It’s not very often that you run across someone who has crafted something unique and cool, but also genuinely useful. Tom Sharpless’s ScanCams fit the bill because they take impressive panoramic images using the guts of old scanners and photographic lenses. Especially interesting is his Mk4 machine. Granted, it may not produce images on the same level as the incredible Gigapan, but it is still an impressive achievement. It’s unclear if Mr. Sharpless has done any work within in the past few months, but we can only hope he will continue development of his awesome cameras.

There are as many techniques for precisely controlling a voltage as there are possible needs for such a technique. Here is a technique I wish I could take credit for, but you may not have seen before. The basic idea is kind of hackish: start with a normal adjustable voltage regulator (can be switching or linear, doesn’t matter) and inject a voltage onto the feedback node. The thing to keep in mind is that a regulator will do whatever it can (ie, raise or lower the output voltage) so that the voltage on the feedback node is always equal to a certain value - usually 1.25 volts. If we inject a voltage onto the feedback node, we can trick the regulator into raising or lowering its output. In reality, the idea isn’t as hackish as it sounds, because regulators are “basically” an op amp (with a high current output) and a voltage reference, which is exactly the key components that most fancy bench top power supplies are based on. The reasons why this technique is so appealing (to me at least):

• Works with any regulator type: switching, linear, buck, boost, inverting, etc.
• If the regulator is capable of it, you can produce negative voltages or a voltage which is above the input voltage by monkeying with the resistor values.
• Can generate an output voltage below Vref (usually 1.25 volts) - you cannot do this with an unmodified regulator!
• Possible to use a DAC or filtered PWM to digitally control the regulator.

Check out the attached Excel file. It will let you mess with resistor values and graph the output voltage. In the file, I have called the voltage we inject on the feedback node Vp. I’ve set up Vp to run from 0 to 5 volts with 10 bit resolution. This is only a brief intro to this idea and doesn’t represent a usable design. Maybe sometime in the future I can churn something out. Enjoy…

digitalreg.xls

I have alot of projects that have most of the design work finished, but need finishing touches and the all important first build. These projects use the venerable ATmega168.

A balanced, bridged two channel amplifier. Idea came from DIYaudio. Actually this still has a fair bit of work left to do.

A super gnarly DAC + headphone amplifier. Has balanced outputs so it can be connected to the amp above. My attempt at “hi-fi.” I got a lot of inspiration and some schematic symbols from a project on DIYaudio.

A tiny robot/experiment board that has USB, 2.4Ghz wireless, dual H-bridges, and most pins brought out to headers. This is going to have to be manufactured at a pretty good board house because of the tight spacings on the CC2500 radio.

An LTC3401 boost converter.

An LTC1871 boost converter.

A “soft start” … this basically switches a power resistor in line with the primary of a transformer for a few milliseconds to limit in-rush current. The whole idea is that this circuit will let you pick a fuse that is appropriately sized for a large transformer since you won’t be having huge transients when the transformer is first plugged in. It’s a dangerous circuit because it works with live mains voltage, so I am kinda nervous about building it. Circuit came from DIYaudio, the layout is the only work I did.

RGB LED controller… after seeing Sylvain Bissonnette’s RGB LED controller, I just had to make my own. My version uses one LM3404 per color and has USB and IR interfaces.

In case you can’t tell, I like to layout PCBs. Keep checking back as I plan to complete these designs and publish ALL of the files.

You don’t have to look very hard to see that web based applications are becoming the new face of computing. While Google probably offers the largest and most comprehensive selection of web based apps, competitors like Zoho, Xdrive, and Facebook have all churned out impressive products that are competing very strongly with Google in their respective areas. That’s where a new site called AppJet comes in. It makes developing web based apps quicker and easier by allowing you to enter Javascript code right into your browser, store it on AppJet’s servers, and access it from a subdomain (myprogram.appjet.com for example). You can also view the source of any app hosted by AppJet. This gives you the ability to learn by example, improve on other’s code, etc. The significance of what AppJet is offering is pretty obvious. The question is, will any Google-crushing applications be built on their platform, or will it just be a collection of millions of useless “hello world” programs? The truth probably lies somewhere in between, but only time will tell for sure.

Virtual Cogs, similar to gumstix that came before them, are tiny ARM based “single board computers” with a family of proprietary add on modules. While not the first on the scene, Virtual Cogs’ front page boldly announces they are “open source hardware done right.” When most people think open source hardware, Arduino or Ethernut immediately come to mind. These two projects freely distribute their schematic and layout files in Eagle format for no charge. Virtual Cogs will provide you with schematics (in an undisclosed format) for a particular part after you have purchased it, but that’s it - no layout files. The concept of open source hardware is much newer than its software counterpart, and perhaps that accounts for the difference in opinions, but I still wonder what VC is thinking.

By now, you might have heard of a company called Zonbu who is marketing a thin client type PC with automatic online data backup and software updates. For an initial outlay of $99, plus $14.95 per month, you get an eBox-4854 with a 4GB compact flash disk running what appears to be a tweaked version of Gentoo. Is this actually a good deal, or not? To exactly duplicate Zonbu’s hardware would set you back about $400 or so. From there, the main problem is that there is very little to choose from in terms of online backup services with a Linux client. The only reputable option I have found seems to be JungleDisk. To match Zonbu’s 50GB of storage space (with 5GB per month of transfer used as an example) will cost you $8.50 per month. At that rate, it will take roughly 47 months before the homebrew alternative to Zonbu becomes less expensive than the real deal. I would say Zonbu has a good thing going. It will be interesting to see if the public embraces Zonbu’s vision of low power, silent computing.

More and more people are experimenting with Kalman filters, gyros, and accelerometers. A fellow named Tom Pycke has been working with Kalman filters for different tasks like autopilots and balancing robots. Tom has gone above and beyond by posting source code, schematics, and board files plus a cool video of his project in action. Bravo Tom!

Pandora may not be for everyone, but I think it’s pretty rad. So rad, in fact, that I have been listening to one station for about a month. This has led me to hear a lot of the same songs over and over again. Almost two years ago, Pandora added the “I’m tired of this song” feature … but either I am slowly going insane, or this feature does not work. Clicking this option will skip to the next song, but as little as six songs later, the old song will be repeated. Someone tell me I’m not crazy!