A card reader includes a printed circuit board (PCB). The PCB includes a universal serial bus (USB) interface to be connected to an electronic device, a card interface to be connected to a card, a control chip, and a normally-closed switch coupled in a wire connecting a positive differential pin of the USB interface to the control chip. A length of the wire connecting the positive differential pin of the USB interface to the control chip equals to a length of a wire connecting a negative differential pin of the USB interface to the control chip. The normally-closed switch is operable to be switched on or switched off, so as to control the connection between the card and the electronic device.