Ok, so that was a couple years ago, but it's still awesome, and it's great to see the SX-150 being used as a real instrument. I still think it's pretty hard to control with just the stylus and a sequencer gives you more to work with, but this is pretty awesome.

Back again with the next phase in the Arduino-based sequencer for the SX-150 project. Boy, I need a catchier name for that. I'll work on that.

If you recall, at the end of Part 1 I had used a digital potentiometer to replace the stylus-and-strip control for the Gakken SX-150 Analog Synthesizer.

In this next stage of the project, I'm going to replace the digipot with one that has a wider range, then extend my circuit and my source code to let the arduino directly play individual notes without having to worry about resistance values.

I know, I know, there are a lot of those out there. Well, that's half true. There are a lot of calculators that will take the resistor & capacitor values and tell you what the resultant timing would be... but usually you start from the other direction... you have a timing spec in mind and you need to know what components to use. That's how I tackled it.

You tell it that you want the timer to fire every 60 seconds, or at a frequency of 440Hz, and it will make recommendations about some common components that will have that effect, along with duty cycle, etc.

Because my blog software doesn't like adding javascript very much, I put the calculator on it's own separate page: http://totusterra.com/555timercalc.html

Hopefully this will be useful to anyone playing with the 555, with or without the Arduino involved.

Out of the gate with the first blog post of the new year, and this is one I'm particularly excited about because it gets me to the point of starting to hack things that make cool sounds. I've long had an interest in experimental electronic music, so I'm excited that I have something to share in that arena.

In the past I've mentioned my wonderful wife (who is wonderful, if I didn't say so), and this Christmas she doubly earned that distinction by buying me a Gakken SX-150 Analog Synthesizer. As far as a 'kit' goes, it isn't much to speak of -- just installing the pre-built board* and speaker into the plastic case and wiring up the stylus controller -- but it is such a simple design that it seems built to be hacked on, and that's what I wanted to do.

I did find a number of cool SX-150 hacks, but often they were a bit more advanced than I'm ready for, so I figured I'd start with something simple and slowly build on it and make this a multi-part project. Since I'm really enjoying getting into Arduino programming, an Arduino-based sequencer seemed like a good candidate -- so let's get started with part 1!

It all started when Shawn Augustson of ArduinoFun.com contacted me about including one of my postings in his Arduino project contest. I honestly felt that mine was pretty poor compared to some of the entrants, but it sure was cool to be recognized.

From there it got picked up by MakeZine.com, which was amazing (and that's when my traffic shot up). And from there it looks like I got picked up by Arduer.com which is an Italian-language arduino blog.

Of course, it all seems to be for the 7-segment LED posting, which I think is actually a lot less interesting and technically compelling than the 555 Timer posting, but hey, I'll take it

I'm currently working on a little project involving a do-it-yourself analog synth and the Arduino...let's see if that attracts the same interest.

I was helping a coworker out today, tracking down where all of his drive space went. I knew that Microsoft had a tool for such things -- it's called diruse and can be downloaded here) but I hadn't used it in a long time.

Once installed, it's pretty easy. Open a command window and go to the installation directory (by default it's c:\program files\resource kit), then the command looks something like this:

diruse c:\ /s /d /m /q:1000

This will give a list of all folders that are more than 1000 Mb in size.

To my surprise, I found that there were a number of temporary folders with more than that -- in one case there was a 2 gb temporary folder, filled with (drum roll) Arduino error logs!

They were located deep in a subfolder of a subfolder of my personal files (in my case it was c:\users\jeff\appdata\local\temp), and looked like "console17287.tmp" or "console430.tmp". In each directory there was a stderr.txt & stdout.txt file. These apparently capture the output of the stdout & stderr streams from the Arduino programming environment & language.

In my case, I've had some issues with serial port connectivity and there have been times where I let it sit there spitting out communications errors for a good long while...well, those were buffering up in files, and slowly consuming quite a bit of disk space.

So, if you're doing Arduino development and find yourself wondering "Hey, where did all my disk space go", remember this post. You're welcome.

[Update 12/30/09: I have since found out that the Arduino has hardware timers built in. They seem to be hidden away in the API and I didn't see them when I started, but I will write a little sample with them sometime soon. In the mean time, I think there are still reasons why this is a valid approach in some cases -- plus it's got a simple introduction to interrupt handling, and the 555 timer is still a super useful IC, so hopefully you'll find something useful here.]

Often when I’m programming the Arduino, I can be a bit sloppy about time handling. I’ll throw in a delay(1000) without really thinking about it. And, for the most part, that works just fine. The delay() is just to “slow things down a bit”, and I could just easily have written delay(1111) and not really noticed anything different.

There are times, though, when precision counts.

Say you’re timing something against a video recorded at 30 frames a second – even small inaccuracies can add up and pretty soon your timing is off by several frames. Or perhaps you’re recording data from an experiment and you want to record the results every 1/100 seconds – inaccuracies can skew your results. Or if you're controlling the motion of a device, inaccuracies in timing can cause your expected location to be off.

The key here is an ‘external clock’. Rather than have the Arduino keep track of when to perform the next task, you have an outside signal that says “Now!” and fires an interrupt which the Arduino responds to. If your source fires every 100 milliseconds, then 10 times a second, the Arduino will receive an interrupt which will stop any processing currently happening and immediately execute the interrupt handler. For every tick of the clock, the interrupt handler will execute.

In my case, I was looking to build a synthesizer of sorts and wanted to ensure that I would have a 8000 Hz sample rate, so I had to make sure that the Arduino would do my bidding exactly every 125 microseconds. It turns out I was maybe over-optimistic about the what I could ask of the little guy, 125 milliseconds didn’t leave much time for me to do anything between samples. But I think that if you were in the 1/500th second range, this technique would work very well.