A bit of history: this blog started out as something that I programmed myself in Ruby on Rails.  I soon realized that Typo had all of the features that I desired with presumably less maintenance.  (WordPress was not quite as far along then.  If I recall correctly, it did not use AJAX back then and most themes relied on tables.  I knew that was not the future.)  I migrated the databases and theme to Typo and Superpositioned.com was born.  It turned out that keeping the Ruby version, Rails version, and Typo version in line was much more than I could handle.  My shared host has moved from CGI to FastCGI to Rails Passenger, which causes even more dependency trouble.  Most of the time that I set aside to create content was spent updating the theme, or some custom code, or playing system admin.  Eventually I gave up on the custom theme, but things still kept breaking every few months.  I have been using WordPress on another site for a year, and it has yet to break (except some obscure `plugins’).  So here we are today after a migration of both the blog and the gallery.  My only complaint is the format of the titles in the current theme, which are not very useful in search engines.

I don’t spend much time on hobby electronics anymore, so I plan to write about other topics as well.  For example: food & beverage, homebrew, and linux/unix.  A reminder of my two most popular posts:

1. Powering LEDs costs mere pennies
2. Doorknob touch alarm

Now meet another balancing robot courtesy of Maurits Kooiman on Lugnet. This one balances on one wheel and apparently uses two RCX bricks and four sensors along with three tires to maintain balance on the axis perpendicular to its unicycle. The robot balances on the main axis by directly powering the wheel. The axis perpendicular to its unicycle is balanced by the set of rotating tires. The fourth tire seems to be a freely swingy pendulum, but it may in fact be controlled by yet another motor. Check out the video!

As you can see, the new layout is significantly better on the eyes. Unfortunately, it has some issues with Internet Explorer 6. Hopefully I can figure out what is causing the extra space to appear. Here is a quick list of the updates:

1. Windows Vista Typefaces: Vista includes some “cute” fonts. If you have them installed, then the new layout uses Calibri. The best way to describe it is “semi-serif.” It actually replaces Times New Roman as the default font in Office 2007.

2. Fluid width and resolution independence. Go ahead, resize your text. The sidebar automatically resizes as well! Of course I also added fluid width. (Fixed width is useless.)

3. The colors are kinder on the eyes. I grew tired of deep red and flashy magenta.

4. Better readability around the ads. I might regret this one, but at least you can read through the copy without getting a headache now.

Watch for a new post detailing my upcoming endevors!

The team fed Escherichia coli bacteria diluted caramel and nougat waste. The bacteria consumed the sugar and produced hydrogen, which they make with the enzyme hydrogenase, and organic acids. The researchers then used this hydrogen to power a fuel cell, which generated enough electricity to drive a small fan.

They are also using the bacteria to recover palladium metal from the spent catalytic converters of older vehicles.

At first, this appears to be deceptively simple. We start with a black box with three inputs–A, B and C–and three outputs (see below). The outputs, which we may name !A, !B and !C, are the logical inversions of the inputs.

The challenge is implementing this black box with only two inverters, a bucket of basic gates, and without a hard coded binary 0 or 1. The bucket of gates presents two levels of difficulty. The former being far easier than the latter. In fact, the first bucket should be easy for any digital design student to solve.

1. The bucket of basic gates contains AND, OR, and XOR gates. Remember, you cannot connect any of the inputs directly to a binary 0 or 1.
2. The bucket contains only AND and OR gates. The solutions are extremely complex, but do exist!

He recently posted the clarifications and some purposed solutions on DesignLine. If you are curious, here are the spoilers for challenge one and two. If you enjoy proofs, there are some more logic puzzlers for your unsatisfied brain.

For the engineer in you, Planet Analog has a lengthy overview. Basically, you design a circuit that is highly dependent on the value of a small capacitor. The capacitance in a finger then causes a significant and detectable change in the circuits output.

The doorknob touch alarm functions in just this manner. It does its job, but is not as precise as more complex circuits. For more schematics, check out Discover Circuits. A recent article on DesignLine proposed that this interface be adapted to mobile phone keypads.

The schematic

Download the schematic

The oscillator

The first section of the circuit is an oscillator based on a flip-flop. Clock and D are both grounded while Reset is tied high. Hence, the output Q will only be high if Set (node 6) is high. When the output is low, the transistor Q1 is cutoff. This allows node 6 to be charged with a delay relating to the system of impedances R1, R2, R3, and C3. Once the voltage at node 6 triggers Set, the output changes to high and Q1 is opened. Node 6 then discharges out through the capacitor. Once node 6 is low enough, Set is no longer triggered and the output is automatically reset (because R is tied high) to low and the process is repeated.

The screen capture below shows node 6 charging and discharging as the blue trace. The yellow trace is the output at node 1. You can see that the output turns high when node 6 reaches the switching threshold of the flip-flop (about 1.8 volts). Right afterwards it spikes up due to feedback through C2, but quickly starts discharging. The oscillator switches off when node 6 returns below the 1.8volt switching voltage. Feedback through C2 draws node 6 to ground before the process repeats itself.

In order to change the period of oscillation, adjust the value at C3. If you would like to make the pulses longer, adjust C2. The circuit works best right where it is at, though.

The delay and ‘sensor’

The output of the oscillator is divided down two paths. The time constants of the two delays are nearly equal and can be adjusted with the sensitivity potentiometer. The path to node 11 is the Clock input of the flip-flop, and the path to node 9 determines if there is an alarm or not.

In the capture above, node 9 high than the the clock. Hence, the flip-flop stays high when the leading clock edge triggers it to lock. When the doorknob is touched, your body absorbs some of the charge and node 9 charges slower. This can be seen in the capture below. When the clock edge rises, node 9 is not high yet and low value is locked into the flip-flop.

The alarm

The designer uses an audible buzzer in order to relay the alarm. This is also my intent for the circuit, but I use a LED in my photos because you cannot see sound. They are both attached to the inverting output of the second op-amp (Q-bar) because it is high when the alarm is triggered.

There is an endless number of uses for this circuit, but I will just name a few crazy ideas:

1. Using the intended buzzer for your hotel or dorm room. (This is a bit more impressive than the old sock trick.)
2. Connecting the output to a relay that triggers the doorbell for you house. Just make sure to put it in parallel with your standard doorbell switch. That way you can still hear the Fed-Ex man. (This one has a major cool factor when someone opens your door.)
3. Tying the output into a security or home automation system. You could have the lights turn on as soon as you touch the door handle to scare the dog away from laying on the door.

Photo Gallery

Of course, this is an article in Analog Devices’ Analog Dialogue so the Sci-Fi aura quickly fades into an advertisement for analog design. In the surrounding of a digital world, the story is a great reminder that analog instrumentation is still all around us. Additionally, it highlights the benefits and challenges of analog circuitry.

What is the difference between a Ph.D. in mathematics and a large pizza?

A large pizza can feed a family of four…

Affordable Programmers

The AVR is well known for how simple it is to program. To start, you only need a few resistors and a parallel port. This will burn your code onto the microchip, but if you plan on pursuing larger projects you will need a more complex programmer with ISP support. This will enable the extra features and debugging support.

1. The ultra low-cost AVR programmer uses an LPT port and a few resistors, but requires special software.
2. A simple serial programmer for Linux uses several resistors and two LEDs. Programming is done with uisp.
3. More complex schematics for ISP programmers that can be programmed via AVR Studio or AVR-Dude.
4. A usb programmer that supports ISP.

A free development environment

AVR Studio is available directly from Atmel at no cost. It has an integrated simulator and programming software. However, there is only an assembler available. You will have to purchase more software for high level languages.

The gcc-toolkit

If you want to use C/C++, then the gcc-toolkit is available for the AVR, free. WinAVR comes loaded with a gcc, binutils, the avrdude programmer, simulavr, and more. On Linux, you will need to download the packages for your specific distribution or compile your own cross-compiler.

A great community

AVR Freaks is a site dedicated to the AVR line of microcontrollers. There is a large archive of tutorials and a very helpful forum.

Once a battery is fully charged, the charging current has to be dissipated somehow. The result is the generation of heat and gasses both of which are bad for batteries. The essence of good charging is to be able to detect when the reconstitution of the active chemicals is complete and to stop the charging process before any damage is done.

Typically, common household batteries are charged with a current that is kept constant and relieved when the batteries reach a predetermined potential. However, solar cells typically generate a constant voltage of 0.5V and a varying current that depends on the amount of collected light. As such, a consant voltage charging model is easier to implement. I found two respectable tutorials on building your own charger:

1. AA Battery Solar Charger
2. Clean Power’s Solar battery project charger

The first solution uses a diode to stop the batteries from discharging when there is no sunlight. I highly reccomend including this protection. Unfortunately, neither project implements a charge limit. You have to remove the batteries and test their charge with a multimeter. A shunt regulator is the simplest way to regulate the upper limit.

After some research I happened to find a deal on a new Instek GDS-820C DSO. The offer was impossible to refuse and cheaper than the GDS-805C. Besides the obvious increase in sample rate, the GDS-820C comes standard with USB and parallel ports along with the RS-232 port, but GBIP is still only an option. These digital storage options will allow me to post pretty pictures on the blog!

This oscilloscope samples at 100MSamp/sec and is capable of 150mHz operation. They claim an ‘effective’ sampling rate of 25GSamp/sec when viewing repetitive signals. In comparison, Tektronix base model samples at rates up to 1GSamp/sec.

At 150mHz it will be hard to see much if the signals are not repetitive! If you know anything about Shannon’s Sampling Theorem, the effective sampling rate makes 150mHz operation seem… possible. Without this hack, the scope would be limited to half the sampling frequency or 50mHz. I could have paid more for a Tektronix scope, but the hardware would have been limited to 40mHz, mono anyway. This will suit my needs.

Update: If you view a signal sampled at over 100MSamp/sec, then you can tell it is making due with the effective sampling rate. I am not sure if this really matters because I do not have access to signal over a MHz at the moment.

PC Magazine has a review along with the infamous Myth Busters. Their main gripes were a lack of accessories and motors that were geared for speed instead of power. Combined with the weight of a steel frame, this hindered a their stair climbing application.

A rich system of hardware, software, and powerful sensors, along with documentation that doesn’t skimp, makes this a terrific first experience with robotics for anyone. Well-machined. Expertly documented. Quite powerful. Tremendous fun. – From PC Magazine’s Review

Compared to other robotics kits in its class, the Vex system is capable of creating some rather large robots.

The good news is that the site is back up and running. Dreamhost has also rolled back to Rails 1.0 allowing Superpositioned to speed along on FastCGI again.

Unfortunately between this fiasco and a borked Typo upgrade earlier this week, I have exhausted what little spare time I had. I promise updates soon, though. My TODO list is full of circuits and projects!

Update: As of April 4, 2006 everything should be working again. Wait.. I am getting the “Typo failed to start properly” message randomly again.

Update: A few minutes later and you should no longer be receiving that message.