Easy Halloween Sound Hack, Part One

My aunt and uncle set up a "Haunted Forest" every year, where they take area kids through a section of their woods with groomed trails and various scary things. This year I'm helping "up the ante" with sound, lighting, and robotics (pneumatic and/or otherwise depending on time). I'll cover various means of tech-ing up the fear.

The first hack is pretty straight-forward, the only possible glitch being sound file format conversion (the board I'm using doesn't support MP3) to OGG. WAV is supported (and desirable under some conditions) but the storage space is somewhat limited, so I'm using mostly OGG except for when sounds are being looped or played sequentially. The compressed format introduces a small, but perceptible, delay under those conditions.

My test rig was designed to be cheap and mutable, so I used a mono amplifier (Adafruit ID 2130) and the mini sound trigger board (Adafruit ID 2342, 2M flash storage), about $19 altogether. There's an integrated version (2M flash, stereo amp) that I might consider, it's about $25. I'm anticipating we'll use anywhere from 2-6 of these across the forest, with a variety of triggering mechanisms.

Breadboarded prototype; cheap version

The Adafruit docs detail how the device works. Nutshell: sounds are triggered via either the board's GPIO pins (pull to ground) or serial port. Only one of these mechanisms can be used at a time. (I have another project using serial control; this will be documented later.)

For the haunted forest (and my own display) we'll need several triggering options, including PIR, simple switches, and possibly audio. Trigger pins will be externally exposed via a simple jack, probably 1/8" audio. Speakers will be external with an option to stick it onto the project box.

One obvious usage is to hang the box from a tree with the PIR firing down, or towards the path. For extra giggles you could either point it so it fires after the victims have passed so the sound comes from behind them. With only minor effort, and separated stereo speakers, you could set up a sequential trigger that first comes from behind, then in front of, the victims, etc.

For my own Halloween display I'll be using two setups, one with a PIR for people approaching the house, and another at the house for when they dip into the candy bowl. With a 4 Ohm speaker the sound is more than enough to raise a hackle or two, although if you need to project over a distance you'll want something more powerful than the 2.5W amps shown here or on the integrated device.

Upcoming posts will detail the lighting (fire and lightning effects, other simple things), any robotics, and the integration of all these systems into a unified pee-inducing system.

Electric Imp + OLED + ... Squirrel?

The Electric Imp came out before the days of essentially-free ESP WiFi modules. It was designed to be embedded into devices, provide a WiFi interface, and some basic cloud connectivity. It's a bit of an odd duck: it's initialized by blinking lights, e.g., seizure-inducing screen flashes from your phone. This is a pretty unique way to get things set up, and it works great.

I had a few of these devices sitting on a shelf and recently ran across someone asking for help connecting them to a small color OLED with an attached SD slot for image storage. While I waited for my OLED to arrive I decided to hook it up to one I had on hand, a 128 x 64 monochrome OLED, hot on the heels of hooking up a different 128 x 64 monochrome OLED to an Arduino as part of another project (project blog(s) coming soon pending blogging platform change).

Not quite there yet; image buffer not written to OLED.

Both the monochrome OLEDs are based on the SSD1306 display driver. I wired the display to the Imp using SPI, but as the project requirements morphed, I realized the Imp dev board the project used, the April, didn't have the IO necessary to use SPI since we still wanted user input under Imp control. The next iteration will hook up the display using I2C. The caveat is that the OLED that'll actually be used, while I2Cable, will require a fair amount more effort to ensure access to both devices on the board, the OLED, and the SD card.

The final SSD1306 library combines to existing code bases: the first an Imp-specific Squirrel-based class optimized for image display under I2C (e.g., not pixel-oriented line drawing), the second the Adafruit SSD1306 library with line primitives supporting both I2C and SPI.

The end result is a new Electric Imp SSD1306 I2C library. I may continue development to support both I2C and SPI; the SPI data writes are faster, but exhausts the resources of the April board (an "imp001 device"). Since this is a bespoke project I decided to keep the original library small, focused, targeted at the project's exact needs, and over-documented. I will likely robustify this effort into a general-purpose Imp SSD1306 library.

Now we're cooking with gas: I can haz pixels!

The images above are with the original SPI wiring. The next episode will include a more in-depth writeup discussing the library itself, the I2C wiring with additional input (and output?) devices, a link to the library, and will include how to access the Imp from a phone and do something with the attached devices.