Control Rasp Pi slide shows wirelessly

Regular Raspberry Pi Geek readers might recall my "Presentation Machine" story back in 2014 [1]. There, I described how to set up a first generation Raspberry Pi (Rasp Pi) to show slides, with tips on how to use the device during a show. I've since used subsequent versions of the machine at OSCON, Fossetcon, and the Future of Education Technology Conference (FETC).

Today, I look at the evolution of my current Raspberry Pi presentation machine, the "wired" and brand-new ESP8266-based "wireless" clickers, and how it all comes together on stage. I discuss two different pieces of hardware linked together via WiFi, and in a flash of inspiration, I even add a Steampunk theme to the apparatus, resulting in very positive feedback from audiences.

Presentation Machine

The latest Steampunk Presentation Machine is a Rasp Pi 2 model B (RPi2B) [2] running the latest version of Raspbian Linux with a 32GB Samsung Evo+ microSD card, an Edimax USB WiFi dongle, a Logitech wireless keyboard/mousepad, and the original Logitech C270 webcam (Figure 1). The Rasp Pi is mounted on a frame made out of brass tubing, and an aluminum arm positions the camera. The camera was removed from its original housing and mounted in a custom brass and copper frame, giving it a retro-industrial look (Figure 2). The whole works are mounted on an old piece of laminate flooring.

Figure 1: Steampunk presentation machine.

Figure 2: Hacked webcam.

Wired Clicker

The terminal block next to the camera arm connects to a 10-foot (3m) length of re-purposed CAT 5 cable and my "wired" clicker buttons. The other side is attached to a couple of GPIO pins on the Rasp Pi.

Steampunk is typically over the top and very visual, so I reasoned that a little two-button clicker wired to the Presentation Machine would add dramatic effect to my talks. It did. Instead of carrying around a keyboard during a presentation, I just push the Up or Down button on the hand-held clicker (Figure 3) to move through the slides. Audiences like it a lot.

Figure 3: Wired clicker with two buttons.

A short Python script runs on the Rasp Pi that reads the state of the two buttons and initiates a system call to the xdotool command [3]. Xdotool, simply imitates a keystroke. Pressing the Up button outputs the code for the Up arrow key. Likewise, the Down button imitates a Down arrow key. LibreOffice Impress catches those keystrokes as if they were coming from the keyboard and changes the slide accordingly.