A diagram of the detector is a simple light relay or detector, triggered by infrared radiation of the led D1. The main application of the device is the control system. In the absence of radiation of diode D1 on the phototransistor Q1, the relay K1 is in a normally open condition. There are various options the design of the device.
It is possible that the phototransistor Q1 is triggered from the reflected beam (as a reflector can be used a mirror) infradead D1. The advantage of this relay is the lack of visible eye radiation . The sensitivity of the device is determined by the parameters D1, Q1, R2, and the design of the device.
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