Automatic Temperature Measurements Using NSLU2

The NSLU2 is a small computer, that was sold as a NAS device by Linksys. NAS stands for Network-Attached Storage which means that you can connect a hard disk to your network, hence the name Network Storage Link for USB 2.0 Disk Drives.

It was discontinued in 2008, but I still have three old units that I have used for different purposes in the past. One of them was used in a 1-Wire thermometer system like this:

The good thing about the NSLU2 is the low power consumption, around 5 watts, which means that you can leave the unit on 24/7 without it showing up on your electrical bill.

The above diagram is actually showing the new system I’m going to build, because in my previous system the external storage device was a 2 GB USB stick which meant that the power consumption was even lower compared to a 3.5″ hard disk. I’ll go with the hard drive this time to get more storage capacity and hopefully better stability. I don’t know if this will provide more stability but I’ve had problems with data loss on my previous systems and I know you’re supposed to make some software tweaks on the NSLU2 if you use USB storage with flash memory because of the frequent data write operations. I did make the tweaks though, but time will tell if system crashing is related to flash memory. As operating system on the NSLU2 I use Debian.

The NSLU2 measures 131 x 96 x 28 mm and has 2 USB ports and 1 Ethernet port. The processor inside is a 266 MHz ARM Intel XScale IXP420 with access to 32 MB SDRAM and 8 MB flash memory:

Conversion between USB and 1-Wire can be done with a DS9490 adapter available from Hobby-Boards.com:

The 1-Wire network is connected to a RJ12 telephone connector which means only 6 pins compared to the 8 pins in a standard Ethernet connector.

Somewhere in the 1-Wire network you can connect one of these small 3 pin IC’s for temperature measurements:

This one looks like a transistor but it’s actually a DS1820 1-Wire IC. The power is supplied through the 1-Wire cable. I just use normal Ethernet cable as 1-Wire cable.

If the NSLU2 is placed far away from your Ethernet network you can use a Ethernet to WLAN converter. The WL-330gE from ASUS is even powered by USB:

It is possible to have a long 1-Wire network cable, a long Ethernet cable, or a long mains cable, when you need to connect the system to the rest of the world, which should make it easy to set up the system almost anywhere you want.

This is my old external USB hard disk that I plan on using for storage:

and a small handy two port USB hub, powered by the USB port itself:

I really like the NSLU2 as it gives you a lot of possibilities to make all kinds of fun stuff, but I also realize that it’s getting more difficult to get hold of a functioning unit ever since it was discontinued. If you haven’t got a unit already you should take a look at the SheevaPlug plug computer, or the Arduino project.

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