Sometimes, the ideal little package comes along and you don’t have to do all the hard work fabricating a physical user interace. While working on the Spot-On project at LKL, I found a very nify little “finger torch” that solves the problem of powering up an LED in a small form factor. This little guy’s is perfect for retrofitting with an LD271 infrared emitter, for Wiimote hacking, IR Motion tracking, and generally mucking about moving around infrared sources, for you Johnny Lee fans. This package combines 3 button cells, a switch and an LED into a tight little case with a hook-and-loop strap. Not sure if it’s emitting continuously or in pulses (PWM) but there’s a microcontroller under that resin blob (pic 2), so it seems likely. A little de/re-soldering and, you’ve got yourself a perfect finger-mounted IR pointer!

People have been asking about the measuring Turtle and I realized I didn’t explain the thing. This is a sort of sensing “LOGO Turtle“, which reads how far the wheels have turned and then uses that data to plot a bar graph. The concept centres around understanding of what a stright line is. Although the notion of “what is straight” seems rather obvious, trying to describe it in geometrical or mathematical terms is a bit tricky. Especially when we move from 2D to 3D worlds. One way of thinking about it is that a straight line is as a path of symmetry.

The “turtle” (okay, it is a turtle with wheels!) demonstrates this in the 2D plane or on a 3D sphere. As long as both wheels are turning at the same rate, the turtle is moving in a straight path, which is symmetrical. By moving the turtle manually across a plane or sphere, the movement of the weels can be observed and compared to to determine straigtness or curvature. This is a way of embodied learning about fundamentals of geometry, which we are using on the Spot-On project. We’re taking the turtle into secondary school classrooms early next week to see what the students think of it. To demonstrate using the turtle on a sphere, we;ve procured a couple of giant (1 metre) sports balls for kids to roll the turtle upon!

The underside of the “turtle” shows the gearing mechanism for transferring the rotations of the independent axles to the sensor wheel. Rather than using an optical encoder - which is basically just too expensive - the sensor wheels pass through the slots of two IR emitter-detector pairs. These TTL logic devices pull up digital pins on the Arduino and this signal is passed to a Processing sketch. The wheels do generate consistent data on the whole, which is what we were aiming for.

The tracking turtle is almost complete. I’ve added the bluetooth arduino board (Arduino BT), though with a bit of trouble getting it to communicate with Processing via firmata. Serial port keeps getting “clogged up”. However, the sensor wheels and IR slot sensor are working as planned.

Resistors for the IR emitter+sensor combo are visible in the undercarriage.