| 摘要 |
A modulated touch entry system and corresponding method for detecting the presence and location of a member within an irradiated field. A touch entry system and corresponding method are disclosed which utilize modulated pulses of light from light emitters, such as light emitting diodes, which are detected by corresponding light detectors, such as phototransistors. The light emitters and the corresponding light detectors are arranged around a frame to provide an irradiated field. The system utilizes circuitry to precondition a signal from the light detectors prior to analyzing the presence of a "hit"; i.e., the presence of a member within the irradiated field. The circuitry includes a differential amplifier and a programmable amplifier, which consists of a digital to analog converter, a current to voltage converter, and a gain stage, to precondition the signal from the light detectors. The portion of the circuit which detects the modulation of the signal from the light detectors is synchronized with the frequency of the modulation of the light pulses so that it detects the presence or absence of modulated light pulses. A filter portion of the circuit for providing an appropriate output signal is also disclosed, as is a circuit for sampling the ambient light strength and selectively disabling the modulation detection circuit when ambient light strength exceeds a preselected value.
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