Vision protector

The visual protector introduced in this example can emit an audible and visual alarm signal when the ambient light is not enough, lower than the reading standard, to remind the user to turn on the light or stop reading and writing in time to protect the vision.
Circuit Operation Principle The vision protector circuit consists of a photometric circuit, an LED flash circuit and an audible cue circuit, as shown in Figure 9-59.

The photometric routing resistor R1, the potentiometer RP and the photodiode VD are composed.
The LED flash circuit is composed of NAND gates D1, D2, resistors R2, R3, capacitor C1, transistor V1 and light-emitting diode VL inside the NAND gate integrated circuit 1C (D1-D4).
The audible cue circuit is composed of NAND gates D3, D4, resistor R4, capacitor C2, transistor V2 and buzzer HA inside the IC.
Turn on the power switch S, the battery GB provides 3V working power for the whole machine.
When the ambient light is strong, the internal resistance of VD is small, the voltage drop across it is small, the oscillator A consisting of D1, D2, R2, Cl and the oscillator consisting of D3, D4, R4, C2 B does not oscillate, V1 and V2 are both in the off state, VL does not emit light, and HA does not sound.
When the ambient light becomes weaker than the normal reading and writing illumination standard, the internal resistance of VD increases, and the voltage drop across it increases, causing both oscillators to oscillate (oscillator A output oscillator signal to oscillator B) Modulation), V1 and V2 are intermittently turned on, VL flashes, and HA emits a "drop, drip" sound with a frequency of about 3 Hz.
Adjusting the resistance of the RP can change the sensitivity of the circuit action.
Component selection
Rl-R4 uses 1/8W metal film resistor or carbon film resistor.
RP uses ultra-small synthetic carbon film potentiometers or variable resistors.
Both Cl and C2 are aluminum electrolytic capacitors with a withstand voltage of 6.3V.
VD uses the 2CU series of photodiodes.
VL selects φ5mm LED.
Both Vl and V2 use S9013 silicon NPN transistors.
IC selects CD401l or CC4011 type four NAND gate integrated circuits.
HA uses a 3V DC electromagnetic buzzer.
GB uses two 5 or 7 batteries.
S uses a small toggle switch.