Electric curtain circuit

working principle

The power transformer B, bridge rectifier and capacitor C1 form a 12V DC power supply. Relays J1, J2 and travel switches K1, K2 form an interlocking power polarity switching circuit.

When the button QA is pressed, the 220V AC power is connected, and the indicator light L is on. Due to the existence of C2, the voltage at both ends of J1 cannot change suddenly, so J2 is first attracted, J2-1 is closed, the circuit is self-protected, J2-2 is disconnected, the circuit is interlocked, J2-3 and J2-4 are closed, the motor is powered on and rotates forward, and the curtain is opened. After the curtain is fully opened, the travel switch K2 is pulled by the pull wire and disconnected, J2 loses power and releases, J2-1 is disconnected, and the entire circuit is powered off and stops working. After the curtain is fully opened, when QA is pressed again, because K2 is disconnected, J2 cannot be attracted, J1 is attracted, J1-1 is closed, the circuit is self-protected, the indicator light L is on, J1-2 is disconnected, the circuit is interlocked, J1-3 and J1-4 are closed, the motor is powered on and reverses, and the curtain is closed. After the curtain is fully closed, the travel switch K1 is pulled by the pull wire and disconnected, J1 loses power and releases, J1-1 is disconnected, and the entire circuit is powered off and stops working.

When the curtain needs to stop at any position, just press button TA during the curtain movement. It should be noted that the opening and closing of the curtain controlled by this circuit is based on the opening start as the priority, that is, as long as the curtain is not fully open, when QA is pressed, the curtain always moves in the opening direction. However, in daily use, the curtain is generally fully open and fully closed in a cycle, so only one button QA can be used to control the opening and closing of the curtain.

Component selection

The motor should be selected according to the texture, size and weight of the curtains. The transformer, rectifier full bridge and relay contact capacity should be selected according to the working current of the selected motor. J1 and J2 should use 12V DC relays with 4 groups of contacts. It is best to use one with a socket. This type of relay is very convenient to connect when used. The travel switch should use a micro switch with a reed. Other components should be selected as marked in the figure.

Experimental comments

The circuit does have the advantages the author mentioned: fewer components and strong feasibility. However, when the author connected and used it according to the diagram, he found that K1 and K2 had a step-forward phenomenon when starting the circuit, which was not as accurate as the author said (K2 was connected before K1, and the curtain moved in the direction of opening).
　The author made the following changes: In the K1 branch, two diodes were connected in series between K1 and J2-2. The author used two 1N4001s (a 50Ω/2W resistor could also be used). This makes the circuit more reliable without affecting the pull-in of J1.