Graffiti is one of the most powerful and most personal displays in the urban experience, and can be used to make statements, tag territory, spread messages - urban markup language in practice. However, the output is nearly always visual in nature, making this experience one-dimensional. Furthermore, rarely does the work have a brain of its own, and is usually incapable of reacting to anybody observing it. Concrete Crickets was created to address this deficit, creating small devices that will be aware of passers-by as well as other units of their kind. Each unit consists of a sound generator, amp, speaker and sensory system, and is housed in camouflage appropriate to the streets of the city - soda cans, cigarette packs, and the like.

I love the streets of NYC (and just about any other city), but it seems to me that the "magic" moments of serendipity are harder to come by. If this project can just create one moment of magic and beauty (corny as both those terms can be), than it will have succeeded with flying colors. Inspired by field crickets and fireflies on one hand and street artists on the other, this project aims to create, by installing small "crickets" in a small area of city space, a multi-directional audio experience. Each device is programmed with a particular voice, with each bieng part of a larger whole. When night falls, the crickets go active for a few hours, singing out in their particular way. When approached, the crickets fall silent (as would crickets and cicadas in nature). Each are sensitive to what happens to the others, and the end result will be waves of songs, changing and adapting to their surroundings.

Each unit contained an Atmega8 chip running Arduino, an OpAmp circuit, an ultrasonic rangefinder, two relays, a few capacitors to smooth out readings and values, a 1" flat speaker, an itty bitty speaker (which I dont't think I'll bother using in future versions), a hacked MP3 player, a AA battery for the MP3 player, a 9V batery to power the rest of the circuit, and a few other odds and ends. This was all soldered onto a perfboard which was then wrapped in a plastic bag and shoved into a crumpled soda can.

For more info visit Mike's ITP Projects and participate in the Concrete Crickets discussion forum at Octopart News.

working on cool hardware? submit blogs to contact@octopart.com

Today we are releasing a new feature that, I hope, will make searching for parts a lot easier and a lot more fun: Octopart News.

Octopart News is an experiment that we are very excited about. We envision it as an open forums site where you can post technical questions and hopefully answer some too. You can also post links to interesting engineering/tech news stories. For instance, the discusion thread to Sam's last blog is here and the first mention of the word "Semiconductor" in the NY Times can be found here.

One of the great things about places like Reddit and Paul Graham's Startup News is that you can find interesting stories everytime you visit. We wanted to build a place for engineers, researchers and hobbyists to go and find find interesting tech stories all in one place. Selfishly, this is going to be our way of keeping up to date with cool new hardware projects. Hopefully you'll find the same is true for you.

When we were building a laser for our experiment at the South Pole we needed a communications device that operated at -50 C over 2.5 km of cable. It took us 3 weeks to find what we were looking for. Now, you can submit a discussion topic to Octopart News and somebody who has had the same problem can tell you what their soution was (an ethernet extender). For our part, we will be adding tools to make this process easier.

Tell everybody you know about Octopart News and help us build a useful and fun site that will make it easier for you to keep building things.

working on cool hardware? submit blogs to contact@octopart.com

If you want one of the PCBs, email me with your mailing address and I'll drop one in the mail to you at no charge Sorry, they're all spoken for.

I also had a chance to clean up the circuit diagram. You can download the schematic in pdf or flash format. The schematic is broken down into two parts, the power section and the amplifier section, as shown below in miniature.

The doublet uses a 9V battery along with two TLE2426 railsplitters to generate a virtual ground and supply rails at +/-4.5V. For power savings, only one side of the power supply and one of the op-amps is active if a single channel is on. A 11DQ03 diode keeps things from breaking if you accidentally put the battery in backwards. This diode has an extra-low forward voltage drop of 0.55V which is nice for battery based amplifier circuits. The dual power supply is based on Tangent's TLE2426 virtual ground design.

The amplifier stage starts at the input jack. The left and right audio channels are each split in two and fed into the volume potentiometers. Capacitors C3, C4, C5 and C6 act to protect the op-amp from any DC offset at the inputs. The op-amps are configured in a textbook non-inverting configuration with 14dB of gain. The amplifier circuit is based on Chu Moy's original Cmoy design.

Here is one set of parts to fill the board:

• Capacitors
• Signal capacitors 4x EPCOS B32529C5334J(0.33uF)
• Power supply capacitors: 4x Vishay 2222 150 65471(470uF)
• Resistors
• 4x Vishay RN55D1001F(1kΩ)
• 4x Vishay RN55D4021F(4kΩ)
• 2x Vishay RN55D1002F(10kΩ)
• 4x Vishay RN55D1003F(100kΩ)
• Railsplitters: 2x Texas Instruments TLE2426
• Diode: 1x International Rectifier 11DQ03
• Audio Jacks 3x Switchcraft 35RAPC4BH3
• Op-Amp Sockets 2x Areva DIP308-001BLF
• Op-Amps 2x Texas Instruments OPA2134PA
• Potentiometers 2x ALPS RK0971221Z05
• Knobs 2x Multicomp MC0616003
• Indicator LEDs 2x Avago HLMP-K150
• Battery Strap 1x SPC 8459-0674

Keep in mind that the parts I've listed here are only suggestions. Though I've listed nice precision resistors for the audiophiles in the crowd, if you have some through hole resistors already, they will work fine (especially the LED resistors which don't need high precision).

There are many nice audio op-amps which will work in this design. In fact, the doublet amplifier can serve as a nice test bed for head to head op-amp listening comparisons.

Finding the ALPS RK0971221Z05 potentiometer in small quantities at a good price can be tricky. Tangent sells them in single pieces for $3.25 each which is reasonable.

Please send feedback on the circuit and the board layout as there is definitely room for improvement in both. The original Eagle files can be downloaded for those of you who are interested in moving the design forward. A few ideas are:

• Miniaturizing the board with SMD components.
• Adapting the power supply design to run off of AA, AAA or some lithium polymer battery.
• Adding a trickle charger for use with rechargeable batteries.
• Clean up the Eagle schematic (not the one shown) with better drawings for the potentiometers.

Assembling the doublet into an Altoids tin will have to wait for another post. Just remember to insulate the bottom of the PCB from the Altoids tin!