Signals

Since I recently bought several new guitar pedals, I decided that I needed a new pedal board design. My old design was a simple one: suitcase with velcro and well placed cables.

Old Design

I’ve also been trying to find an excuse to learn Solid Works for creating 3D models. Thus, I decided to create a Solid Works model of my new pedal board design, shown below.

Pedal Board Front-Side

… and the back side… showing the triangular supports…

Pedal Board Back

The two large red blocks represent the Ernie Ball volume pedal and the Cry Baby Wah-Wah pedal. The smaller blue blocks represent traditional Boss and MXR pedals. I’ll be cutting the boards for the triangles and the long boards later this week!  I’ll probably end up staining the boards to bring out the knots in the wood.

The first paper where I was the first author has finally been posted to IEEE Xplore’s website. The paper was titled “An implementation of ROS on the Yellowfin autonomous underwater vehicle (AUV).” You can find the Google Scholar reference to my paper here:

http://scholar.google.com/scholar?hl=en&q=An+implementation+of+ROS+on+the+Yellowfin+autonomous+underwater+vehicle+%28AUV%29+&btnG=Search&as_sdt=0%2C11&as_ylo=&as_vis=0

I presented the paper at the IEEE / MTS Oceans 2011 conference in Kona, Hawaii. Designing underwater robots has its perks!

I recorded this piece using my new Tascam Linear PCM Recorder. I recorded the finger picking section first, then I overdubbed the lead part using the Tascam recorder. I didn’t use any computer recording software and I didn’t mess with the EQ at all on the tracks. I’m pretty impressed with the sound quality and the microphone.

1,016 Miles by Kevin DeMarco

Avnet / Xilinx Microboard with Motor Control Circuit

I’m getting pretty far along on the wearable system I am building for my Real-Time and Embedded Systems class. I now have the Xilinx Microboard driving two DC motors to give the user feedback on suggested paths. I embedded a Microblaze 32-bit processor in the Xilinx FPGA which uses the lwip Ethernet stack to communicate with the Gumstix Overo Air COM over a telnet-like interface. Given the appropriate command, the FPGA sends an enable signal to the OpAmp / MOSFET circuit to drive the DC motors. Hopefully, I have all this integrated in a couple weeks when this is due. I will put up a full project page that will go over the problems and tribulations I’ve encountered with the Gumstix and Xilinx / Avnet Microboard at the end of the Fall 2011 semester.

Microboard with External Circuitry

Mira and I adopted a new stray puppy, who we have named, Ponce.  He is a Labrador / Hound mix and he is great with our other dog, Jacy.  Here is a great photo of Ponce.

Here is the flickr photo stream of my trip to the Robotics Science and Systems 2011 at the University of Southern California.

The full flickr photo stream can be found at: LA-RSS-2011

Here is a quick video I put together of my dog, Jacy, playing in the sand on the Atlanta Belt-line. I put the video together using some generic iMovie transitions, sue me.

Here are some photos of Jacy from this summer, so far!  We have gone swimming in the Chattahoochee river, walking through trails, and Jacy is great at listening now.

I am working on a dynamics simulator for an underwater vehicle to be run in the Robot Operating System (ROS – www.ros.org )  The purpose is to be able to completely simulate an autonomous underwater vehicle (AUV) in ROS and then use that same code to control the actual AUV in the water.  Obviously, a variable switch will be used to designate whether the software is running a simulation or actually being tested in the water.

I am using the Boost odeint library ( http://svn.boost.org/svn/boost/sandbox/odeint/ ), which unfortunately, required a manual install on top of the regular Boost libraries.  Odeint is really quite easy to use, almost as easy as Matlab’s ode45 and Octave’s lsode ordinary differential equation solvers.  In ROS, I have the simulator loop at a specific rate (ie. 10 Hz) and I only have the ode solver compute one step every loop.  I ran into trouble using the Euler step method with a slow loop rate, but either increasing the loop rate or using a better ode algorithm (ie. stepper_rk4, stepper_midpoint) resulted in proper results.  In order to test my basic setup, I simulated a pendulum swinging back and forth.  Here is a screen shot of the pendulum simulation in Octave…

Octave Pendulum Simulation. Top plot is pendulum height, bottom plot is pendulum velocity.

I compared the Octave simulation, which I know is valid, to the ROS simulation of the pendulum, which is shown below.

ROS Pendulum Simulation. Top plot is pendulum height, bottom plot is pendulum velocity.

Now I just have to figure out the differential equations for the underwater vehicle’s motion and I will be able to simulate that in ROS as well.

I recently purchased a the AKAI APC20 for my Ableton Live setup. When I was at the music store purchasing the controller, the guy at the counter suggested that I purchase the $15 store warranty. However, I declined since I figured that if I wore out the pads on the controller, it would warrant buying a higher quality controller and in a year a newer one will be out anyway. Unfortunately, when I got home I discovered that one of the pads was already acting strangely! It would get stuck and it didn’t have the same feel as the other pads. I was in a dilemma: drive the 30 min back to the store, or take apart my brand new APC20. Take it apart!*

*Disclaimer: This will probably void your warranty, so don’t do it =)

I actually took the APC20 completely apart before taking a photos, so even though I am going to display the photos backwards, as if I am taking it apart. Time warp.

AKAI APC20 - Before Tear Apart

First, remove the 12 visible screws on the back of the APC20.  Then, the 4 rubber feet have to be removed.  The rubber feet are held onto the APC20 with a combination of two-sided tape and the rubber stoppers have little plastic pieces that fit into holes.  Thus, you can remove the rubber stoppers without having to re-glue them back on later. I like these rubber feet.  Remove the screws under the rubber feet as well.  You DO NOT have to remove the silver hex screws that are visible from the front.

The Rubber Feet pop off just nicely.

The APC20 cover will then come apart quite easily from the back of the APC20, BUT! be careful you don’t break any cables that are connected between the front and back panels as shown in the next image.

After removing the cover.

At this point, you have to remove the screws that connect the PCB to the back panel.  There  are quite a lot.  Most chips these days have great ESD (electro-static discharge) protection, but make sure not to run around a carpeted room while pushing your finger onto any of the parts.  Also, there are two screws that are slightly hidden under the ribbon cables.  These are used to remove mechanical stress on the ribbon cables.  Next, you will have to remove the Cue Level potentiometer and level selector knobs.  These pop off really easily.

Pop 'em off!

Also, you will have to remove the washer under the Cue Level potentiometer.

Remove the washer!

At this point, you should be able to remove the PCB from the back panel.  If the PCB gives you any resistance, then you probably missed a screw.  Be careful.  Once the PCB is out, the pad is now visible.

The AKAI PAD in all its glory.

Very Bendy!

Front side of PCB

After I had taken the APC20 apart, I discovered that the capacitor displayed in the next photo (the larger left one) was the offending part.  It was interfering with the operation of the pad.  To fix this, all I did was move the capacitor slightly away from the pad, problem fixed!

The capactor was the problem!

When replacing the pad, take the time to really smooth it out!

APC20 Front Panel Only

USB Chip, power regulators, & microcontroller to process button presses.