Digital Designs and Scientific Hardware - Open-Source Lab: How to Build Your Own Hardware and Reduce Research Costs - page 180

FIGURE 6.17 Open-source lab jack.
3-D printing and the Arduino can be combined to create automated dynamic optics systems
such as the open-source parametric filter wheel 28 shown in Figure 6.18 . This version of the
device has a printable wheel with eight filter slots equally spaced by 45°, an Arduino Uno mi-
crocontroller, a stepper motor, a discrete optical switch flag, a sensor composed of an output,
two ends and a light beam that goes from an end to the other. When the light beam is blocked,
the output signal changes depending on the logic used (e.g. from high to low). Through a
computer interface, the user can set the wheel position to the desired filter by clicking on the
buttons displayed on the screen, also an indicator provides the current position of the filter
wheel. The user's input is read by the Arduino's serial communication port, the optical switch
flag denotes the filter wheel's origin (e.g. assuming the filters are indexed from 0 to 7, the filter
0 is detected when it passes through the sensor). Each time the device is turned on or restar-
ted, it rotates until it finds the origin. Using the current location of the filter stored inside the
memory and the optical switch flag information as feedback, the Arduino interprets the input
and drives the stepper motor following the logic created by the program code until the de-
sired filter is positioned and the input matches the output. The logic always uses the shorter
path until the next filter by calculating the difference between the next and the current filter
and always passes through the origin when it is possible to maintain calibration. This auto-
mated filter wheel, which only costs about $50 to make, saved my laboratory from spending
$2500 + shipping. It was exactly what my lab needed and having made the initial investment
in the design, we will never need to purchase one again.