Simple yet efficient bidirectional CMOS<->TTL level matching circuit. It enables using two diffrent logical ONE levels in one single circuit. I used it to match logical ONE level of AVR MCU to that of HC05 bluetooth module while building UART based project. I used two identical circuits for TxD and RxD pins on both chips.
REMARK: In order to emulate transmission of logical 1 and 0 sequence one switch at a time shall remain closed (TxD) while other shall be open (RxD).
