RS485 topology, end resistors and baudrate for home automation.

Rs485 can be used effectively over long distances and in electrically noisy environments, using linear bus topology with two end resistors.

RS485 linear bus topology

However Mixed topology is easier to implement in a house (that is my case)

RS485 Mixed topology without end resistors

In this case we can't put a resistor in every end of the cable.
In order to prevent data corruption, propagation delay should be much smaller (15 times or more) than one bit width, then end resistor is no needed.

In other words, maximum  baudrate depends on cable length.
As a rule, for cable length up 200 metres safe speed is 28600 bps and for cable length up 600 metres safe speed is  9600 bps.

In My Automatic House (MAH), in spite of cable distance is less than 200 mts I'm using 9600 bps which is enough for regular use.


References
The RS-485 Design Guide (Rev. B - Texas Instruments)
RS485 & RS422 - When is termination required?
http://en.wikipedia.org/wiki/RS-485

MININO board (1)

Minino is my arduino compatible board for home automation.

Features:

-Small size (able to fit inside an electrical box)

-Switching power supply (able to provide power supply to peripherals)

-Driver RS485

-Digital inputs protection for overvoltage, ESD,EMI

-Screw terminals (2,54 pitch) for wiring easily

-Plug for re-programming
-Not too difficult to build

-Very Low cost

-It's name finish in INO* for fully Arduino compatibility   ;)

MININO (model: Black L) top side

MININO (model: Black L) bottom side

*MININO means little cat in spanish

Starting.... More Than Blinking Leds

This space is for share projects and ideas about electronics.

Now I'm involved in the automation of my house (really my second house, placed in the little village where I born), so mainly I will talk about it.
For now there are 7 boards working running SOULISS and interconnected by rs485 managing lights, temperature and heating. I can access locally and remotely through OpenHab.
I had to make small boards and relays to fit in the electrical boxes

(Schematic ilustration of a Minino Board)

(Minino inside an electrical box)

Juan