Flash Arduino sketches on the move via Zipit Z2
One thing I've found annoying with Arduinos is the relative lack of options when flashing sketches. A PC is pretty much required. Flashing in the field requires lugging around a laptop. I came up with a solution using the Zipit Z2 instant messenger client. It's a tiny device similar in form and size to one of those newer foldable GameBoy Advance handlelds. It's an interesting platform because of ability (Can run Debian Linux, has built-in WiFi), cost ($30), and battery life (around 5 hours). Unfortunately, it has no external serial port. Fortunately, it's easy to add. Just see this blog post by Geordy Rostad: Adding a Serial Port to the Zipit Z2. I did exactly what he did, except I omitted the level converter, connecting the serial lines directly to the new connector (such a converter would be superfluous when interfacing with an Arduino). Now, my Arduinos are generally at 5V, but the Zipit works with 3.3V. This isn't a problem with data going from the Z2 to the Arduino - 3.3V is plenty to drive the inputs of a 5V device. The other way around requires a voltage divider so we don't harm the Z2. Here's a quick schematic of my converter built into the cable:
» Read full post.SOHA: Main board & test
Etched and populated the main amplifier board last night. Powered it on for the first time and... buzzzzzzzzz. Still sounded rather good with music in it. After a few hours of fussing around, I discovered it was my poor-quality temporary wiring input-side. Strange feedback loops and stuff. I'll be honest, analog circuits are still a dark art to me. Hopefully this project has helped dispel that 🙂 Anyways, now it's using shielded wire and... oh man. Let's just say this thing has broadened my musical horizons. I'll now listen to things on my playlist that I'd usually skip over - it's just such a pleasure to listen to this thing. Still some small noise when the music is stopped. I think that will go away once I finish up the wiring (still a bunch of unshielded sections). Even if it doesn't though, I'll be totally happy!
» Read full post.SOHA: Power supply
The SOHA's power supply is quite simple. It's quite clever how it obtains the ~40 volt B+ for the tube - it basically stacks two full-bridge rectifiers, decoupling them with big caps. To make case layout and circuit debugging easier, I decided to put the power supply on its own board and use various salvaged connectors to hook up to the main amp board. The only mod I made to the original SOHA circuit was use a bigger transformer (1000 mA) to power some eye candy (and put a bigger heatsink on VR3 to handle the extra power). Oh, I also removed the power LED (I've got other plans). I much prefer surface-mount assembly to through-hole (no drilling a thousand little frickin' holes), so I found equivalent SMT parts to the recommended through-hole parts. Here are the part numbers I used for the power supply (refer to figure 4 on the HeadWize page here). Note the connectors are absent from this list - I have no idea what I used. A few years back, some jerk broke our dorm TV. Silver lining: it contained lots of sweet surface mount connectors!
» Read full post.SOHA: PARTS!!
Parts! I love parts. I got a bunch of 'em in the mail for the headphone amp.
» Read full post.Steampunk SOHA tube headphone amp
This is a project that has been floating around in my head for a while. It had fairly innocent beginnings - a few years ago, I bought a nice pair of Audio-Tecnica ATH-M50 headphones. They work great, but I thought adding a headphone amp would make them sound even better. I thought of building the excellent CMoy amp, which the standard DIYer solution to this desire. I decided, however, to use this project to satisfy my curiosity for those charming relics of the past: vacuum tubes. If nothing else, I figured it would make me appreciate today's solid-state devices to a greater degree 🙂 Since I'm an absolute noob when it comes to tubes, I settled on the simple SOHA design by by Alex Cavalli, Mark Lovell, and Bill Pasculle, hailing from HeadWize. It's ideal, since it has a simple power supply, no lethal voltages, and uses only one tube. It's also mildly interesting in that it uses old tubes along with modern high-quality op-amps. That's all well and good, but about the all-important case? You can't have a cool electronics project without a swanky case. Many ideas kicked around: half-plastic-half-wooden case to show the marriage of old and new tech (discarded because I'm not nearly skilled enough in fabrication to pull that off) , a case made from a clear acrylic tube (tube amp! eh? EH?), even an IKEA photo frame. Ultimately though, I realized Steampunk projects are awesome and headed off to an antique store to find a suitable box. $15 later, I had a great box. Guy says it's probably a small-scale sample used by a chest salesman or something. It's pictured below. I haven't finalized the external layout yet, but it's going to involve tubes sticking out the top and the (ab)use of whatever other steampunky bits I have around.
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