Controlling Electrical Appliances using PC

[engg_rsakm]

Hi There

I Am Currently Building A Project That Controls Different Electrical Appliances I Have Completed My Circuit And Software For That Kind Of Interfacing But I Still Am Having Some Problem With My Circuit It Does Not Work Properly I Does Not Turn The Divice On And Of As It Should Do U Can Check The Circuti Diagram And Plz Guide Me Soon Waiting For Replies

Thanks

 

[dknguyen]

I don't see anything obviously wrong with your circuit...has it ever worked? I am curious why you didnt' just connect it the transistors directly like this though:
Filearlington configuration.svg - Wikipedia, the free encyclopedia

It might better to use a 1N4448 or a schotky transistor since they are faster than your 1N4001 and would protect the NPN better. Also, wHy are you using an optoisolators? Mechanical relays by definition have a very high degree of isolation and would more than protect your PC from the AC mains. I am thinking you could drive the NPN transistor directly with your parallel port.

If you remove the optoisolator and place a wire in it's place across 4-5, does it work? Maybe it's the opto. I am looking at the opto datasheet and it seems like your drive current may be too low.

 

[Mike_2545]

This may be simplified,but have you checked the pin out of the transistor? EBC gets turned around when looking from the top to bottom.

 

[engg_rsakm]

My switching is not going well with the relay could there be some problem with because my relay specification is 120VAC and giving it 240 VAC from the house outlet can this effect my switching

And please confirm me that if i remove the optocoupler woould it be dangerous for my parrallel

 

[didimus]

the dude "dknguyen" is right. You do not need the opto coupler. Relays are generaly used in isolation purpouses. I would check two things: first, have you checked if your parallel port programing is right? ( are you getting 5V out in the desired pin?). Second reduce the resistor value in series with your port. maybe 100 Ohms e check if the opto coupler is on.

 

[ericgibbs]

My switching is not going well with the relay could there be some problem with because my relay specification is 120VAC and giving it 240 VAC from the house outlet can this effect my switching

And please confirm me that if i remove the optocoupler woould it be dangerous for my parrallel

hi,
The opto coupler is essential for safety.

Have you wired the circuit exactly as shown in your diagram.?

Which PC operating system are you using, eg: Windows 98, XP Pro etc.

To test the circuit it is not necessary to have mains connected to the relay contacts.
When the relay operates you will hear it 'clicking'.

As a simple test, remove the 470R connected to pin 4 of the opto to the transistor.
touch the free end of the 470R to +6V, the relay should operate.

If that worked OK, reconnect the 470R, then remove the 470R from pin 2 [D0] of the 25way connector,
connect the free end of the 470R to +6V, the relay should operate.




Do you follow OK.?

 

[didimus]

hi,
The opto coupler is essential for safety.

Have you wired the circuit exactly as shown in your diagram.?

Which PC operating system are you using, eg: Windows 98, XP Pro etc.

To test the circuit it is not necessary to have mains connected to the relay contacts.
When the relay operates you will hear it 'clicking'.

As a simple test, remove the 470R connected to pin 4 of the opto to the transistor.
touch the free end of the 470R to +6V, the relay should operate.

If that worked OK, reconnect the 470R, then remove the 470R from pin 2 [D0] of the 25way connector,
connect the free end of the 470R to +6V, the relay should operate.




Do you follow OK.?

I disagree. At your configutarion, If you have your parrallel port linked to the base of you bjt, your AC mains will never damage you computer.

 

[ericgibbs]

I disagree. At your configutarion, If you have your parrallel port linked to the base of you bjt, your AC mains will never damage you computer.

The OP has very limited knowledge, if he incorrectly wires the relay/mains he will have NO protection.

IMHO for someone experimenting with PC controlled mains devices, the cost of an opto isolator is a small price to pay for extra isolation protection.

The other VERY important point he using relay specified for 120Vac on a 240Vac circuit, if the relay isolation fails he could have mains connected back onto his logic board and PC.

How would you feel if he followed your advice and that happened.

 

[dknguyen]

Is he using a 120V relay for 240V? Oy. I'd just get another relay- and use a 9V or 12V battery as the "AC Mains" during testing with a resistor or something else tiny and low voltage during testing to make sure it all works before you connect it to the AC mains.

 

[ericgibbs]

Is he using a 120V relay for 240V? Oy. I'd just get another relay- and use a 9V or 12V battery as the "AC Mains" during testing with a resistor or something else tiny and low voltage during testing to make sure it all works before you connect it to the AC mains.

my relay specification is 120VAC and giving it 240 VAC from the house outlet can this effect my switching

Hi,
This what he has said, I agree he should test the relay switching using a low voltage and get the correct rated relay.

 

[didimus]

Okay, since the OP does not have that much knowledge, the opto coupler may be a good idea ( hoping he does not mess the wires with that either!!!).

For the relay, the problem with using a under estimated relays by be heating. It may heat a lot and damage your relay.

Third agree, test it without the power connected and use a multimeter for continuityor lower power. Listen for the relay "clicking".

 

[Mike_2545]

Giving 240 volts to a 120 volt coil will kill the relay! If you have limited experience dealing with these voltages stay safe, use the component with the correct rating, and always, yes always use an opto isolator when low voltage such as TTL is interfacing with AC power. Relays are electro-mechanical, and if you can show me a mechanical system that does not fail sooner or later I've got some great beach front property in Colorado to sell you! I even use opto isolators when mixing low voltage systems like 12v, these can kill a micro controller just as quick.

So lets review: opto isolator-Good
240 volts on a 120 volt relay-Bad

 

[mneary]

Giving 240 volts to a 120 volt coil will kill the relay!
.
.
.
So lets review: opto isolator-Good
240 volts on a 120 volt relay-Bad

The diagram shows that it is a 6 volt 100 ohm coil. The OP wants to know whether he can abuse the 120V contacts with 240V, the answer is still NO, but it's a good idea to answer the question that was asked.

 

[Mike_2545]

Abuse Contacts?
I guess we should both slow down and read what is in front of us.
touche

 

[Boncuk]

I disagree. At your configutarion, If you have your parrallel port linked to the base of you bjt, your AC mains will never damage you computer.

I go along with Eric!

I guess a computer doesn't care much if the UART is blown by mains or backfiring 12V - which might happen in extreme cases.

It is not wise to connect anything to the parallel port without any protection circuit. May it be an opto-coupler or just a buffer.

Better spend a few Cents for some kind of protection instead of learning the hard way - purchasing a new main board.

And last not least increase sales for Intel.

Boncuk