Vision protector II

Circuit Operation Principle The vision protector circuit consists of a power supply circuit, an ultrasonic transmission circuit, an ultrasonic reception control circuit, a timer control circuit, an ambient light detection circuit, and an acousto-optic alarm circuit, as shown in Figure 9-60.

The power circuit is composed of a power switch S, a battery GB, a current limiting resistor R1, and a filter capacitor Cl.
The ultrasonic transmitting circuit is composed of a time base integrated circuit IC4, resistors Rlg, R2O, a capacitor Cl2, and an ultrasonic generator B2.
The ultrasonic receiving control circuit is composed of an ultrasonic receiver B1, resistors R2-R6, capacitors C2-C4, and transistors V1-V3.
The timer control circuit is composed of timer integrated circuit IC3, potentiometer R-tooth, resistor R9, RlO, Rl5-Rl9, capacitor C5, C7, C8, ClO, C11, NAND gate integrated circuit IC2 (D5-D8) D7, D8 and transistors V4, V5.
The ambient light detecting circuit is composed of a photoresistor RG, a capacitor C6, a resistor R8 and a potentiometer RP1.
The sound and light alarm circuit consists of NAND gate integrated circuit ICl (Dl-D4), D5-D7 inside IC2, resistor R7, Rll-R14, capacitor C9, diode VD3-VD5, LED VLl-VL3 and buzzer HA composition.
After the power switch S is turned on, the battery GB provides a 6V DC working voltage for the whole machine.
The timer control circuit oscillates after power-on, and outputs an ultra-low frequency oscillation signal from pin 9 of IC3. The signal is inverted by NAND gate D8 and amplified by V5 and V4, and then used as an ultrasonic transmission circuit (oscillation frequency is 38-4OkHz). The circuit modulates the pulse signal so that B2 emits an ultrasonic signal.
Bl receives the ultrasonic signal transmitted by B2 and converts it into an electrical signal, which is amplified by V1, V2, VD1 and VD2 and is applied to the base of V3. When the distance between the user's head and the writing surface is greater than 35 cm, V3 is not turned on, and the NAND gate D1 outputs a low level, and the sound and light alarm circuit does not work; if the user's head and the writing surface are between When the distance is less than 35cm, V3 is saturated and turned on, so that Dl outputs ultra-low frequency pulse signal, VL2 flashes, and the audio oscillator composed of non-l gates D3, D4 and R11, C9 oscillates, and HA emits "drop, feed" The beeping alarm sounds to remind the user to pay attention to the sitting posture and adjust the reading and writing distance in time.
When ambient light is suitable for reading and writing, RG is in a low-resistance state, NAND gate D5 outputs a high level, D6 outputs a low level, VLl does not emit light, and HA does not sound. When the ambient light is weak and lower than the read/write requirement, the resistance of RG increases, so that the NAND and D6 outputs a high level, the audio oscillator oscillates, and the HA emits a beep; at the same time, the non-"D5 output" The ultra-low frequency pulse signal causes VLl to flash.
When the timing time (45min) has not expired, IC3's 3 pin outputs a low level, VL3 does not emit light, and VD5 is in an off state, which has no effect on the audio oscillator. When the timing time is over, IC3's 3 pin outputs a high level, so that VL3 lights up, VD5 turns on, and HA emits a long beep, reminding the user to take a break.
Adjusting the resistance of RPl can change the sensitivity of the ambient light detection circuit.
Adjusting the resistance of RP2 can change the length of the timing.
Component selection
Rl-R2O uses 1/4W metal film resistor or carbon film resistor.
RPl and Rm use small synthetic carbon film potentiometers.
RG uses a photoresistor with a light resistance of less than 2kΩ and a resistance greater than 5OOkΩ.
Cl uses aluminum electrolytic capacitors with a withstand voltage of lOV; C2, C3, C5-C9 and C11 use monolithic capacitors or polyester capacitors; C4, ClO and Cl2 use high-frequency ceramic capacitors or glass glaze capacitors.
VDl-VD5 selects 1N4148 type silicon switch diode for use.
VLl-VL3 selects high brightness LED of φ5mm.
V1, V2 and V4 select S9014 type silicon NPN transistor; V3 and V5 select S9012 type silicon PNP transistor.
IC1 and IC2 select CD401l or CC4011 type four NAND gate integrated circuits; IC3 selects CD4060 or MCl4060 type timer integrated circuit; IC4 selects NE555 type time base integrated circuit.
Bl selects UCM-40R ultrasonic receiver; B2 selects UCM-40T ultrasonic transmitter.
HA uses a piezoelectric buzzer.
S uses a small toggle power switch.
GB uses 4 sections of the 5th or 7th battery in series.