How to suppress RS232 communication interference in HMI (Human Machine Delivery) systems?

To suppress interference in HMI RS232 communication, it's necessary to address its single-ended transmission and large voltage swing characteristics. RS232 signal lines are susceptible to common-mode interference. Suppression measures include: connecting ferrite beads, such as PBZ1608E102Z0T, in series on the TX, RX, and control signal lines to absorb high-frequency noise; and connecting a TVS diode array, such as SMBJ12CA, in parallel between the line and ground to suppress transient overvoltage and ESD. For long communication distances or harsh environments, it is recommended to use isolated RS232 chips, achieving electrical isolation through optocouplers or magnetic couplings. In PCB layout, the RS232 level conversion chip should be placed close to the interface connector, and the surrounding protective filtering components should be compactly arranged.

RS232 signal lines should be as short as possible, avoiding parallel routing with power lines or other high-speed signal lines. The ground of the interface circuit should be connected to the digital main ground at a single point via a ferrite bead, or a separate interface ground should be provided. The metal housing of the connector must be reliably connected to the device chassis. On the software side, timeout retransmission and verification mechanisms for the communication protocol can be added. To address power supply noise generated by the RS232 chip, decoupling must be strengthened on its power supply pins. By employing devices such as ferrite beads and TVS diodes from Etymotic, combined with isolation and proper layout, interference in RS232 communication can be effectively suppressed, ensuring the stability of data transmission.