Raspberry Pi I2C

I have a Raspberry Pi and lets face it, who doesn't?

I have played with linux on many architectures before including PPC, Hitachi, MIPS, PA-RISC and Sparc so I figure I had better have a go at ARM too.

Apart from playing around, I plan to create a light controller module for my garden lights. This will require some hardware hacking which is always a bit of fun but my main plan is to bring it together with some fancy software.

In previous projects I have interfaced with GPIO and I2C to run door controllers and read swipe cards (Mostly on the WRT54G).

I could not find accurate instructions for getting I2C going on the rpi so here are my instructions for users for raspbian:

Install some tools

# apt-get install i2c-tools

edit  /etc/modprobe.d/raspi-blacklist.conf and comment out the line


i2c-bcm2708

I don't know why it comes as blacklisted.

edit /etc/modules and add the lines

i2c-bcm2708
i2c-dev

This will make sure the drivers are loaded during the boot.

create a file /etc/udev/rules.d/99-i2c.rules and add the line

SUBSYSTEM=="i2c-dev", MODE="0666"

This will give all users access to the i2c devices. You could instead set the owner or group but the rpi is not normally being used as a multi-user device

Now you can test these changes without a reboot:

modprobe i2c-bcm2708

modprobe i2c-dev

udevadm trigger
ls -l /dev/i2c*

And you should see output like this (Your date will be different):

crw-rw-rwT 1 root i2c 89, 0 Nov 18 22:36 /dev/i2c-0
crw-rw-rwT 1 root i2c 89, 1 Nov 18 22:36 /dev/i2c-1

If that works, reboot and run the ls again. The devices should be there and have world read/write permissions.

Now, to connect up some hardware and show that it works. Look for a new blog soon.

Samba guest access

I was trying to share some photos for my wife to download from my linux desktop machine (CentOS 6). I had ~10Gig of photos but she only wanted a hand full. I though the best option would be to share out the folder using samba and she can use windows explorer to pick the ones she wants

Well it seems simple now but it took a few tries to get it working.

I use security=server which is not the most secure method but it is normally easy & convenient. It also seems to be poorly documented, particularly for more recent samba releases and versions of Windows.

My wife has an account on the password server but not on my new desktop. Guest access I though would be a simple solution here but no so. The problem is that guest access will not work by default when using security=server (despite what the man page says). There is a new setting called map to guest which defaults to Never. I had to change this to Bad User to get it to work.

There are the relevant parts from my working smb.conf:

security = server
password server = myserver

map to guest = Bad User

[photos]
comment = John's photos
path = /home/jnewbigin/photos
guest ok = yes
writable = no
force user = jnewbigin

So now it is working and I am happy and my wife is happy too.