help need in triggering interrupt............

[sanddune008]

Hi All,

Need ideas in design triggering circuit....

basic idea:

triggering int when the switch is closed........were the switch is connected to 240V AC, 60Hz supply......All I need is a pulse at the int pin when switched ON.

Felt using transformer could increase the size of the board......Is there a way to reduce the size of the board using optocouplers or something else if so how?

Can relay be used for triggering?

Thanks to all in advance

 

[sanddune008]

Can thyristor be used to detect the closing of the AC switch.

 

[sanddune008]

can someone give me information?.........all i need is pulse to INT pin when AC switch is closed .........

 

[Pommie]

You just need a very large resistor (10MΩ) between the switch and the pic pin. You will get an interrupt every cycle and this is used by some circuits as a zero crossing detector. Have a read of this Microchip application Note.

Mike.

 

[sanddune008]

Thanks mike.....

will this provide the necessary isolation b/w high and low voltages........will it prove efficient at power surges........

 

[Pommie]

This will not provide isolation but will be safe if,
the neutral is earthed,
the phase is fed through the resistor,
it is constructed correctly,
the resistor is suitably large (physically) so that arcing is not possible (maybe use two).
If you don't understand any of the above points then it isn't safe for you to do.

Also,
The part before the resistor will not be safe.
It will not survive a lightening strike.

It would not be advisable to work on this without a suitable protection device (RCD).

Mike.

 

[sanddune008]

Mike......Thanks for your time.....

I need to Keep things safe......and i need isolation.

Could there be there be any other option say using triac or high voltage optocoupler?....that can send a pulse once the switch is close.....

Can I use combination of resistor as mentioned by mike and optocouplers ( to provide the necessary isolation)?If so how?

 

[sanddune008]

I found following optocouplers below is the link:

http://www.datasheetcatalog.org/datasheets/90/486754_DS.pdf
and
http://www.datasheetcatalog.org/datasheet/vishay/83676.pdf

Cant this be used?

 

[sanddune008]

I found an AC switch detector .....follow link

**broken link removed**

will this useful for achieving the above idea?

can someone answer?

 

[sanddune008]

I found an AC switch detector .....follow link

**broken link removed**

will this useful for achieving the above idea?

can someone answer?

 

[Pommie]

You could use the opto isolator you linked to but you would need a 50K resistor in series with the LED. This resistor would dissipate ~1.5W and so would need to be suitably rated.

Maybe if you described what you are trying to do, members would be able to advise on the best method.

Mike.

 

[sanddune008]

Maybe if you described what you are trying to do, members would be able to advise on the best method.

Mike.

Detecting a door bell....

A closed switch(door bell switch) will trigger my micro controller to send certain commands.

You could use the opto isolator you linked to but you would need a 50K resistor in series with the LED. This resistor would dissipate ~1.5W and so would need to be suitably rated.

Mike.

Is this correct:
I would be connecting my INT pin of my micro controller to the 3rd PIN of SFH620AA(siemens), With the Pin 1 connected through 50 K resisto to the supply

how do i select a resistor with the above ratings?....any way to calculate the same resistor value?

Thanks for all the assistance

 

[Pommie]

I have never seen a door bell that works on 250V! (except via a transformer) I think you will find that a much lower voltage goes to the bell push. Imagine, in a storm, someone pressing a soaking wet bell push connected to 250V - they would be electrocuted.

To accomplish what you desire could be as simple as rectifying the voltage to the ringer/bell/sounder and powering the circuit from it. Whether you can do that depends on what commands you need to send.

Again, a better description of what you are trying to accomplish would help.

Mike.

 

[sanddune008]

thanks mike..............

I have never seen a door bell that works on 250V! (except via a transformer) I think you will find that a much lower voltage goes to the bell push. Imagine, in a storm, someone pressing a soaking wet bell push connected to 250V - they would be electrocuted.
Mike.

yes exactly door bell is connected via transformer............

what I need to do is as soon as when someone outside uses the door bell switch (using this criteria to determine whether bell is active or not) need to ask micro controllers to send control commands eg an visual indication for deaf people. .

To accomplish what you desire could be as simple as rectifying the voltage to the ringer/bell/sounder and powering the circuit from it. Whether you can do that depends on what commands you need to send.

Yeah i know this..... As i mentioned earlier, using rectifier is certainly an option. i would be looking at reducing my board size without an transformer and rectifier circuit, After all i need is an indication of whether the door alarm is activated.

 

[sanddune008]

I guess i will go with

Connecting my EXT INT pin of micro controller to the 4th PIN(C) of SFH620A(Vishay), With the Pin 1 connected through 50 K resistor supply(240V). With the optocoupler connected in series with the switch.

Is there anythings I need to take care?besides the current limiting resistor at the AC input stage?.