hi.. I am making a simple automatic sliding door with an LDR sensor and a triac to drive the motor.
the problem is when the door is open i dont have an idea to close it. what will i do to reverse the polarity of the motor?

 

You need H bridge.

 

Hello,

What kind of motor do you use?
Also keep in mind that you block the movement of the door when there is something in the doorway.

Bertus

 

You need H bridge.

What is an h bridge sir

 

Hello,

What kind of motor do you use?
Also keep in mind that you block the movement of the door when there is something in the doorway.

Bertus

I am using a servo motor

 

How are you driving the servo motor to open the door? Servos operate differently than DC motors.

 

What is an h bridge sir

H-Bridge is a circuit which can drive the motors in forward and reverse.

http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/

 

H-Bridge is a circuit which can drive the motors in forward and reverse.

But not a servo.

 

How are you driving the servo motor to open the door? Servos operate differently than DC motors.

I have also here a dc motor sir. Which on I will use

 

But not a servo.

Didn't see he was using a servo. Servo is driven with PWM, NE555 can be used.

 

Thank you for the help sir. I will do a research about this h bridge and how to use it.

 

You can also drive a servo motor with plain DC which is reversed by contactor or relay.
PWM is if you require rpm control.
This is assuming it is not a simple RC servo but an industrial one?
Max.

 

What is the size of your motor?
'H' bridge, you could use a L298
http://www.tech.dmu.ac.uk/~mgongora/Resources/L298N.pdf
If it's not powerful enough, you can boost it's output by using mosfets.

 

the problem is when the door is open i dont have an idea to close it. what will i do to reverse the polarity of the motor?

It sounds like you are powering it already to open it, you just need reversal?
It is wise to qualify in your OP whether it is a model RC servo type or other.
Max.

 

Can I combine this scr circuit with the h bridge sir ? instead of using the lamp in the scr I will change it with the h bridge together with the motor

 

Is it possible to combine the two circuit sir and how?