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I would like to implement a home-automation system on my arduino. For this project I would like to communicate with the different devices by radio frequency. So that would be different 433 mhz receivers and one 433 mhz transmitters.

Now my questions:

  1. How can the transmitter differentiate the signals of the indiviual devices. Do they each have an unique id or such? Or do i need some other part or controller to identify them?

  2. What is the purpose of a transmitter encoder?

I'm rather new with electronics and arduino so any comment or suggestion is appreciated.

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  • \$\begingroup\$ Are you sure you don't mean 434 MHz? \$\endgroup\$ – Olin Lathrop Jan 2 '12 at 13:50
  • \$\begingroup\$ @Olin Lathrop Actually 433 MHz modules are common too an can be often found in various devices. \$\endgroup\$ – AndrejaKo Jan 2 '12 at 17:41
  • \$\begingroup\$ @AndrejaKo: Actually I was referring to the OP originally saying 443 MHz or something like that. I see he has meanwhile fixed that, sortof. I'm guessing he really means the ISM band at 433.92 MHz, which I rounded to 434 MHz. Since he is now specifically saying 433 MHz, I'm not sure what he means. Can you show some modules that do 433 MHz? \$\endgroup\$ – Olin Lathrop Jan 2 '12 at 18:13
  • \$\begingroup\$ @Olin Lathrop Well, this one is advertized as 433 MHz. This one is also in 433 MHz band. There's also an article on Wikipedia. \$\endgroup\$ – AndrejaKo Jan 2 '12 at 18:36
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    \$\begingroup\$ @Andrej: If you follow the first one all the way to detailed specs (page 10 of the datasheet which you have to find separately), you'll see it's really 433.92 MHz as I said. Apparently they didn't learn to round very well. I didn't follow the others, but I suspect most if not all "433 MHz" modules are really misnamed and operate at 433.92 MHz since that's one of the unlicensed ISM frequencies. \$\endgroup\$ – Olin Lathrop Jan 2 '12 at 19:16
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As you describe it, with one way communication from a single master to many "slaves", the task is very easy.

The master simply sends messages of the form Address + Data. All slaves hear all messages and each slave checks for message with its own address and actions them while ignoring the rest. As the master has complete control of the transmitting this can make very efficient use of the channel capacity (when efficiency is needed).

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If you want to go the other way and have many "outposts" sending messages to a single central location in response to messages from the Master (usually on a channel of its own) "the fun begins". Out of such a need has risen much of the data comms protocols that we see today, and the internet.

The (or a) classic early initiator was named "Aloha Net" ("Hello Net") operated by the University of Hawaii to outposts around the islands. This used the simple method of an outpost "just sending a message when it had one". If it did not get an acknowledgement within a certain randomly set time it would send it again. This allowed for radio fade and noise and collisions with other messages. This works well when the total message transmit time is a small percentage of the tome available and when message lengths are short compared to time between messages. This would often apply to home automation applications, allowing an easy two way communications protocol when you find you need or want two way commiunications - as you soon will :-).

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