Counterfeit detection circuit

摘要

A magnetic sensor including a coil for sensing a changing magnetic field developed by paper currency moving past the magnetic sensor. A capacitor forms a tuned circuit with the magnetic sensor coil to pass only those signals lying within a predetermined frequency range. A comparator compares the signals lying within the pass band with a predetermined threshold to determine the presence or absence of genuine currency. The tuned circuit significantly improves the signal to noise ratio of the sensing means and hence, significantly improves the ability to determine the genuineness of the currency. In a second embodiment, the presence of a magnetic field having a field strength above the predetermined threshold is utilized to pass timing pulses for clocking a counter. A decoder gate coupled to the counter indicates the presence of a genuine bill, only after a predetermined count has been reached. A reset circuit is provided for resetting the detecting circuitry immediately after each bill is examined and before examination of the next bill.