Features: 4 channel relay output (normally open, normally closed). 4 channel optical coupling isolation. 4 relay closed LED indicator. Circular DC interface and DC terminal interface. Convenient power connection with 12V power supply voltage. 4 channel input interface. Power indicator light. User LED indicator. Specifications: LED light: Yes Power supply voltage: 12V Channels: 4 Baud rate: 9600 Microcontroller: STM8S103F3 Reset button: Yes Size: Approx. 7.8 x 7.7 x 1.8cm / 3 x 3 x 0.7inch Quantity: 1 piece Weight: 85g Serial assistant operation instructions: Test instructions for device number 1: No. 1 relay close: 01 06 00 01 01 00 d9 9a No. 1 relay open: 01 06 00 01 01 01 18 5a No. 2 relay close: 01 06 00 01 02 00 d9 6a No. 2 relay open: 01 06 00 01 02 01 18 aa No. 3 relay close: 01 06 00 01 03 00 d8 fa No. 3 relay open: 01 06 00 01 03 01 19 3a No. 4 relay close: 01 06 00 01 04 00 da ca No. 4 relay open: 01 06 00 01 04 01 1b 0a All relays off: 01 06 00 01 00 00 d8 0a All relays on: 01 06 00 01 ff ff d9 ba Package Included: 1 x 4 Channel Relay Module Note: Please allow 1-3cm variation due to manual measurement. Due to different display settings and lighting conditions, the picture may not reflect the actual color of the item. Thank you for your understanding.