard RS232 UART commands from a PC, PLC, or USB to RS232 adapter to switch loads without additional I O expansion hardware. - Clear status reporting: LED indicators and two-way UART frames provide immediate feedback for reliable automation and remote monitoring. - Low standby power: Minimal idle current makes it suitable for always-on systems and battery-backed applications. - Versatile load support: Drive DC 12V devices directly, and control external DC or AC loads via the relay contacts for motors, lights, alarms, and valves. Control commands and responses 1. Read status (read relay on or off) 55 56 00 00 00 00 00 AB 2. Relay open (COM connects to NO) Channel 1 55 56 00 00 00 01 01 AD Channel 2 55 56 00 00 00 02 01 AE Channel 3 55 56 00 00 00 03 01 AF Channel 4 55 56 00 00 00 04 01 B0 3. Relay close (COM disconnects from NO and connects to NC) Channel 1 55 56 00 00 00 01 02 AE Channel 2 55 56 00 00 00 02 02 AF Channel 3 55 56 00 00 00 03 02 B0 Channel 4 55 56 00 00 00 04 02 B1 4. Relay toggle (reverse relay state) Channel 1 55 56 00 00 00 01 03 AF Channel 2 55 56 00 00 00 02 03 B0 Channel 3 55 56 00 00 00 03 03 B1 Channel 4 55 56 00 00 00 04 03 B2 5. Relay momentary (COM connects to NO, then disconnects after 200 ms) Channel 1 55 56 00 00 00 01 04 B0 Channel 2 55 56 00 00 00 02 04 B1 Channel 3 55 56 00 00 00 03 04 B2 Channel 4