| 摘要 |
The receiver has a casing member and a tip is removably attached to the casing member. A transmitter is connected to a battery and the transmitter produces a transmitter signal by periodically connecting a resistance to the battery. Preferably, the transmitter signal has a frequency of about 20 kHz. A sensor may be placed adjacent to, but not in contact with, an electrically conductive member to take advantage of the air capacitance. An electrical field is created between the sensor and the electrically conductive member. Due to the periodical load on the battery, the sensor may sense the transmitter, signal in the DC carrying conductive member. The transmitter signal is passed through an integrated circuit to filter out all frequencies except the desired 20 kHz and a detection signal is sent to the indicator to activate the indicator.
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