Hands-free Passive Keyless Entry (PKE) is quickly becoming mainstream in automotive remote keyless entry. In hands-free PKE applications, a base unit inside a vehicle transmits a Low-Frequency (LF) command that locates a transponder in the vehicle owner’s possession. The transponder then responds to the base unit, which unlocks the car doors. The most probable source of PKE operation failure is due to a weak input signal level at the transponder. Therefore, for a reliable hands-free PKE application, it is necessary to make the input signal strong enough in any condition within the desired communication range.


The PIC16F639 is a microcontroller (MCU) with a three-channel analog front-end. Because of its easy-to-use features, the device can be used for various smart low-frequency sensing and bidirectional communication applications. This application note provides design circuit examples of the smart PKE transponder using the PIC16F639 MCU.