arduinoreceiverRFtransmitter
I am working home automation using Arduino and TX/RX module.
From various sources I learned that Rolling Code based RF Switches are having better security.
I have following queries
How suitable it is to use FIXED code RF relays for Home automation. I need it for switching on and off lights and not for key locks.
Is it possible to generate rolling code using arduino for a given receiver working on rolling code RF.
Please help.
There are plenty of 5V relays available. The trick is getting ones that switch a high enough current.
If you can't find one, then use a 12V one and power it with 12V.
Whether you're using a 5V or a 12V relay you'll require something between the Netduino and the relay to be able to provide enough current to switch the relay - be that a transistor, or a chip like the ULN2803. Either of these can switch 12V as easily as 5V.
If you want to use the ULN2803 with the Arduino/Netduino I have designed a handy shield you can etch yourself with Toner Transfer.
The other option (which will be much quieter, albeit at more cost) would be to use a "Solid State Relay". This is essentially an opto-coupled triac which does the same job as a relay but without any moving parts (except photons). These, being opto-coupled, use about the same current to switch as an LED uses to light up, so can be linked direct to the Arduino/Netduino with nothing more than the normal current limiting resistor for an LED.
Added RM:
Majenko's 'shield' implements this circuit. Its a good useful universal driver circuit. Note the connection of pin 9 to V+. This connects the on chip catch diodes to supply to dissipate stored energy in the relay coils when they are turned off. If you don't make this connection you will end up with an exciting high voltage generator - possibly a short lived one.
(Circuit from(here) which does not give any other detail.
Mains power switches work exactly the same way as the relay, in terms of abruptly applying, or removing, power to the load. This is true whether the load is a lightbulb, or a television.
Thus, there is conceptually no difference between a relay and a wall switch in this context.
In practice, there is, however one caveat: Good quality light switches have internal spring action which ensures positive, firm contact making or breaking - a mechanical hysteresis of the manual force applied versus the switching on and off, so to speak.
A basic relay, or one that is energized by too low a current on the actuation coil, will suffer contact bounce, it will make and break the circuit repeatedly for a very brief period, or if the relay coil is just barely insufficiently powered, the relay contacts might chatter.
Standard relays designed for appliance switching on mains lines, such as those made by Omron and other appliance electrical manufacturers, address this issue by implementing a contact make/break hysteresis and firm spring action, thus achieving the positive force and stable contact creation that good wall switches do.
TL;DR: Don't use a cheap sugar cube relay or one not designed for household appliance switching. A good relay will cause just as much, or as little, harm to an attached appliance, as a wall switch does.
Best Answer
Using fixed code RF is suitable for your application, as long as you keep it just to lighting/opening curtains/other mundane things. The worst thing that could happen is that an obnoxious (and clever) neighbor figures out how to shut your lights off on you!
I would need to know which radio transceiver you are using and what the architecture of your system is to answer this question. I am 90% sure that the answer is "yes, you can make your own rolling code system"
As long as you can program all the nodes in your system yourself, you can make a rolling code system. Here is a bad example with very poor security, but maybe it will help you get the idea.
You have 2 arduinos that need to send ascii messages back and forth. you specify the following protocol: Each message is exactly 4 bytes long. The first 9 bytes contain the data you want to transmit. The last 1 byte contains a key that will be used to encrypt the next transmission. A basic encryption algorithm which adds a constant value to each letter can be used.
Here is an example: Before arduino 1 transmits its message, it encrypts it with our basic encryption algorithm. at startup, the encryption key for both arduinos is 0, so the letters in the first message aren't shifted.
Again, this is a HYPOTHETICAL example with very very poor security! I don't know your system architecture or the radio transcievers you are using, so I am not 100% sure if my silly little example would work for you. Even though this is terrible encryption, it would still deter any novice hackers. A real rolling code system is more complex than this. I'm just demonstrating that, as long as you can program all the nodes in your radio network, you can implement your own arbitrary rolling code system.