Using switch S3 also allows manual control, allowing for curtains to be left only partially open or closed. The circuit controls a motor which is attached to a simple pulley mechanism, to move the curtains. I first started this circuit over 20 years ago and apart from now using metal gears, very little has changed.
Notes:
Automatic Operation
The circuit can be broken down into three main parts; a bistable latch, a timer and a reversing circuit. Toggle switch S3 determines manual or automatic mode. The circuit as shown above is drawn in the automatic position and operation is as follows. The bistable is built around Q1 and Q2 and associated circuitry and controls relay A/2. S1 is used to open the curtains and S2 to close the curtains. At power on, a brief positive pulse is applied to the base of Q2 via C2. Q2 will be on, and activate relay A/2.
The network of C3 and R4 form a low current holding circuit for the relay. Relay A/2 is a 12V relay with a 500 ohm coil. It requires slightly less current to keep a relay energized than it does to operate it. Once the relay has operated, the current through the coil is reduced by R4, saving power consumption. When Q2 is off, C3 will be discharged, but when Q2 becomes active (either at switch on or by pressing S1) capacitor C3 will charge very quickly via the relay coil. The initial charging current is sufficient to energize the relay and current flow through R4 sufficient to keep it energized.
Q1 bias is applied via R3 which is tied to Q2 collector. As Q2 is on, the collector voltage will be low, close to 0v and therefore Q1 and LED L1 will be off. As Q1 is off, its collector voltage will be high, and Q2 bias voltage is applied via the chain L1, R1 and R2. The curtains should already be fully open.
If now S2 is pressed, the base voltage of Q2 will become 0 and Q2 will switch off. In switching off, its collector voltage will rise to the supply voltage and Q1 will now be forward biased via the relay coil A/2, R4 and R3. LED L1 will now be lit, relay A/2 will be de-energized and as Q1 collector will be low, Q2 will be off and the circuit latched in this condition.
At the same time as S2 is pressed, the trigger input of IC1, a 555 timer (normally held high via R7 will be taken low. A timing sequence now commences. Duration is controlled by preset P1 and C6 and the timing is adjustable between about 1 and 12 seconds. This delay is adjusted so that the motor will run for sufficient time to fully open or close the curtains. The output of the 555 turns on Q3, fed via R8 which now applies power to the motor via relay contacts A1 and A2.
At any time the motor is in operation, and for any direction, LED L2 will always be lit. Contacts A1 and A2 reverse the polarity of the voltage appearing at the motor terminals,
Automatic Operation
The circuit can be broken down into three main parts; a bistable latch, a timer and a reversing circuit. Toggle switch S3 determines manual or automatic mode. The circuit as shown above is drawn in the automatic position and operation is as follows. The bistable is built around Q1 and Q2 and associated circuitry and controls relay A/2. S1 is used to open the curtains and S2 to close the curtains. At power on, a brief positive pulse is applied to the base of Q2 via C2. Q2 will be on, and activate relay A/2.
The network of C3 and R4 form a low current holding circuit for the relay. Relay A/2 is a 12V relay with a 500 ohm coil. It requires slightly less current to keep a relay energized than it does to operate it. Once the relay has operated, the current through the coil is reduced by R4, saving power consumption. When Q2 is off, C3 will be discharged, but when Q2 becomes active (either at switch on or by pressing S1) capacitor C3 will charge very quickly via the relay coil. The initial charging current is sufficient to energize the relay and current flow through R4 sufficient to keep it energized.
Q1 bias is applied via R3 which is tied to Q2 collector. As Q2 is on, the collector voltage will be low, close to 0v and therefore Q1 and LED L1 will be off. As Q1 is off, its collector voltage will be high, and Q2 bias voltage is applied via the chain L1, R1 and R2. The curtains should already be fully open.
If now S2 is pressed, the base voltage of Q2 will become 0 and Q2 will switch off. In switching off, its collector voltage will rise to the supply voltage and Q1 will now be forward biased via the relay coil A/2, R4 and R3. LED L1 will now be lit, relay A/2 will be de-energized and as Q1 collector will be low, Q2 will be off and the circuit latched in this condition.
At the same time as S2 is pressed, the trigger input of IC1, a 555 timer (normally held high via R7 will be taken low. A timing sequence now commences. Duration is controlled by preset P1 and C6 and the timing is adjustable between about 1 and 12 seconds. This delay is adjusted so that the motor will run for sufficient time to fully open or close the curtains. The output of the 555 turns on Q3, fed via R8 which now applies power to the motor via relay contacts A1 and A2.
At any time the motor is in operation, and for any direction, LED L2 will always be lit. Contacts A1 and A2 reverse the polarity of the voltage appearing at the motor terminals,
Great post.Thanks for sharing this article with us.keep posting!!!
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