Automatic dimming curtain circuit

Automatic "dimming curtains" can automatically adjust indoor lighting and are easy to use. The circuit is shown below. Photodiode D and R1, R4, R5 form a balanced bridge. When the light is appropriate, the potentials of points A and B are the same. Both are 1/2EC, and the potentials of pins 3 and 5 at the output terminals of the two KD28 operational amplifiers are also the same. The motor M does not rotate and the curtains remain in their original state. When the outdoor light increases, the indoor light also increases, the internal resistance of the photosensitive diode becomes smaller, the potential of point A rises, the potential of pin 3 of the KD28 output terminal increases, the potential of pin 5 drops, the motor M rotates forward, and the curtain slowly closes until the indoor light weakens, and the resistance of D rises until the bridge is rebalanced. On the contrary, when the light weakens, the motor M reverses and the curtains slowly open. C1 and R6 act as a delay, which can slow down the control process and avoid repeated starting of the motor due to wind accidentally blowing open the curtains. The intensity of indoor light can be divided into three levels: strong, medium and weak. At night, even if the lights are turned on, the indoor lighting cannot meet the weak level requirements and the curtains will all be opened. If you need to close the curtains, you can turn the switch S to the "night" position. At this time, the potential at point A is always higher than the potential at point B, the motor rotates forward, and the curtains are closed. In addition, when the motor is in its two extreme positions (the curtain is fully open or fully closed), there will still be current. For this purpose, an extreme position self-stop switch must be installed, which is completed by contact point J and button AN. When the motor reaches an extreme position, J is disconnected and the power supply is cut off. When re-enabling, press AN, the circuit is connected and the curtain exits the extreme position, J is restored, and the control circuit can control normally again. The control circuit and battery can be installed in a small box and placed on the wall at a convenient location. Care should be taken to keep the photodiode at the top of the box and avoid direct light exposure. Since the extreme position self-stop switch is not difficult to design and install by yourself, it is omitted here.