Extending the range of 1-Wire network (DS2482)

Details

Connecting the 1-wire sensors directly to the RPi does allow to test various concepts... I does not, however, suffices the needs of home automation.  There are two reasons:

• Connecting the sensors directly to the RPi pins is risky - it can lead to damaging the RPi itself,
• The pins do not provide sufficient current to power and extensive network with many sensors.

To check if a RPi-based system can at all fit my automation needs, I have built 2 testing modules based on Maxim's DS2382-100 and DS2382-800.

All that you see here is an effect of mixing and digesting examples found on the net.  I have repeatedly concluded that I have not clue about what I am doing.  At the end, however, I have managed to design and make a PCB, solder the elements and run the modules.  Nevertheless - beware! ...and if you find errors, please let me know.

The first step was making a PCB project.  On the www.temperatur.nu forum I have found an scheme of  an example RPi extension. One can also buy a ready board at www.m.nu. Looking through the pictures and analyzing the list of the elements I managed to 'decode' what fits into what.  Don't laugh.  This is the first time I ever noticed that there is a difference between a capacitor and a resistor.  Designs found at www.abelectronics.co.uk. helped a lot.  Finally my schemes look as follows:

In case of the board using DS2482-100 I have decided to provide pins (here – SV1), which allow changing the I2C address. Such a possibility should - if needed - use more than one module at the same time.

I have spent a lot of time thinking, how all the wires should be connected.  Should the modules be powered through a microUSB plug, should I use RJ.. plug for I2C.  At the end I chose screw terminals.  They fit well to all the rest of connections around.

Here are the images of my boards:

The photos of boards shown at the beginning differ slightly from the images above.  I have found and corrected some errors.  As an example - the P6E6.8A has been replaced by SMBJ6.0A, which was unavailable to me at the time of first soldering.

The boards in the DIN cases look as follows:

All who - similar to me - have had fear for soldering should know that making a PCB is extremely easy and very rewarding.  The boards you see above are the first in my life.  A thin soldering wire, borrowed iron, half an hour spend watching the EEVBlog... and that's it.  The whole thing is not hard at all... and the joy of entering a mysterious terrain of electronics is priceless (even if one does not understand everything...).

The modules you see above are powered from an external 5VDC source.  The 1-wire communication and GND are protected with DS9503P.  The 5VDC wire powering the 1-wire network is protected with a polyfuse (1206L050YR) and a transil diode (SMBJ6.0A).

In order to test the capacity of the modules I still need to build the network - i.e. place the sensors around my house.

Now a bit of theory and programming. DS2482 are bridges between I2C and 1-wire networks.  On the side of the RPi the pins 1 (3.3VDC), 3, 5 (SDA and SCL of I2C) and 6 (GND) are used.  It is also necessary to install software related to I2C itself and changing the scripts.  The Rpi should no longer control the 1-wire communication by itself (through GPIO4) but should use the I2C instead.  The needed commands are:

nano /etc/modprobe.d/raspi-blacklist.conf

and adding „#” before „blacklist i2c-bcm2708”, then:

nano /etc/modules

and adding at the bottom  „i2c-dev”. In the next step install the tools related to I2C:

apt-get install i2c-tools

After you restart your RPI and enter:

i2cdetect -y 1

you should see a table showing the found devices which use I2C.

For OWFS to read sensors connected to DS2482 you need:

• Install OWFS by entering: apt-get install owfs ow-shell,
• Create a directory by entering mkdir /mnt/1wire,
• Check if in  /etc/fuse.conf the line "user_allow_other” is free from „#” in front,
• Run OWFS by:

/opt/owfs/bin/owfs --i2c=ALL:ALL --allow_other /mnt/1wire/

(owfs might install into other directory like: /usr/bin/owfs)

The found DS2482 bridges and sensors can be found in the /mnt/1-wire directory.

You will be better off reading and following a great tutorial presented at http://wiki.temperatur.nu.

On the PHP side It was necessary to modify the scripts:

<?php
if ($MainDir = opendir('/mnt/1wire/bus.0')) {
	while (false !==($MainDirItem = readdir($MainDir))){
		if (preg_match('/[0-9]{2}./', $MainDirItem)) {
			$TempFile = fopen("/mnt/1wire/$MainDirItem/temperature", "r");
			if (!$TempFile) {
				echo "...some problems with temp. file opening...";
			}
			else {
				$Temperature = fgets($TempFile);
				echo "Temperature of ".$MainDirItem." = ";
				echo $Temperature."°C";
			}
		}
	}
}

So much for now.  If you are interested in making a PCB, please take a look at Appendix 1 - making a PCB.

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