Electrically Isolated RS232 Adapter

This circuit represents an interface converter between the UART pins of a microcontroller (with TTL levels) and a ‘standardised’ RS232 port with symmetric ±15-V levels. In contrast to the commonly used IC solutions such as the MAX232, it also provides electrical isolation between the two sides of the converter. This interface converter inverts the signals, so the usual inverters on the microcontroller side can (and must!) be omitted.In most cases, the data lines RxD and TxD are all we need for communications with microcontroller systems. Fortunately, handshake signals are very seldom exchanged. The related RS232 leads are thus interconnected in such a manner that communications can take place without any problems.