Since most devices that still have this port use TTL voltage levels, the schematic I will show you is compatible with 3.3 V and 5 V levels.įunctional schematic of serial port monitor/sniffer Since most modern devices do not use auxiliary lines, the circuit shown here is able to monitor only a single pair of Rx and Tx lines. The sniffer I will show you here is able to intercept serial communication and disable Tx lines in order to inject its own data. You may use a logic analyzer to check the bitstream and determine its baudrate and if that's present, the next step is to view or record what's being sent over the port. There are times when serial communication needs debugging. Nowadays, mostly Rx and Tx signal lines are used. The serial port is no longer found in its original shape and pinout. The original voltage levels (ranging from -15 to +15 V) have been replaced with platform specific levels (from 0 to 2.5 V, 3.3 V or 5 V). Despite this, the protocol used by RS-232 is still in use today, on various devices, ranging from microcontrollers to embedded systems and even computers. Today, RS-232 has mostly been replaced in personal computers by USB for local communications which allows for faster speeds and is easier to connect and use. Build this versatile, yet simple serial port sniffer to debug and take over communication between two devicesĪ serial port complying with the RS-232 standard was once a standard feature of many types of computers.

Linux serial port sniffer