The hottest laser barrier system uses audio detect

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The laser barrier system uses audio detection

in the laser barrier system, the receiving circuit generally realizes the purpose of detection through the signal amplitude. This configuration produces a complex circuit with many components, including amplifiers, filters, and threshold detectors. But you can build a simpler circuit that can detect the signal frequency through the audio detector

the laser barrier consists of a transmitter and a receiver. The transmitter is based on LM555 timer and can work in various modes. It drives the laser diode with frequency square wave F0. The receiving circuit in Figure 1 captures the optical signal through the bpw77 phototransistor (Q1), and then Q2 converts the collector voltage of Q1 into a square wave. This step is necessary due to the frequency response of Q1

in this circuit, detection is independent of amplitude. The LM567 audio detector consists of a class I phase comparator and a voltage controlled oscillator. It is better to pay more attention to the control system and sheet metal technology. When the signal frequency on the input port (pin 3) is within the range of F0 (bw/2), the audio detector will measure different materials and produce a logic zero state on its output port (pin 8). The central frequency f0 and the detection bandwidth BW perform the function of circuit parameters

the center frequency is:

in the circuit, F0 is set to 10 kHz and is well tuned by potentiometer R7. B electro-hydraulic servo universal testing machine is used for static testing of different materials, and W is set at 1.2 kHz. The value of the central frequency is limited by the speed of the phototransistor, while BW is defined by a system response time requirement. C2 and C3 set the bandwidth detection to 12% of F0. Np0 capacitors, such as a polyester type, are used because of their stability over a wide temperature range. The locking time of the audio detector is in the range of 1 to 10 cycles of the central frequency, so the maximum response time is 1ms. Q3 drives led D1 to display the barrier status

optical path is crucial for correct operation. As shown in Figure 2, the lens focuses the emitted beam (a) and pushes the calibration process (b). The lens expands the effective area of the photoelectric crystal that can be used for landfill and other treatment to the maximum (c). This barrier can be used to accurately detect a point that interrupts the optical path. This can be used to detect a small object in an industrial environment, or to detect high-speed movement in a race

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