The fingerprint scanner shown in the figure above is from ADH-TECH and it communicates at TTL levels serially.The module itself does all of the heavy lifting behind reading and identifying the fingerprints with an on-board optical sensor and 32-bit CPU. The module can only store up to 20 different fingerprints but is capable of 360° fingerprint recognition and download and upload templates using serial interface. The module is small and easy to mount using two mounting tabs on the side of the sensor. The on-board JST-SH connector has four signals: Vcc, GND, Tx, Rx.