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  • Passive keyless entry- transponder circuit

  • Created: Aug 14, 2014

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Passive Keyless entry-Transponder

Passive Keyless Entry (PKE) transponder allows one to gain access by simply having a valid transponder in their possession. One prominent application of this schematic is in vehicle access wherein the person may be able to have an access to the vehicle without the need of pressing a button but only by having the valid transponder with them.

Hands-free PKE applications require bidirectional communication between the base station and transponder units. The base unit inside the vehicle transmits a Low-Frequency (LF) command that searches for a transponder in the field. Once located, the transponder in the vehicle owner’s possession then automatically responds to the base unit. The base unit then unlocks the car doors, if a valid authentication response is received. Typical PKE applications adhere to the electromagnetic field radiation rules that are mandated by the government agencies in relation to the maximum power transmitted by the transponder and base station.

The PIC16F639 has a digital MCU section (PIC16F639 core) and an analog front-end (AFE) section. The device can be used for various low-frequency sensing and bidirectional smart communication applications. The base station unit transmits a 125 kHz command to search for a valid transponder in the field. The PKE transponder sends back a response if the received command is valid. The PIC16F639 device has high analog input sensitivity (up to 1mVPP) and three antenna connection pins. By connecting three antennas that are positioned to x, y and z directions, the transponder can pick up signals from any direction at any given time.



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