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A Simpler/Better Rar Box 
5th-Oct-2009 11:27 am
Sneaky Scabrous
A recurring theme that I’ve posted about here is the quest for a “rar box,” a device that’s small enough to hide in a costume that could be used to play back monstery sound effects. A previous post mentions the Adafruit Wave Shield, which was a pretty good solution (video of it in action) if you’re comfortable with a fair bit of soldering and a little bit of programming.

SparkFun Electronics now sells a unit called the MP3 Trigger which is a slightly less daunting version of the same idea. If you can solder just a few trigger switches, everything else has been taken care of. You load up a MicroSD card with a few MP3 files (named TRACK001.MP3, TRACK002.MP3…through TRACK007.MP3), and each sound will be automatically triggered in response to a closing of the corresponding switch.

Pros: No programming required. Slim, single-board design. A few dollars cheaper than Arduino + Wave Shield combination. Less soldering. Better sound quality (16-bit MP3 vs. 12-bit WAV). Stereo sound; with clever placement of speakers and corresponding careful sound design, you could have audio effects emanate from different parts of the suit (e.g. put the “left” speaker in the muzzle and the “right” speaker under the tail, then design the sound files with roars and yips only using the left channel, and fart noises only using the right channel).

Cons: Limited to seven triggered sounds (tech-savvy types can trigger up to 255 sounds with an external microcontroller, though this negates much of the simplicity). Less flexible triggering options; mostly limited to momentary pushbuttons, other switch types (e.g. magnetic Hall-effect sensors) may require some changes (or again, a separate microcontroller).

In either case (Wave Shield or MP3 Trigger) you still need to add some stuff:
  • A FAT16-formatted SD card (Wave Shield) or MicroSD (MP3 Trigger) to hold the sound files.
  • Amplified speaker(s) to play the sounds (various portable iPod speakers work great for this).
  • 9V battery to power the board.
  • A sweat-proof enclosure for the device and battery.
  • Trigger switches and wire (see the “in action” video above for an example).
Neither system is capable of polyphony; they can play only one sound at a time. With the MP3 Trigger, a new sound triggered will interrupt any other sound currently playing. With the Wave Shield, since it’s Arduino-controlled, this will depend on how you program it — you can either interrupt the currently-playing sound, or not allow other triggers until the sound has finished playing.
5th-Oct-2009 08:19 pm (UTC)
It's contagious. I read the end of that first sentence as "monastery sound effects". Gregorian chants?
6th-Oct-2009 11:25 pm (UTC)
haha me too! XD
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6th-Oct-2009 04:15 am (UTC)
Well that's sort of the handy thing with the MP3 Trigger...if seven sounds is enough, you really don't need to mess with microcontrollers at all. Unless you want to anyway. They're kinda fun. Rar.
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6th-Oct-2009 05:34 am (UTC)
Indeed, it took me a couple of years to get up to speed...but then I was naively starting from the wrong end (Microchip PIC, bare chip, assembly language, using a Mac). If you haven't already, take a look at the Arduino board, and there's a little $12 getting started book published by Make/O'Reilly (there's even an ebook version for iPhone too). There are plenty of more capable microcontroller options out there, but in terms of being a sensible introduction for normal human beings the Arduino is tough to beat right now. And then you can add the Wave Shield directly to it and start making rar sounds!
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7th-Oct-2009 12:10 am (UTC)
Yes and no. The book is called "Getting Started with Arduino" and is a vastly expanded (but not overwhelming) version of the info at that site. You can also usually find it at Borders and the like if you wanna take a look first.

As for switches...if you're using the MP3 Trigger, then the keypad wouldn't work. All you need are simple momentary pushbuttons like these (or any other type there labeled "pushbutton," even the big ol' arcade-style buttons!). The MP3 Trigger can handle up to seven of those, but that's it, that's the limit. If you want more than that, you either need to control the MP3 Trigger with a microcontroller, or use a different microcontroller-driven sound effects board such as the aforementioned Wave Shield. In either case then, with just a little bit of programming, you can use a keypad-type device with more buttons.
7th-Oct-2009 01:36 am (UTC)
GOD HOW I WANT THIS. But I am not technically inclined at all. Do you know of anyone who would put it together for me, maybe I could talk ot WolfTronics?
7th-Oct-2009 04:38 am (UTC)
If you happen to be local-ish (I'm San Francisco Bay Area-ish) I'd be happy to help out. Could try to do something remotely, but would need to know exactly what capabilities you're after. Or alternately, yeah, maybe Wolftronix would be into it, this seems right up their alley (do they read LJ rarsuit?)
7th-Oct-2009 11:21 pm (UTC)
Sadly I live in the Corn State, how large would all the equipment be to put in a suit? I already have mine made and don't have alot of room in the muzzle or anywhere else.
8th-Oct-2009 01:11 am (UTC)
The board and battery are pretty small...they'd almost fit in an Altoids tin. And the speakers are roughly cellphone sized (unless you need something bigger & louder).
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