Differential anti-interference light control switch

There have been many things these days, and I have not updated my blog. In fact, I haven't compiled any programs recently. I made a circuit or a Analog Circuit for the lights at home during the Spring Festival, there is no such classification here. Put it under C ++.

Although this circuit is relatively simple, I have observed that there seems to be no similar circuit on the Internet. This is an optical control switch. The circuit diagram is as follows:

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This switch has two major features:

Feature 1: It is composed of Schmidt trigger, that is, the switch flip point is at 1/3VCC and 2/3VCC, so there is a return voltage, it can avoid frequent operations when the illumination of common optical control switches changes. For example, when the illumination of an automatic light control lamp falls to the light control switch threshold, the light bulb is switched to light up, and the light bulb emits light, which causes the illumination to rise above the light control switch threshold, in this way, the light control switch acts again to extinguish the light bulb and then light it up ...... We often see the kind of cheap optical control switch to solve this problem is to put the photosensitive sensor photosensitive resistance or photosensitive diode) in the light bulb direct within the range, however, in this way, the lighting range and the photosensitive range are inconsistent, and the actual illumination cannot be reflected. This switch uses a Schmidt trigger consisting of a 555 circuit, which is a good solution to this problem. Schmidt trigger is a voltage control trigger. When the illuminance drops, the photosensitive resistance increases, and the voltage of 2 and 6 feet of 555 drops to less than or equal to 1/3 VCC. 12 V voltage is used here, that is, 4 V), the circuit is flipped, the 3-foot output of 555 is high, and the relay is sucked. On the contrary, when the illumination is increased, the photosensitive resistance is reduced, the circuit will be reversed only when the voltage of 2-foot and 6-foot of 555 is increased to a value greater than or equal to 2/3 VCC, that is, 8 V. Therefore, there is a return voltage of 4 V, the optical control switch has two upper and lower thresholds, which can completely avoid the above switch jitter problem.
Feature 2: a bypass capacitor is connected to the ground at the trigger end of the Schmidt trigger with two or six feet. This capacitor is capable of anti-interference, when the voltage at the lower end of R2 changes due to the variation of illumination, the charge and discharge time of C3 is determined by the size of R2 and C3), so that the voltage at the two and six feet cannot change suddenly, in this way, even if there is an object covering the photosensitive resistance in a short period of time during the day, the relay will not suck together. Similarly, when the relay is sucking at night, there will be a short period of light on the photosensitive resistance, the relay will not be released, that is, anti-interference.

There are basically no special requirements for components in the circuit. The resistance can be 1/8 W metallic film or carbon film resistance. C4 can be used as the ceramic chip capacitor, and C2 can be used as the electrolytic capacitor with a Withstand Voltage of 16 v, you can remove the working indicator lights composed of R4 and D2. The output current of the 555 circuit is relatively large, which can directly push small relays such as 4098, or one-way or two-way thyristor. RV1 can adjust the operation threshold of the optical control switch, select a light resistance with a dark resistance greater than 1 M and a bright resistance less than 10 K.

The value shown in the figure is the tested value, which can work well. The return voltage variation time is about 4 s, that is to say, the change of the two thresholds of the optical control switch requires the illumination to be above or below the threshold for more than 4 s, so the relay will act, so it can resist interference with the pulse width less than 4s.

This circuit is suitable for controlling the prefix of the lantern lights in the Spring Festival family. It is automatically extinguished during the day and automatically lit at night. It does not need to be plugged in or plugged in to the power source every morning, and does not extinguish the lantern lights because of indoor lighting at night, it will not be mistaken for human activity to block light or outdoor fireworks.

Because the circuit is relatively simple, there is no need to corrode the printed circuit board, directly use the experiment board holes) on the right, the overall cost of the circuit is 3-5 yuan.

The circuit is a micro-power consumption. The power supply uses Capacitor Voltage Drop, full-bridge rectification, and zoneer diode voltage regulation. It is not shown here. The detailed calculation of the capacitor pressure drop internal resistance is not an infinitely large constant source ), I will explain it in detail in the next blog.

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