An interface circuit electronically connects a processor and a card reader. The interface circuit includes a clock circuit, a reset circuit, and an I/O circuit. The clock circuit may transmit a clock signal transmitted from the processor to the card reader, and includes a first bipolar junction transistor (BJT). The reset circuit may transmit a reset signal transmitted from the processor to the card reader, and includes a second BJT. The I/O circuit may transmit data transmitted from the processor to the card reader, and includes a third BJT and a fourth BJT.