Monday, December 31, 2012

Mounting the Pi's

By far the easiest part of the project to bring a dozen or so Raspberry Pi's online was finding a place for them to stay in one location. Rather than going with a Lego approach, I decided to obtain an acrylic sheet (plexiglass) from the Home Depot (SKU: 241610) and mount the Pi's on there.

There were a few reasons for that choice:
1) Plexiglass is cheap and easy to obtain
2) With a simple drill (Dremel-type), it is easy to drill the right size holes in it
3) It doesn't break easily
4) It looks nice

The disadvantage is that standard plexiglass is rather flexible. I expect that, once we are fully completed, I'll need to reinforce it somehow.

The Pi's come with two pre-drilled holes in the circuit board that can be used to mount them  perfectly. I decided to use Radioshack stand-offs (#276-195). They come in packages of four, and include two screws per standoff, which translates to two RPi's per bag. Without crowding the plexiglass board, 14 Pi's easily fit on a 18"x24" board.

Since my goal is to network the Pi's and to power them as well (duh), I decided to mount the top row of RPi's with the SD card facing down and the bottom row of RPi's with the SD card facing up. The means that

a) power is on the inside of the board
b) SD cards are on the inside of the board
c) Network cables are on the edge of the board.

Labeling is an important thing to keep in mind, since the RPi's all look the same. After mounting the first set, the board looks like this:

Note that my idea was that I was going to power the boards via a USB hub. According to spec, each USB port must be able to provide 500mA of current, which I believe to be enough. It turned out very quickly that this was not the case, and I'll elaborate on that in a later post. Suffice it to say, the USB hub is no longer part of the design.

Anyhow; after also mounting the bottom row, adding network cables and a few switches, the whole thing looks like this:

Note the two zip-ties that keep the cable mess together on the board. When we come closer to finishing up, I'll make sure that the network cables are all of the right length, the same color, etc. The eye needs to be pleased also, after all.

In a next post, I'll cover getting power to the board.

Next: Power requirements of the Raspberry Pi Model B

Sunday, December 30, 2012

Project initiation

After experimenting with a single Raspberry Pi, I came to the conclusion that the units form a cost-effective platform to give undergrad students a dedicated Linux node for the duration for a semester. They'll have full superuser access in an isolated playground, and they can access the machine whenever they feel the need to do so.

To take a simplistic view of this, I'll need to solve two problems: hardware and software. Hardware appeared to be easy. Simply order however many units you need, find something to mount them on and power them up, and tie everything in to a network switch. It turned out to be a little more problematic than that, but none of the things that I ran into proved to be insurmountable.

I started out with ordering 15 boards, and they came in a nice small package.

For my project, I was able to get the Model B Raspberry Pi's that come with 512 MB main memory and
with on-board 100 Mb/s network jacks. Earlier in December, MCM electronics had plenty of Pi's in stock and was able to get them out quickly. If you're looking for a Pi and cannot find any, it is worth checking them out.

Next: mounting the RPi's

My Raspberry Pi experiment

(cross-posted from my Information Security Leadership Blog)

I ordered a Raspberry Pi a while ago to tinker around with. I did not have a fully developed plan for what to do with it yet, but a fully functional computer for $35 is something that I couldn't pass up. Now that I have messed around with it for a while, I'm really starting to like the device. Eventually, it will probably make a nice media center of sorts, but 512 Mb of on-board RAM is plenty to run a modern (headless) Linux distro and plenty of useful software has been ported to the platform.

As you know, I regularly run classes in which students participate in a virtual cyber wargame. That game typically involves about a half dozen targets, serving different purposes Some of the limitations that I experienced in the past were constraints on the number of VMs that I can bring up, and the fact that I cannot give my students their own individual machines.

With Raspberry Pi's, that  might change; there is really nothing wrong with provisioning one RPi per student. I'll need  a cheap network switch to power them all and  punch of power supplies and/or a USB port replicator that can provide enough current for the boards. They'll still be behind some form of a bastion host, so I don't have to have a top-of-the-line switch; something cheap(ish) will do just fine.

The guys over at Pwnie Express have put together a nice bundle of security software for the RPi that  might just serve my purposes very well.

It is worth exploring!

New blog: Technology Toolshed

I started blogging about my experiments with Raspberry Pi computers on my Information Security Leadership blog. However, since hardware tinkering and Information Security Leadership are only slightly related (at best), I have decided to spin my technical musings off to a separate blog. If you are interested in what I am doing in hardware land, please subscribe to my Technology Toolshed blog.