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audio cadpreviewI would be happy to get this hamster moving, but I really want to go ahead and tackle the audio part of the project. It's also the heaviest part so I need it to be low in the body. In the picture on the left I have the plan. This tier will include: a pair of generic brand 4" automotive speakers, Adafruit's 20W Class D Amplifier, Robertsonic's WAV Trigger, and my own custom audio power & communication distribution circuit.

There was a different plan at first that I almost did not tell you about ...


Xeekworx Custom Audio Mixer


Robertsonic's WAV Trigger

The Robertsonic WAV Trigger (left) has been on back order several times since I started the project and believe it or not this is the only device I could find that has polyphonic support (play multiple sounds simultaneously). 

The programming was a bit complex and after a couple of weeks it laboring, it worked! The biggest mistake I made was assuming the Teensy had the same input voltage tolerances as a typical Arduino; it doesn't. I put 9V through this Teensy on several occasions and eventually it gave up from overheating.I was eager to change that and develop my own sound mixer (right) using a Teensy 3.1 and Teensy Audio Adapter

So back to Plan A (The red board on the left). I had to buy the Robertsonic WAV Trigger just as soon as it was available! Fortunately, the WAV trigger uses serial communication just as my custom sound mixer did, so i didn't have to rewire things and also the programming for the Arduino would remain close to the same. The actual sounds will be stored on a micro SD card that plugs into the WAV Trigger.



Adafruit's Stereo 20W Class D Audio Amplifier

The WAV Trigger does have some amplifier capabilities, but it's not going to be enough to power my planned 4" speakers. I want to at least be able to fill a room with sound and there's no telling how soft it may end up being inside the sphere. For this I chose Adafruit's Stereo 20W Class D Audio Amplifier. It also has volume control via TWI (I2C) so I'll be able to adjust the volume using a remote control.

This amp can also handle 12V so I intend to feed it that if I can later on to get the most out of the speakers.




Scosche HD4003 4" Speakers


The sound board and amp were the more difficult decisions, but the speakers should be pretty simple. I just walked into my local Walmart and purchased the cheapest smallest speakers I could find. That ended up being some Scosche HD4003 4" 3-Way Speakers. They actually sound really nice when I give them as much juice my amplifier can tolerate. They were only $20 (USD) and I know I could have found some cheaper online, but I was eager to get all of this hooked up and I just so happened to be in Walmart. They're actually larger than I wanted, 3" was my target size.



To distribute power to the amplifier and sound board I needed to build a custom circuit. 

audio power distribution

This is my first attempt at creating my own circuit board using spare wires laying around for the traces. I also decided to put headers on the board for I2C, Serial, so that I could extend the distance these wires had to go. I'm really not happy with this board, since it was my first, but it works and it'll do until I can make a version 2.

Power comes in the large blue screw terminal and splits off in parallel to two JST connectors. Then from the JST wires to the amplifier and WAV trigger. On the right side of the board are connections for Serial and I2C which gets routed to the Arduino that will be in the tier above this one. There are additional headers where also two pins connect directly to a JST connector, but these aren't used. I originally intended to power my custom audio mixer from the Arduino above, but that never panned out. I also added a blue led so I knew if the audio components were getting power, this comes off in parallel as well from the blue screw terminal.

How am I going to power this board? Well, that hasn't been decided yet. There will likely be a main power distribution circuit above this tier where power from the batteries come in. We'll get to this part later. For now I have enough setup to start testing the audio!



Mounting everything was a challenge and I had to be very creative when designing the mounts for the speakers. I wanted the speakers to angle slightly upwards and the components needed to come out easy for maintenance.

The speaker mounts took the most time and were difficult to print. They were printed face down and supports were used. The picture shows an earlier version of the speaker mounts, but most of the difference is the vent openings which are just to save on plastic and weight.

Each component has it's own custom mount that I designed and 3D printed. These mounts then screw onto the teir. I like this design, but next time I'll probably make the bolts more accessible and add recessed areas for the nuts to go underneath so I don't have to use plyers to tighten eveything down.

 audio mountedaudio speakermount1audio speakermount2
In the next update I'll be working on the Main Power Distribution Circuit and decide on how I'm going to get to 12V!