Author Archives: Matthew

Tweet-a-Pot: Twitter Enabled Coffee Pot (now with video)

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This twitter enabled coffee pot has been on Instructables for a few months.  A video, which was added three days ago, really sells the idea.  Of course, most coffee pots already have time-based automatic-start, and nobody that I know has ever used it.  The implementation is very simple.  You only need a coffee pot, an Arduino, and an actuated switch to control AC voltage to the pot.  Will Keurig start marketing machines with a serial port interface in order to compete?

Revamped and Reloaded

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I finally found time to update this blog from Typo to WordPress!  This marks the second migration of this site, and this time I have completely moved away from Ruby on Rails.  Ruby on Rails is still a great tool, but I would not choose it for running a blog on a shared host.  I can’t afford to take a day off every time that the version numbers change.  (Don’t even let me start to complain about the time that my webhost upgraded Rails but Typo didn’t have a compatible version yet.)  WordPress is popular that it has to work, right?  At least I can hope that it will break less.

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 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

Another RCX-based balancer

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I’m a sucker for interesting robots. Especially if they are built out of Legos. Everybody loves the Legway, but you have to admit that the concept is overly simplistic. The real challenge is building the system around the limited resources of Lego’s RCX.

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!

Finally a new layout!

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I officially declare this site back in action! I been ignoring it for too long. Over the past week, I have updated Typo and designed a new layout. This is not the completely final version, though. The header/logo and advertisements need some work. The previous layout performed very well in that department. Hopefully this layout will make up for the difference by attracting more repeat visitors.

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!

Generating Electricity from Sugar

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The headlines for today include research about bacterium that produces electricity by consuming sugar. The Escherichia coli bacteria actually excrete hydrogen after consuming sugar. An electric fuel cell is then powered by the hydrogen.

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.

Are you logical? (Digital logic puzzlers)

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Clive Maxfield recently posed the Black Box Brain Boggler in the Logically Speaking column of May’s EE Times. The original article was incorrect and posed an overly simple problem. In fact, the real problem is much more difficult, but possible none the less.

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.

Capactive Touch Sensing

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My last project brought up the subject of capacitive touch sensing. You may not have realized this, but capacitive touch sensing is currently on the forefront of electronics. Mechanical touch sensors are known to wear and ‘push-less’ sensors are just cooler. In case you did not know, the scroll wheel on an Ipod uses an array of capacitive sensors along with the infamous touch lamp.

Capacitive Touch Sensing

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.

Doorknob touch alarm

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Touch Alarm Breadboard Circuit

I recently found a doorknob touch alarm schematic while browsing Discover Circuits’ archives. The project was originally intended as a present for my brother’s dorm room, but a bad capacitor and the lack of a proper oscilloscope caused delays. It has not made it off the breadboard, and it probably will not until his next semester. The circuit contains a few basic elements, an flip-flop based oscillator, a set of delays, a flip-flop as a sensor, and the audible alarm.

The schematic

Download the schematic

Door Alarm 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.

Oscilliscope without Touch

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.

Oscilloscope with Touch

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.

Oscilloscope Node 9

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.

Alarm Tripped

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

The future of Job Interviewing?

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The Four Dees of Analog is a story written by ADI Fellow Barrie Gilbert about a job interview circa 2025. It is crazy to imagine being interviewed over live HDTV quality teleconference with noncontact stress monitors live at the site. The story goes on to describe the differences between simply collecting information and aquiring knowledge by relating and applying that information.

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.