Traditional Chinese Practical Multifunctional vision protector: Circuit Design, Parts List & Workshop Prototype Guide

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Multifunctional vision protectorThis kind of vision protector has the following functions and features: (1) The reading or writing distance adopts ultrasonic reflection self-checking method. When the user's face is less than 35cm away from the writing desk, the "distance" light flashes, and at the same time, a rapid "beep, beep, beep" intermittent alarm sounds to remind the user to adjust the sitting posture in time. (2)Learn automatic detection of ambient light. When the light illumination is lower than 100lx stipulated by the National Education Commission, the "light light" flashes and an alarm sounds at the same time to remind the user to turn on the desk lamp or suspend work. (3) Automatic detection of learning time. When the learning time reaches 45 minutes, the "timing light" flashes and an alarm sounds to remind the user to take a break.This vision protector is all designed with CMOS circuits. The circuit is simple and reasonable, and the power consumption is low. The measured quiescent current is not more than 8mA. It is powered by four AA batteries and can generally be used for one semester.Figure 139Circuit principle:The schematic diagram of the circuit is shown in Figure 139. The internal "NOT" gate of IC3 (CD4060) and external components such as R8, R9, C7 and other components form a 3Hz oscillator. The generated square wave signal is sent out from its ⑨ pin, and is sent all the way to one input end of the three "NAND" gates Y1, Y2, Y3; the other is via C2, R 4 differential, and is shaped by the "NOT" gate F1 and then outputs a rectangular narrow pulse with a small duty ratio to control a 40kHz oscillator composed of "NOR" gates H1, H2, R3, R4, and C1. The output signal is buffered by the "NOT" gates F2 and F3 to drive the ultrasonic transmitter B1 to emit a series of 40kHz ultrasonic signals. Compared with the single-ended buffer output (one end of B1 is grounded), this buffer driving method nearly doubles the driving voltage obtained at both ends of B1. B2 is the ultrasonic receiving head, which turns the received ultrasonic signal into an electrical signal. The "NOT" gates F4~F6 and R1 and R2 form a high-gain linear amplifier. The amplification factor AV=-R2/R1. Changing R2 can adjust the amplification factor, thereby changing the detection distance. C3, C4, VD1, and VD2 perform voltage doubling and rectification of the amplified AC signal. If it is within the detection distance, the transistor VT (9012) is turned on, and the collector potential changes from low to high. …

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