Equip your Pi for slide and video presentations

It's Show Time

The Raspberry Pi is a fantastic little machine for the price, and it runs Linux without any problems. With only 512MB of RAM, however, running an X Window-based desktop, LibreOffice Impress, and a live video feed certainly exposes the Pi's performance limitations. That's not a bad thing, because the little powerhouse is definitely up to the task. Some things will just take a little longer than on a dual-core 2.27GHz notebook with 4GB of memory. Next, I'll describe my process for getting the machine ready for a presentation.

Make sure the HDMI, power cables, USB hub, and camera are plugged into the proper ports. If you put your Impress slides on a USB stick, you can remove the WiFi adapter from the USB hub to decrease the computational load on the Pi. Boot up the Pi and log in to the graphical desktop. Click on Desktop  1 and start GUVCView:

pi% guvcview

The video feed from the camera will soon appear in a new window, along with an additional GUVCView control window. Right-click on the control window, choose Desktop, and switch it to Desktop  2. Reposition the feed window to a convenient place on the desktop.

I tried using 800x600 resolution (for the video feed) at 30fps, which introduced a little bit of video lag and gave a crisp clear picture. I like the 1280x800 at 20fps size. Although there's a noticeable lag in the video feed, it's fine for static images of parts and PC boards. This window size fills about 60 percent of the projector screen. This setting will probably be the normal resolution during my talks, because it is big enough for people in the back of the room to see clearly.

Next, start LibreOffice Impress on Desktop  1 and open a slide presentation. Select Slideshow from the top menubar and hit Start from first slide. The first slide should fill the screen. Use the Alt and Tab keys to briefly switch back to the LibreOffice Impress main screen; then, right-click and move the screen over to Desktop 2.

Likewise, move any terminal windows to Desktop 2 as well. The idea is to arrange the windows so a simple Alt-Tab will flip back and forth between the video feed and slide show windows. Desktop 1 should only have the video feed and slide show windows. Figure 4 shows how Desktop 1 might look.

Figure 4: The view from Desktop 1.

Everything else goes over to Desktop 2. Figure 5 outlines the remaining windows. Ah, the joys of multiple desktops.

Figure 5: Background windows, such as the video controls and Impress user interface, go on Desktop 2.

Loading Impress takes a little time. Switching between GUVCView and slides sometimes takes a little while, too. When using GUVCView and Impress together, slides with lots of graphics take anywhere from 10 to 30 seconds to load. Load times are minimized by reducing the number and size of graphics on a slide. You could also build the time delays into your talk: Do some commentary while loading the next slide. A little practice will help you make the transitions smoothly.

Next Steps

In my case, the view of the electronic parts was best when I put the camera between 3-1/2 and 4 inches from the object. You'll want to experiment with the distance to the objects and focus depending on the nature of the image you'll be viewing.

I didn't have a mounting bracket to hold the camera when I wrote this article, and I'll definitely have to engineer one before I do my next big talk. It might also make sense to add a few cheap, white LED lights to illuminate the parts. I'll also have to package the Pi, the USB hub, wires, and so on into a nice box, so it's easy to set up at the venue. Figure 6 shows the components neatly bundled together.

Figure 6: All the components in a tidy bundle.

Automating the startup process, loading a slide stack, and bringing up the camera could be handled with scripts.

So, there you have it – that's how you build your very own Raspberry Pi presentation machine!

The Author

Rob Reilly is an independent consultant, engineer, writer, and speaker. He provides expertise for private-sector companies on Linux/Open Source/Open Hardware, DIY/Maker Movement, business analysis, and tech media projects. Contact him at robreilly@earthlink.net.

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