DS1621 with Raspberry Pi/ArchLinuxARM

Here is  how to get DS1621 I²C Temperature sensor working with Raspberry Pi running ArchLinuxARM

Make sure you have a working setup of RPi and Arch Linux, if not refer here:
HelloWorld in Lua on Raspberry Pi running Mihini on ArchLinux with Koneki as IDE

After you have the setup ready, attach the DS1621 sensor to your RPi as shown in the schematic below.
I have Model B Revision 1.0 Raspberry Pi (cat /proc/cpuinfo shows Revision : 0002)

DS1621 connected to Raspberry Pi (.fzz file here)

The following commands issues to RPi over a terminal (SSH or Serial using PuTTY):

1. Install i2c-tools:
   pacman -Sy i2c-tools
2. Install lm-sensors:
   pacman -Sy lm_sensors
3. Open kernel module load config file for editing:
   nano /etc/modules-load.d/raspberrypi.conf
4. Add the following line at the end of the file and save it.
   i2c-dev
   
   This will load the i2c-dev kernel module at boot up.
   This module will allow you to access the I²C bus via /dev/i2c-0
5. Reboot Raspberry Pi
6. When the Raspberry Pi comes back on, issue the following command:
   i2cdetect -y 0
   
   You will see the following output:

[root@alarmpi ~]# i2cdetect -y 0 0 1 2 3 4 5 6 7 8 9 a b c d e f 00: -- -- -- -- -- -- -- -- -- -- -- -- -- 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- -- 50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 70: -- -- -- -- -- -- -- --

Observe that DS1621's address shows up - it means it was detected successfully.


7. Now we need to tell Linux to instantiate the device, issue the command:
   echo ds1621 0x48 >/sys/class/i2c-adapter/i2c-0/new_device
   
   If you check the kernel messages using the dmesg command, you will see the following new entry:
   i2c-0: new_device: Instantiated device ds1621 at 0x48
8. To read the temperature issue the command:
   sensors
   
   and you will get an output similar to:
   
   

   [root@alarmpi ~]# sensors
   ds1621-i2c-0-48
   Adapter: bcm2708_i2c.0
   temp1:        +23.5 C  (low  = +10.0 C, high = +15.0 C)  ALARM (HIGH) 

Using Lua:
And in case you have Eclipse M2M tools installed on your PC and RPi, here is a lua script which will instantiate a DS1621 and display the temperature once every second:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

-- Instantiate a DS1621 device on I2C bus 0 -- And display its reading once every second package.path = '/opt/mihini/lua/?.lua;/opt/mihini/lua/?/init.lua;' .. package.path package.cpath = '/opt/mihini/lua/?.so;' .. package.cpath local sched = require "sched" local os = require "os" local socket = require "socket" --------------------------------------------------------------- local function main() -- Idle task while true do local temp_file=io.open("/sys/devices/platform/bcm2708_i2c.0/i2c-0/0-0048/temp1_input","r") if temp_file~=nil then local temperature = temp_file:read() temperature = tonumber(temperature) temperature = temperature/1000 print(string.format("Time %15s | Temperature = %f",os.date("%X"), temperature)) temp_file:close() end sched.wait(1) end end --------------------------------------------------------------- -- -- Schedule the idle thread local configfile = io.open("/sys/class/i2c-adapter/i2c-0/new_device","a") if not configfile then return nil end configfile:write("ds1621 0x48") configfile:close() sched.run(main) -- -- Start Scheduler sched.loop()

Output will look like:

Time        16:22:21 | Temperature = 28.500000
Time        16:22:22 | Temperature = 28.500000
Time        16:22:23 | Temperature = 28.500000
Time        16:22:24 | Temperature = 28.500000

NOTES:

1. To check the current speed of the IC bus in hertz, you can issue the command:
   cat /sys/module/i2c_bcm2708/parameters/baudrate
2. Change the bus speed to, for example 500 Hz, issue the following three commands in succession:
   echo bcm2708_i2c.0 > /sys/bus/platform/drivers/bcm2708_i2c/unbind
   echo 500 > /sys/module/i2c_bcm2708/parameters/baudrate
   echo bcm2708_i2c.0 > /sys/bus/platform/drivers/bcm2708_i2c/bind

References:

1. Adding an I2C Temperature Sensor Using an Existing Linux Driver
2. Raspberry Pi Rs-Pi internal USB HUB & Multi-function I2C RTC Board