Saturday, September 6, 2014

Sound Systems for Jawas and Tuskens

 From Greg... 

This document describes the construction of sound/voice systems for our Jawa and Tusken Raider costumes.  The basic components of each are a Robertson MP3 Trigger (available from SparkFun) and a 16W Aker amplifier (popular with TK’s and available on Amazon.  There are cheaper options than the Robertson Trigger, but it has some capabilities that are hard to match.  In particular, it has 18 external trigger pins, each of which can cause a different action, including playing a specific MP3 track or selecting a random track from a set.  It has a slot for a microSD card that contains the MP3s, and a small initialization file that specifies the response to each of the 18 trigger inputs.   

For the Jawa, I have one input that causes it to play the Jawa blaster noise, one that plays ‘Utinni!’, and one that plays one of a set of random Jawa sounds.  (The Tusken is simpler, with only one input that plays the Tusken warcry.)  The MP3s themselves I found on the Internet somewhere, but I have zip files of the contents of the microSD card for each of the Jawa and Tusken.

My first version of the Jawa sound system was an unmodified Aker amp with the output of the MP3 trigger being fed into the line-in jack.  The MP3 trigger was powered with a 9V battery.  I had soldered a male header (one of these) onto the MP3 trigger to make it a bit easier to attach and detach trigger switches.   

 Robertson MP3 Trigger with header soldered onto left-side trigger contacts.

Then I taped the MP3 trigger board and the battery to the side of the Aker amp and the Jawa wore the whole thing under his robes, hanging from the neck strap.  For controls, I soldered three normally-open pushbutton switches together and encased them in a palm-sided bit of Sugru as shown here.

Jawa controller.  Three pushbotton switches embedded in random-color Sugru.  

 The wires from these switches were fed up the Jawa’s sleeve and attached to the appropriate leads on the MP3 trigger board.  WRT circuit details, the outside contacts for each of the 18 triggers are common, so a single wire will do for those.  So for 3 switches, I needed four wires.  I wanted to be able to disconnect/reconnect the controller easily, so I used RJ-45 (phone jack) connectors.  This picture shows the Trigger board with the board-end connector installed and wires attached to trigger pins 1, 2 and 3. 

Robertson Trigger with controller jack added.

This first version worked fine, when it worked.   It was awkward because turning it on required plugging the 9-volt into the MP3 trigger board and separately turning on the Aker amp and setting the volume.  It was a bulky thing sitting on the Jawa’s chest and you could see the red glowing LED on the Aker amp through the robes.  Adjusting the volume required reaching in through the robes, and wires seemed to come undone with some regularity.  When that happened it was never quite clear if the problem was with the audio connection, power to the MP3 board, loose trigger wires or something else, and it usually required undressing the Jawa to find out.  Not the end of the world, but not ideal either.

For version 2 of the sound system (version 1 on the tusken) I was determined to do better and to shoehorn the sound system into the bandoleers that each wore.  I started by disassembling the Aker amp into its basic components: the rechargeable battery, the speaker, and the board that contains the circuitry.  Some bandoliers are pretty small, but I found these: Ammo Pouch, 2 Pocket, Leather, Yugoslavian Issue that looked big enough to do something with.  The speaker from the Aker amp is pretty large, so I found a 2” diameter replacement speaker, keeping with the 4 Ohm impedance here.  The idea was to distribute all these different components into different pouches in the ammo belt/sash.  So, sort out what will fit where.  Disconnect the Aker speaker and cut the custom connector from the end of its wires.  Install that connector onto new wires attached to the new 2” speaker (make leads long enough to reach the Aker board. 

‘2” speaker with leads and original Aker connector

Cut the leads between the Aker board and the rechargeable battery if necessary so that they fit in different pouches. 

 Aker Battery with leads extended

The final bit is the MP3 trigger board.  I wanted to get rid of the separate 9V battery that I had powering this board.  I achieved this by poking around on the Aker board until I found a point that was just on the other side of the main switch.  I.E. it was unfiltered battery power, but only connected when the Aker board had been turned on.  Tapping into this voltage to power the MP3 trigger would mean that I could eliminate the separate 9V, the MP3 trigger would automatically get turned on when the Aker was turned on, and we’d be leveraging the (relatively large and rechargeable) Aker battery.  This was a win on all counts and has worked beautifully.   The power tapping is shown on the figure below.  The right-most end of the read wire taps appropriate positive voltage from the Aker board.  The bottom-most end of the yellow wire attaches to the ground side of power.  Both are fed into a 5.5mm/2.1mm center positive barrel jack with leads long enough to power the Robertson MP3 trigger. 

 The next pictures show the electronics components laid out before insertion into the ammo pouches, after insertion, but the with pouches open so you can see how it fits and lastly of the final assembly.  I did trim the leather a bit in non-visible places so that the wires would tuck nicely. 

The Jawa sound system is very reliable, runs for hours without recharge (really don’t know how long, I’ve never run it out of juice) and fits nicely in a 4-pouch bandoleer.  It can be turned on, volume adjusted or recharged simply by opening the top of the pouch that contains the Aker main board.  The other pouches stay closed.  For the Tusken, I squeezed a bit harder and got all of the components into a single two-pouch unit.  Generally I’ve worn this as an across-the-chest bandoleer, but it’s heavy and doesn’t necessarily hang well.  I’m considering switching it to a waist bandoleer in the future.

Greg Eisenhauer

No comments:

Post a Comment