Timothy Ireland, Gage Tiber, Robert W.A. Brooke, Julie M. Gillis, Christopher A. Zaccagnini, Theodore A. Corcovilos
Dept. of Physics, Duquesne University, Pittsburgh, PA; Pittsburgh Quantum Institute (http://www.pqi.org)
TEMPERATURE CONTROLLER
Design
54.85
56.5
Future Work
0.1
B)
54.8
56
54.75
54.65
0
55
50
100
20,000
Time (s)
0.01

54.7
55.5
54.5
0
 ( C)
output of a temperature sensor to the
Arduino, which uses digital PID feedback to
control heater output through Pulse Width
Modulation (PWM). This gives consistent
temperature stability of 7 millidegrees.
The second instrument is an automated
wavelength meter for picometer resolution
measurement of visible and infrared lasers.
The
optics
include
a
Michelson
Interferometer containing two parallel
beams: an unknown and a Helium-Neon
reference beam. This requires a counting
circuit and motor driver circuit, both of
which are controlled by the Arduino. The
Arduino also
monitors temperature,
pressure, and humidity sensors for on board
calculations of the index of refraction of air
using known equations (Ref. 1). In addition it
controls an interactive LCD display for
inputting preset information and displaying
statistics.
250 500 750 1,000
40,000
0.001
60,000
1
10
Integral gain
(c)
1/512 1/128 1/64
Proportional
gain
Arduino is an open-source micro-controller
platform designed for quick development
and easy interfacing, making it ideal for
novice
programmers
and
instrument
designers. Based on Atmel ATMEGA
microcontroller chips, the Arduino boards
are programmed with standard C/C++ code.
The Arduinos have six 10-bit analog (ADC)
inputs, fourteen digital I/O, pulse width
modulated outputs, as well as hardware for
SPI and I2C serial communication and USB
encoding hardware. We have chosen to use
the Arduino because it streamlines data
acquisition and processing when compared
to circuits using discrete components and has
robust enough software to run complex
algorithms and control routines on the
microprocessors themselves.
The first device we describe is a
temperature controller used to heat a
potassium vapor cell. This circuit reads the
(b)
(a) 57
Temp. ( C)
INTRODUCTION
Characterization Data
1/16
1,000 10,000
1/8
1/8 0.025 0.021 0.019 0.02 0.02
1/4 0.013 0.012 0.007
1/2
100
 (s)
Stable
Oscillating
0.23
The wave-meter circuit will
be constructed using surfacemount components to save
space and to reduce noise. The
interferometer optical and
mechanical system is under
construction and will need to
be
finished
before
full
evaluation of the effectiveness
of the wave-meter setup is
complete. The Helium Neon
reference
laser
will
be
stabilized using polarization
based temperature feedback,
as the effectiveness of this
design depends on an accurate
known wavelength reference
beam.
Best
Optical layout of the wave-meter
Figure 2 – Temperature controller characterization. (a) Sample data set showing the
initial settling of the temperature and the long-term behavior (note the change in the
horizontal scale). The inset is a zoom near the end of the data run. (b) Allan deviation of
the temperature as a function of averaging time. (c) Parameter matrix for the PID
controller setting. The standard deviation of temperature (°C) over 1000s is shown.
Circuit Block Diagram
Future Work
We will use the temperature controller circuit to heat a potassium vapor cell for saturated
absorption spectroscopy. The circuit and software will be made publicly available soon.
WAVELENGTH METER
Design
We designed a picometer-resolution wavelength
measurement apparatus for lasers in the visible range. A
digital counter circuit interfaces with a Michelson
interferometer. Initial concepts were derived from Ref.2
𝑁
using the relationship 𝜆𝑈 = 𝑅 𝜆𝑅. .Where 𝜆𝑈 and 𝜆𝑅 are
𝑁𝑈
Figure 1 – Simplified schematic of the temperature controller circuit.
We present a temperature control (Fig. 1) circuit driven by an Arduino microcontroller. The
bridge and instrumentation amplifier map a temperature range of 0 to 80oC, as read by a
PT100 platinum resistance thermometer, to a voltage range of 0 V to 5 V.
Since all components are driven by the same Vref = 5 V, the signal is insensitive to supply
fluctuation. Precision, low temperature coefficient components are used for stability and
repeatability. Oversampling of the 10-bit analog-to-digital converter (ADC) in the Arduino
allows us to use an effective 14 bits, resulting in a temperature resolution of 6 mK. We
modified a PID feedback algorithm (Ref. 3,4) to use integer math for faster calculation,
resulting in a speed-up of 30%. The output is a PWM digital signal modulated at 1 kHz, which
switches a high-side p-channel MOSFET to drives a 15 W resistive heater.
The circuit consists of two parallel channels, reading two sensors and outputting to two
heaters.
We optimized the stability of the temperature by varying only the proportional and integral
gain parameters (P and I), as shown in Fig. 2. Our best parameters are P = 1/4, I =1/64, D = 0
for a sampling rate of 0.6s (Fig. 2c). At those settings we measured mean T = 55.073 °C
(compared to our setpoint of 55.0 °C, with a standard deviation = 0.007 °C. The settling time of
the circuit is about 120 s (Fig. 2a). To characterize the long-term behavior, we measured the
Allan deviation for a 17 hour data run (Fig. 2b). The highest stability is ±0.002 °C over ~100s
measurement times.
the wavelengths of the unknown and reference laser,
respectively. 𝑁𝑈 is the number that will be counted down
by the fringes unknown laser and 𝑁𝑅 is the number that
will be counted up by the fringes of the reference laser.
By setting 𝑁𝑈 to be the numerical value of the reference
wavelength in picometers, 𝑁𝑅 will be the wavelength of
the unknown laser in pm. The counting is done with
parallel sets of counters recording counts from
photodiodes. We modified this design to take advantage
of an Arduino, in order to simplify the circuit and the
collection of data. Additionally, the Arduino reads
atmospheric
pressure,
relative
humidity
and
temperature sensors to correct the measurement for the
index of refraction of air.
Characterization
Testing indicates that the wave-meter counting circuit
operates more quickly than the anticipated fringe rates
for the measurement of visible or near infrared lasers.
When fed with a digital signal generator, the circuit
operates entirely without error over a large number of
trials (n>100) with input frequencies of up to 2MHz, a full
order of magnitude above the highest frequency output
that could be expected from the Michelson wave-meter
design.
CONCLUSIONS
Arduino is a useful and versatile laboratory tool, facilitated by its support of generalpurpose programming, diverse electronic communications interfaces, and powerful enough
processing for precise lab equipment.
REFERENCES
1.
2.
3.
4.
P. Ciddor, Applied Optics 35.9,1566-1573 (1996). doi: 10.1364/AO.35.001566
P. J. Fox et al. Am. J. Phys., 67.7, 624-630 (1999). doi: 10.1119/1.19335
B. Beauregard http://playground.arduino.cc/Code/PIDLibrary (retrieved 6/4/2015).
B. Beauregard http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pidintroduction/ (retrieved 6/4/2015).
ACKNOWLEDGEMENTS
We thank Duquesne University for financial and material support, particularly the Bayer
School of Natural and Environmental Sciences, the Office of the Provost, the Undergraduate
Research Program, and the Faculty Development Fund. Technical help was provided by the
Bayer School instrumentation shop.
CONTACT INFORMATION
Ted Corcovilos, Department of Physics, Duquesne University, 600 Forbes Ave. 317 Fisher Hall,
Pittsburgh, PA 15282. Email: corcovilost@duq.edu Ph: (412) 396-5973