Brackets, Brackets Everywhere

Brass goes hand-in-hand with copper when building steampunk gadgets. I used 3/16-inch thin-wall brass tubing, along with 1/8-inch-thick by 1/4-inch-wide flat brass stock to build the mounting brackets for the Rasp Pi, LCD screen, video driver board, speakers, audio amp, and battery. My trusty antique 100/140-watt Weller soldering gun worked well for bracket construction.

Brass is very easy to solder with rosin-core solder and is a key reason I like using it in steampunk devices. You can cut the brass tubing with the same plumber's tool used for the copper tubing. The flat brass stock is easily cut with either straight aviation tin snips or a Dremel with a cut-off disk. I used a sanding disk on the Dremel and a sanding sponge for edge smoothing.

I also fabricated a spring-operated latch on the front to hold the keyboard in place (Figure 5). A fixed bracket protrudes from the left front of the case to hold that side of the keyboard. A couple of speakers are mounted facing toward the front and slightly behind and on either side of the LCD screen. The brackets are attached to the LCD frame. Interestingly, the open space frame design gives a pleasant 3D effect to the sound from the speakers.

Figure 5: A spring-loaded latch holds the keyboard cover in place.

Right behind the LCD screen is the video driver board mounted on its own bracket (Figure 6). The video board runs on a direct 12V line to the power board; it has HDMI, VGA, and composite inputs, and it uses a short HDMI to micro-HDMI cable to hook the board to the Raspberry Pi. A second, very short micro-HDMI to HDMI adapter cable connects to a longer cable for any optional external monitors.

Figure 6: The video board and bracket behind the LCD.

Talk About Power

The lunchbox can operate in two different power modes. Most of the time it's hooked up to a 12V, 1.0A generic wall wart repurposed from an old network router with roughly 12W of power capacity. Measuring the consumption with a Kill-A-Watt meter showed the machine used about 11W in normal desktop operation. It idled back to 5W when the screen was blanked.

An on-board 15,000mAh super polymer lithium ion battery connected to the main power supply board sits in a bracket at the bottom of the lunchbox frame (Figure 7) and is charged through the 12V wall wart when the Rasp Pi isn't running. A larger capacity wall wart could be used if I needed to charge the battery while also running the Pi.

Figure 7: The battery and internal brackets.

The power supply board has a pair of 12V to xV (up to 3A output) regulators on a small piece of phenolic circuit board. Outputs are selectable by jumpers for from 1.8 to 12V. A female socket on one end connects to the battery. I used a common + /- input power bus setup for ease of future expansion. One regulator supplies a dedicated 5V to the Raspberry Pi. The other regulator is for the steady 12V needed by the audio amplifier board. The color LCD driver board connects to the 12V power directly from the wall wart or battery input power bus. The speakers are powered by a 10W per channel stereo amplifier board with a standard aux cable running to the Raspberry Pi analog audio port (Figure 8).

Figure 8: The audio amplifier board and bracket.

I plan on adding a switchboard to control all the hardware modules individually. For example, when booting everything at once on the battery, the audio board doesn't initialize correctly because of high current demands. Switching it on after the Pi boots up eliminates that problem. Plus, if I'm not going to listen to audio, the amplifier can be turned off to conserve battery power.

Software

The first piece of software I always load onto my Linux machines is the Synaptic package manager [3] for installing software; apt on the command line works well, too, particularly for regular software updates.

As mentioned earlier, I use the luvcview tool [4] for viewing the video feed from the Hedley's JeVois smart machine vision sensor, which uses neural network algorithms to recognize 1,000 different objects; it superimposes a box around objects at 30 frames a second and provides a real-time data stream of recognized object names and XY coordinates, so you can track faces or things and perhaps move servos on your robot. I've found luvcview to be much more reliable than guvcview or other camera applications.

LibreOffice handles all the office-type jobs you'll ever have on a notebook. I mostly use the Writer word processor and Impress presentation manager. I wrote this entire story with LibreOffice on the lunchbox. The only thing I don't like is that, while touch typing, the mousepad sometimes picks up my trailing right little finger movement when pressing the Delete key. That usually moves the cursor somewhere unexpected, and I end up mistakenly deleting a word or paragraph. I'll have to train myself to cross the left-hand index finger over for deletes.

Overall, I can load just about anything on the lunchbox and it will function properly. It even runs exotic programs like gqrx for software-defined radio listening.