Think DSP

I am thinking about a new project.  Think Bayes is almost finished, and I have a few ideas for the next book.  One possibility is a computational approach to Linear Algebra.  But the idea I am most excited about for now is Digital Signal Processing (DSP).

I imagine two threads: one is a software-based approach using Python with NumPy and SciPy.  The other is a hardware approach using C/C++ on Arduino.  Since I am more comfortable with the software, I am tackling the hardest part first.  And I am starting with an Arduino-controlled analog synthesizer.

I'll present the design later.  But before I get to the actual synthesizer, I want to start with something I "invented" that might be useful: a cheap and easy way to connect a 3.5 mm audio jack to a solderless breadboard.

There's a $5 solution here: http://store.curiousinventor.com/plug-in-bread-board-stereo-1-8-quot-audio-jack.html

Or you can get the jack for $1.50: https://www.sparkfun.com/products/8032

And a PCB breakout board for $0.95: https://www.sparkfun.com/products/10588

And solder them together.  But if you already have the jack and some break away-female headers, you can make your own solution.  Here's how:

1) Make sure the holes at the top of the female headers are big enough for the pins on the jack.  It looks like they come in at least two sizes:

The ones on the left are too small.  The ones on the right are good.

2) Break off two headers with 5 pins each (or you can make one of them smaller).  UPDATE: after more experimenting, I recommend headers with longer pins than the ones below (stackable headers).  The short pins do not make a good electrical contact with the breadboard, and they do not make a solid mechanical connection.

A few suggestions for breaking so-called break-away headers:  (a) you can't break between two adjacent holes; you have to sacrifice a hole in between; (b) before cutting, use pliers to remove the metal pin from the hole you are sacrificing; (c) you can use wire cutters to make the cut, but you should wear eye protection -- the pieces go flying!  (d) you can use wire cutters and sandpaper to clean up the cut edge.

3) Put the headers into a breadboard and then stack the jack on top.  Four pins go into the back header; one pin goes into the front (so the front really only needs to have 1-2 pins).  Use super glue to hold the whole thing together.

Here's the other side (with the rough edges I didn't bother to sand).

So there it is.  Just a little bit cheaper than using a PCB breakout board, and no soldering.