passing 12 v throught pc817

[dallli92]

sorry but it didint work either :/

[CNCMAN172]

dalli92,
When you hook up 12VDC to the relay do you hear a little click? If it is not clicking make sure you hooked up the + and - to the relay correctly from your supply. If it is clicking take a ohm meter and make sure the contacts are changing from open to closed. If that works the relay will be able to control the fan with no issue. Need to add a transistor if you want the andrino to control it like KHOUJ showed.
Russ

[KH0UJ]

sorry but it didint work either :/

Can you post a picture on the actual sir? what's the number of the transistor? Sometimes locating the BCE can be confusing

[CNCMAN172]

As KHOUJ said the pins on the transistor change depending on the model. A typical general purpose NPN transistor 2N3904 for example is assigned EBC looking at the flat side from left to right.

Russ

[dallli92]

you know i am confuses , once someone tell me to use a relay with a transistor, then they told me to just use a transistor. all i need is i have a linkit one card working like arduino attached to a temperature sensor when it reach a value i want to start the fan i have all needed pieces. please help . clear schema if possible and thank you.

[CNCMAN172]

dalli92,
Step#1 verify if the 12V relay actually works, connect it to 12V supply directly and make sure it clicks on and off and you add and remove the power. Once you can hear it clicking double check the contacts to make sure they are opening and closing.
Step#2 We know your are confused, but you can use that relay to turn on the fan, but now we need to determine how to activate the relay, due to limited current output from an Ardrino port we need to add a transistor which can carry enough current to activate the relay.
Step#3 Whiles some people might have said you can use a transistor by itself, this is also correct if you select the right transistor. A transistor can act just like a switch if you have the right transistor that can carry enough current. Let's skip this option right now since you have a relay.
Step#4 We need to see the exact part number of your transistor, to determine if it will work. If you have already tried to connect the transistor you might have destroyed it so make sure when we set this up again you are using a new unused transistor.

Once you have done these steps we can move forward. Does this work for you?

Russ

[dallli92]

the relay works fine, when I conect it to 12v it make that "tik" sound and it has 4 pins , and I have 3 2n3904 transistors and I have 12v from lm7812 for the fan and lm7805 for the card as I sayed I have all the pieces that I need, but I dindt connect them correctly , plelase tell me if I need the relay or not in both cases please how my schema would be. thank you

[CNCMAN172]

Here is the circuit for you. Keep in mind this will only support a fan that consumes less than 1.5A. The 7812 typically outputs 12V at 1.5A. The 7812 feeds the 7805 which outputs 5V to wherever you need that voltage. The transistor needs a resistor about 330 to 1000 ohms on the base, and when the Ardrino outputs a high it will click on the 12V relay will will provide the ground side to the fan and it will spin.

Russ

[dallli92]

waht about the relay , I connect only two pins the + - pins only ?

[CNCMAN172]

dalli92,
Look at the picture closely. There are four pins on the relay, two for the coil and two for the contacts based on the photo you posed. They are right next to each other in the drawing, the thing that looks like a switch contact is actual the relay contacts.

Russ

[dallli92]

aah ok i got it , I will give it a try and tell you , Iam so gratefull for your help and your time,
if I face an issue I will tell you please dont get bored from me,
thank you a lot