learning the ropes

Now it’s time to try two of the ultrasonic rangers together and verify that I can use ethernet cable to connect them.  I want to be able to use ethernet cable for several reasons:

• Cheap
• Practically ubiquitous
• Easy to terminate
• Robust

In order to do this, I needed a way to plug an ethernet-style (8-pole 8-conductor) modular jack into a breadboard.  I last built one of these breakout boards when I was working on my thesis at ITP.  It was a time consuming process.

Since I’m planning to use these jacks in this project, it may make sense to create some printed circuit boards.

I’ve written previously about my process for etching boards, so I won’t repeat myself here.  I use a laser printer to put the board design on glossy paper, transfer it to copper-clad board using a hot iron, and then etch away the excess copper using a solution of copper chloride in aqueous hydrochloric acid.

After etching, drilling, and soldering…

The completed prototype circuit works with two sensors. I wrote a patch in Max/MSP to trigger sounds when a person walks past.

We’ve been discussing how to develop the interactive features of the installation.  I ordered some ultrasonic range finders (Devantech SFR-02 from Acroname) to see if they are suitable for our application.

I want to evaluate several things:

• How easy is it to interface several of these devices to a microcontroller?
• Can I use long (30′) ethernet cables to carry the control and data signals?

I hooked the sensor up as shown and found some Arduino code to interface with the sensor and gave it a try.   Success!  So why not try two?

Interfacing a second sensor was a bit more tricky.  The wiring was straightforward: simply wiring the second sensor’s SDA SCL signals in parallel with the existing sensor.  Setting the device address for the second sensor was not straightforward, however.

After reading the manual and trying unsuccessfully to set the device ID, I found a clue in the Arduino examples at Devantech’s website.  The ranger uses 8-bit addresses while the Arduino uses only 7 bits.  This explained why the Devantech documentation listed the default address of the SFR-02 as 0xE0, but the example Arduino code used  address 0×70.

0xE0 (hex) = 1110000

Shifting this number right to obtain 7 bits

0111000 = 0x70 (hex)

One problem solved, but I still can’t get the unit to change its ID.  More Googling turned up an Arduino Library for the SFR-02 by GrapeLabs which includes a ConfigureDeviceID function.

I need some way to understand what types of text “animation” Wendy wants to use before writing lots of code to show her examples.  Bill Buxton describes a number of video techniques in Sketching User Experience.  Perhaps there is a way we can experiment with the animation without doing any coding.

I’m envisioning a space made of foamboard that we can interrogate with a video camera.  We can easily print out text and scroll it in front of the camera to get a sense of what it might look like in the space.

A beautiful projection installation in the chapel on Governor’s Island, by Anthony McCall.

When Wendy and I met, I showed her the sketches and described my desire to better understand how we should animate the typography.  She had already been doing some sketching of her own in Keynote, so we compromised.  We started off projecting some of her slides onto walls.

Then, I quickly built some “gallery walls” using foamboard and we tried bunch of other experiments.  Stay tuned for the results.

Michael’s 3D sketches