Archives for the month of: October, 2012

This Thursday, half of our class conducted a focus group at the apartment building we’ll be using for our sensitive buildings class.  The building is located right on Columbus Circle, with one side of the building facing Central Park.

Our focus group had three attendees, one couple (Lynn and Ralph) and one single woman (Gabby).

Lynn and Ralph had been living in the building for a year and a half, having moved into the building after Lynn’s mom, who also lived in the building, passed away.  They were accustomed to being friendly to the people in the building and enjoyed the atmosphere and area.  Ralph, an attorney, walks to his office in Times Square and always wakes up before 6 am.  Lynn works as a college professor and likes to exercise in the park every day.  She says that “getting to the park is a must”.  Occasionally they might use the apartment’s in-house gym if the weather is really bad.  They have children that are older, but live close by.

Gabby has lived in the building for 8 years (in the smaller tower), and was blonde, tan, and smartly dressed.  She also had a German accent, though I couldn’t pinpoint it as German at first.  She works for the UN three days a week, walks to work, and has an Italian husband.  She’s lived all over the world, but explained that New York was definitely her favorite place to live.  She seemed to have a strong need for a homey, cozy environment.  She loves curling up by a fireplace, drinking a glass of wine, or maybe laying on the apartment balcony, soaking up a bit of sun.  She said it herself, “home is everything”.  She explained that her home is her “little slice of heaven” and seemed perfectly content to live in the “little village” (as she calls the smaller apartment tower) indefinitely.  Gabby mentioned that she occasionally hears horse hooves in the morning (coming from Columbus Circle).  It makes her feel as if she’s been “transported in time”.

What I found most surprising is just how content these tenants seemed and how much they loved the apartment and the area around it.  Towards the end of our conversation, they started discussing  seeing the building in other contexts and their pride was evident.  Both Lynn and Ralph and Gabby had photos of the building.  Lynn and Ralph had their’s framed, while Gabby received photos of NY for a 30th birthday, back when she was living elsewhere.  They excitedly mentioned the places that you could see the apartment – on TV during the Macy’s parade, in “Miracle on 34th Street”.  They even said that Antoine de Saint-Exupéry, the author of “Le Petit Prince”, used to live in the same building!

I’m unsure of what I’d like to do for the final project, but the focus group definitely gives me some food for thought!  It should be something that is worthy of the building and perhaps something that enhances the spaces Lynn, Ralph, and Gabby feel so strongly about.  As a side note, they did mention that they loved the last installation and were open to more artistic pieces!


This week, I made my first marionette!  I went to Compleat Sculptor in search of wood and carving tools…I was clearly feeling optimistic – I walked out with just a solid block of basswood and a hand chisel.  The last time I carved something (whittling a stick in the woods), a pocket knife closed on my finger, leaving most of my finger’s meat hanging on by only a bit of skin.  I still have a prominent v-shaped scar to remind me NEVER TO WHITTLE STICKS.

I started off carving by cutting the block into what I thought where manageable-sized chunks (note to self: they were huge).  I started by chiseling away at the blocks while watching the Princess Bride on my bed.  I chiseled into my hand twice.  Mistake.

From there I moved onto the belt sander.  This time, I had more success!  I found it was fairly easy to make leg and arm pieces!  After getting a decent shaped, I also tried to use the dremel to carve out some details.  I wasn’t great at this, and my puppet only barely has a nose.  I attached my joint pieces with eye screws and a bit of felt.

Next came the painting and stringing.  At first I toyed with the idea of making a marionette avatar of myself, but then it went in a weird direction…I ended up painting meat on the insides of my joints…

Here’s the marionette after painting and stringing.

Hanging from the ceiling…

If I have more time, I think I’m going to modify a few joints and add more strings.  The marionette is somewhat floppy to control!


This guide will show you how to design an LED ring oscillator circuit of any size.  You can use LED ring oscillators to produce cool, glowing effects without using a microcontroller.


Conceptually, a ring oscillator is a circuit composed of an odd number of “inverter” gates (or NOT gates).  An inverter takes an input (either HIGH or LOW) and outputs the opposite value.  If we hook up an odd number of  inverters in a ring, one inverter will cause the value of the next inverter to switch.  For example, if we supply one inverter gate with a ‘HIGH’ value, it will in turn supply the next gate with a LOW value, which will supply the third gate with a ‘HIGH’ value.  The last inverter will then output LOW (the opposite of HIGH).  In a ring oscillator, the output of the last inverter is then connected to the input of the first inverter.  Now instead of being supplied with a HIGH value, our first inverter is supplied with a LOW value, reversing its output.    With an odd number of inverters, each pass around the ring will reverse the value of each gate.  Thus, the gates will constantly “flip” their values (or oscillate) in this unstable circuit.

If you use an even number of oscillators, the gates do NOT continue to flip – the circuit will stabilize.

If we add some LEDs, resistors and capacitors, we can control how fast each it takes for each gate to flip, controlling how long an LED lights up.  In this case, we’ll be using the discharge of a capacitor to flip our switches.  If we use very large capacitors and resistors, each LED in the ring oscillator will stay on for a longer amount of time.

Here is an example of a three-ring oscillator that moves fairly slowly:

Here’s a faster ring oscillator with more gates:



For an N-ring oscillator, you’ll need the following:

N MOSFETs (I used part number IRL510, purchased from Mouser)
N ceramic capacitors of value x
N LEDs of whatever color you wish
N resistors of value y
N resistors of value z,
A power supply, such as a 9 volt battery

A breadboard, wires, and wire strippers are helpful for prototyping the circuit

First things first – you’ll need to figure out what values of resistors and capacitors you’ll need for your circuit.

Step 1: Calculate LED resistor value

Since you’ll be powering LEDs in your circuit, you’ll want a current-limiting resistor.  I usually guesstimate the resistor value, but you can also use this handy online resistor calculator.  You will want to know the forward voltage drop and the forward current for your LEDs.  LEDs usually have a forward current draw of around 20 mA (30 for super bright LEDs) and a voltage drop of 2-3 volts depending on the color (check here for a rough estimate of LED voltage drops).

The LED resistor is denoted as “LED R” in the hand-drawn schematic.

Step 2: Calculate RC Circuit Resistor and Capacitor Values

When designing a ring oscillator circuit, you must decide how fast you want the LEDs to turn on.  The length of time that each LED is on is determined by the amount of time it will take for a capacitor in one leg of the circuit to charge up.  We determine this value by using the following equation to solve for time:

T = R x C, where T is measured in seconds, R is measured in Ohms and C is measured in Farads

For instance, if I wanted each LED to be on for about 1 second, I could plug in:

1 s = R x C

Experimenting with the R and C values, I might decide to use a .1 microFarad capacitor and a 10 MegaOhm resistor, or a 100 k resistor and a 10 microFarad capacitor.  Again, there is handy online tool available.

Alternately, instead of calculating resistor/capacitor values based on how long each LED is on, we can calculate the values based on how long we want it to take for our ring oscillator to flip all switches in the ring one time.  To calculate in this way,

Total time for all gates to flip = N (number of rings) x R x C

If I had a 7-ring oscillator and wanted it to flip all LEDs in one second, we’d use:

1 s = 7 x R x C

0.14 s = R x C

and use the same online calculator as before to experiment with values.

Step 3: Understand the Circuit and Build!

Here is a circuit diagram for a 3-ring oscillator circuit.  You’ll notice that it’s essentially the same circuit (an LED, two resistors, one capacitor, and a MOSFET) repeated three times.  Then, we connect one side of the last capacitor in the ring to the first MOSFET in the circuit.  You could have an arbitrary (odd) number of segments in your ring as long as you make this connection from the last piece of your ring oscillator to the first piece.

If you’re not accustomed to reading circuit diagrams, it’s important to know how to connect each piece of your circuit.  The resistors and ceramic capacitors are not polarized – it doesn’t matter which direction you put them in the circuit.  The LED and MOSFET must be connected in a certain way.  For the LED, make sure the long lead is connected to VCC.  For the MOSFET, refer to the schematic diagram and drawing below.

Step 5: Admire Your Work and Notice Cool Things

Hopefully you’ve been able to follow this guide and design your own ring oscillator circuit.  Now, it’s fun to notice something strange about your ring oscillator.  Every time you plug in your circuit, it will start lighting up from a different location.  This is because we never explicitly flip any of the switches.  Electricity flows in to the circuit, charging multiple capacitors at once.  Whichever capacitor (randomly) fills up first will start the oscillation!  Try it!

For my birthday last year, my boyfriend made me a really cool necklace with an even cooler circuit (see this link for the circuit he based his present on).  He used a ring oscillator to make LEDs glow in a beautiful pattern using only analog circuits!

I wanted to make a ring oscillator for myself, so I thought this would be a great time to test it out.  I wanted to make a paper, jellyfish-inspired paper circuit, with a few slowly glowing LEDs to add a nice effect.  I made a paper tilt sensor with conductive paint, conductive thread, and a brad to turn on the circuit.  Here are the results:

For my Puppets class, I made an (o)possum hand puppet out of foam, fabric fur, and some felt.  Why a possum?  Possums are amazing…and scary.  I first remember seeing a possum in my backyard in Luther, Oklahoma.  It was hissing until my dad tossed it over the fence with a shovel.

Possums are the only marsupial in the United States, plus they involuntarily lose consciousness when scared (and emit stinky fluid).  They can be out cold for up to four hours!  This, of course, is the inspiration for the term “playing possum”.  Baby possums occasionally “play possum” at the wrong times.  Can you imagine a baby possum passing out for no reason?

To make my very own possum, I hot glued together several pieces of thick foam (harvested from Ithai’s office) and started carving a possum shape.  At first I relied mostly on scissors…this eventually gave me horrible hand cramps so I used a saw to cut off larger chunks.

After achieving a shape I was happy with, I cut out a tunnel (starting at the back of the head) that I could fit my hand into.  I hoped to control the possum puppet’s mouth with my hand, so I also hollowed out part of the snout and lower jaw.  Everyone thought my possum was a duck so I glued a bit more foam to the nose to make it pointier.

I then glued fur fabric to my possum’s face and sewed a shape for the body.  Unfortunately, the fur was adhesive-backed, making it very difficult to work with.  It kept sticking to itself and I would have to pry it apart.  I made possum ears and a nose out of felt.  I was especially pleased with the nose.

I picked up some plastic eyes at Blick and used more left for the face, teeth, and inside of the mouth.  As a last step, I sewed on some little feet, stuffed the body with foam, and made a tail out of felt.

I didn’t get to finish Olive’s feet, but I’d like to add some pink claws at some point!

For the second part of our assignment, we had to make a documentary about our puppet.  Since I was about to leave town for a wedding, I decided to incorporate the wedding location into Olive’s backstory.  The wedding was held at Robber’s Cave in Wilburton, Oklahoma in the Ozark Mountains.  When I showed him my possum puppet, my friend Mehan told me about the story of possums in Brooklyn.  Apparently, Brooklyn possums are out of control.  In the 90’s, someone thought it would be a good idea to release wild possums in Coney Island, hoping they might eat a few rats.  Unfortunately, possums don’t eat rats.  They do eat trash, however, and the Coney Island board walk was a veritable smorgasbord.  Now there are even possums riding the D train.  I started wondering where they (whoever “they” is) sourced the possums for the Coney Island project, which served as the inspiration for Olive’s story.

Olive was born a country possum, out in the Ozark Mountains.  One day, she was snatched as part of the Great Possum Roundup.  She was relocated to Brooklyn, NY and never saw her family again.  My documentary explores Olive’s return to the Ozarks and her readjustment to country life.  I’m not completely happy with the movie at this point, but will post when I have made more edits.  Hint: it features a possum on a plane.

In preparation for using XBees in my Sensitive Buildings class, Yin and I did a few tests.  First, we configured the XBees using X-CTU on my laptop and made sure they were communicating using a terminal program.

In this example, one Arduino is detecting a button press.  When the button has been pressed, it sends a wireless message through its XBee.  The other XBee receives the message and tells the other Arduino to play a song.  We later modified the example so that the first Arduino would light up an LED to confirm the song had been played. Here are our results!


I used XBees pretty extensively for my thesis at Wellesley, and I’m really excited to use them again!  This example uses Arduinos and XBees to send a simple button press, but this can also be accomplished using only XBees (“XBee Direct”).  This week, I hope to use XBee Direct to make a pair of interactive paper circuits.