Features: 4 channel relay output (a normally open, normally closed). 4 channel optical coupling isolation. 4 relay closed the LED light. Circular DC interface, and DC terminal interface. Convenient power connection (12 v power supply voltage). 4 channel input interface. A power indicator light. A user LED light. Specifications: LED light: Yes Power supply voltage: 12V Channel: 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: 1pc Weight: 85g Serial assistant operation instructions: Below are the 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. 1 relay open: 01 06 00 01 02 01 18 aa No. 3 relay close: 01 06 00 01 03 00 d8 fa No. 1 relay open: 01 06 00 01 03 01 19 3a No. 4 relay close: 01 06 00 01 04 00 da ca No. 1 relay open: 01 06 00 01 04 01 1b 0a All put out: 01 06 00 01 00 00 d8 0a All light: 01 06 00 01 ff ff d9 ba Package Included: 1 x 4 Channel Relay Module Note: Please allow 1-3cm differs due to manual measurement. Due to the differe nt display and different light , the picture may not reflect the actual color of the item. Thanks for your understanding. .