Hello,
I am not very good with electronics, I want to control about 300 Relays with a stand-alone board or with a computer .
Can Arduino do this for me ?
Thanks
The first question is what are the relays being used to turn on? Because maybe a transistor could do the job for you instead? You are going to need transistors anyway to drive the relay. Check this pic for the type of configuration
Note the protection diode. The input will be the Arduino pin, you can try a 1K resistor.
The Arduino only has 14 digital outputs so you would need to do some multiplexing to get this to work.
There are many options you could use like shift registers or decoders or even something like Charlieplexing, which you can find lots of info on these.
For starters check out this application note from ST www.st.com/stonline/books/pdf/docs/13709.pdf
There are even IC's that can do this for you. Just be careful with relays and make sure that you put in the protection diode otherwise some of your silicon can go up in smoke. Also remember a relay suffers from contact bounce and can be noisy not just from a sound point of view but also electrically. 300 relays clicking away might make a bit of noise and be a bit expensive as well.
I found this in the Playground now as well: http://www.arduino.cc/playground/Main/InterfacingWithHardware#Multiplexing
zageek, Thanks for your replay ..
About realay quantity, I want to control 300 electromagnets. is there any better solution than relay ?
What you`ll do with so many relays? :o
On a project of this scale, you sholud seriously consider a modular aproach.
Design a "module" that can control a group of relays / electromegnets, test it and make sure it performs the way you want, then add more modules. If you chose to use shiftregisters as a way of expanding the digital outs on Arduino a suitable module size could be 8 electromagnets because most shiftregisters has 8 outputs.
One thing you should start considering from the start is your powersupply. powering 300 electromagnets is probably going to require a VERY large powersupply. You should probably also consider using more than one.
About realay quantity, I want to control 300 electromagnets.
Drive them directly as if they were motors.
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html