Hello I found these project online its called vent a garage. It has 2 ac fans the LINK DEPOT 120mm AC Cooling Fan (AC-FAN-1238B) and its controlled by a thermostate. What I have plan is to use the arduino and a temperature sensor to turn on the fans when for example reaches 70 degrees. what I dont know is what to use to link the 2 ac fans to the arduino to communicate.
I hate it when tutorials provide advise that is less than SAFE.
The above is WRONG.
1. It needs to be fastened and NOT floating around.
2. The wires should not be soldered before entry into a compression style connection, as if there is any heating the solder retract and the connection become poor.
it either makes it worse or potentially hazardous.
3. they don't show any form of cable clamp to stop it getting pulled out the box.
4. The board design leaves a lot to be desired.
They are relying on a clearance across the pcb of slightly under 2mm ... it should have a physical cut between the track carrying mains voltage and the relay coil.
(they have put the low voltage side on the other side of the pcb which is wise)
I agree with the other replies.
If you are unfamiliar with this then remain unfamiliar and buy something like this which can be controlled remotely from an Arduino.
Mark
Peter
As I said in the PM, having the link in place helps others if they follow it, and given the warning I provided could be made safe.
In many cases the person is ignorant because they don't know, so understanding the reasons and things to look for is part of learning.
I'm less worried about people playing with mains voltages and killing themselves, than I am for them to leave a death trap for someone else.
Most electrocutions aren't because someone intentionally touched the mains, its the un-intentional contact that causes problems. 
Besides the electricity being able to kill you, the force of the shock can cause physical injuries as you are thrown across the room, or off the ladder, etc.
RCD's do provide some help in removing the power (after you've gotten the shock), but not all circuits are required to have them, so treating all mains as deadly is far better.
Bernardo
Is there a reason why you can't just add a manual thermostat set at 70 deg to turn the fans ON.
I applaud you wanting to learn, but I suggest using the arduino to measure the temperature and maybe warn you.
You could follow this article we did to give you a high and low setting (sorry we used celcius)
http://www.theshedmag.co.nz/online/images/stories/downloads/arduino/arduino-101-part4.pdf
The sketches are just to the right, and the LCD isn't required if you don't want it.
Mark
Agree with most points.
For strain relief, there is built in strain relief on the box, if you look carefully you will see it In the picture
Top left corner, it is north American box and outlet. NOW the strain relief is not meant for a box left floating un attached. It is for when it is mounted on a stud and with drywall etc around it so in this case it will not be adequate, this is a common misunderstanding over here
should be something more like this
or something from this set of images appropriate to your region https://www.google.ca/search?q=power+cable+strain+relief&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ei=LdPnU-uNLIyYyASGsoHwA…
The socket is good for USA and Canada, not UK or Europe or pretty much any other country (You know what your sockets look like.
Also, if your going to do this, don't do this board, it is not worth it and as MCB pointed out, it has issues
This one from Spark fun is not expensive, seems to be designed much better and has appropriate cable connectors suitable for the job
Oh and going solid state all the way with something like this https://www.sparkfun.com/products/11042
https://www.sparkfun.com/products/13015
This unit requires nothing else, you can control it directly from an Arduino or any other micro-controller, as it only needs 3V to energise and will take up to 32V. It can easily screw into any box it fits into
Regards
peter
Peter
I agree that is a much better solution ...well done.
I have heard that there are some solid state relays using "... less than optimal parts ...." inside, so its is wise to run them at full load then remove the power and check if they get hot.
The markings make them look like a genuine thing, but they are apparently a poor copy.
The true test of any of these is the 1000v DC ( megger ) check between any of the Mains side and the low voltage control side and the metal mounting plate.
For those interested element14 has these ( on special for NZ$122 ).
Mark
