Open Source Physics Laboratory Data Acquisition System V 2.0
Dr. John Liu
Department of Chemistry and Physics, Saint Cloud State University, St. Cloud, MN
AAPT annual meeting July 2013
Introduction
Open source physics laboratory data acquisition system V 2.0 (OSPL
V2) is a physics laboratory data acquisition electronics platform
supplement/alternative to commercial platforms such as PASCO
Probeware or Vernier LabQUEST. You can build a unit yourself that
costs as little as $30. OSPL V2 is an update from the OSPL V1 that
won AAPT apparatus competition in 2012. It can be used with
sensors/actuators to perform experiments, process data, and even
make your own creative projects. It is portable for activities
outside physics lab rooms. Both circuit board and firmware/code
are open source.
Objectives
• Improve experimental physics education at introductory level
• Improve hands-on skills of physics instructors and students
• Build a platform and community to promote teaching and
learning experimental physics using cost-effective electronics
• Build a community to support constructing, using, and improving
OSPL system and software design
• Reduce the cost of and time to build an OSPL unit so it is
accessible to anyone interested in experimental physics
Analog input accuracy
Pictures
(A) Circuit board
(unpopulated)
(B) Assembled kit
(C) Assembled kit
in enclosure
(E) Schematic
diagram
(F) Circuit
board design
The accuracy of analog input is 5mV. We used a Vernier dual-range
force sensor at 10N range to test our system. Masses were loaded to
the force sensor in 20 gram increments and force reading was taken
from the system. The horizontal axis is the weight of the mass on
the force sensor. The vertical axis is the force read from our
system. We found a very good agreement between the two with
scaling parameters provided in Vernier’s manual.
10cm
(D) Displaying temperature,
force, and pressure
System specification
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Microcontroller: ATMEGA328P-PU compatible with Arduino Uno
Program memory: 32KB, rough max 3,000 lines of C/C++ code.
Variable memory: 2KB, roughly stores up to 1,000 data points.
EEPROM: 1KB, roughly stores up to 500 data points.
Supports up to 3 autoID analog sensors (Vernier resistor-based) or
up to 6 analog sensors without autoID
Supports up to 8 digital inputs or outputs for photo gates,
counters and sonic rangers.
Support I2C sensors that are widely available at very low cost
On-board 16X2 character LCD monitor with back light
On-board speaker for simple tones
LCD back light jumper to disable back light to preserve battery
Wireless and wired data transmission with a PC/Linux/Mac
Rotary encoder for easy menu navigation (up/down/select)
Elegant enclosure ready to use
Massive amount of library and sample codes as templates to start
a project or load pre-written code for specific tasks.
Compatible sensors
Vernier sensors
• All analog sensors with a linear voltage to measurement relation
are compatible, such as force sensor, temperature probe, voltage
probe, pressure sensor, accelerometers, barometer etc.
• BTA-DIN adapter is needed for BTA interface analog sensors ($5)
• Most digital sensors such as sonic ranger, photogate, rotation
sensor, drop counter etc.
Digital input accuracy
Benefit of open source hardware and software
Hardware freedom
• You only pay parts and board production ($30) and spend time
• You may modify the circuit in any way that suits your own needs.
• Circuit board is very easy to solder even by kids, 1-2 hours, no
prior experience needed
• Freedom to choose from many sensors that cost only small
fractions of those sold to the educational market.
• Design the coolest physics projects with the freedom of OSPL
Software freedom
• Included firmware works with a large number of sensors
• Software development environment is open source
• To program the unit yourself, 4-5 lines of code is enough!
• More sample code for more complex tasks free to download
• Compatible with Arduino that has the biggest online DIY
community and resources for beginners from any background
Plans
Projects and activities with OSPL
• Included firmware can be used in labs to display up to 3 sensors
on LCD, or transfers readings to PC/tablet via wireless or wired
connection. See fig. C and D.
• Make a simple data logger with as few as 4-5 lines of code
• Make a weather station with compatible sensors
Project highlights
Code to sense and display an input
reading=analogRead(channel); Line 1: acquire data
result=a*reading+b;
Line 2: scale data for output
lcd.clear();
Line 3: clear LCD
lcd.print(result);
Line 4: output result
delay(200);
Line 5: pause for user
• Explore more Vernier analog and digital sensors, due to their
simplicity to integrate with OSPL.
• Expand to more modern sensors.
• Write enough sample codes to kick start projects.
• Design sample projects for instructors and students to try out.
• Build a website to host the content
• Branch out a “headless” system (no display or buttons but
wirelessly connects to mobile devices) for even lower cost and
improve current design with feedbacks.
Conclusions and future directions
Pasco sensors
• Pasco photogates, strobe light, sonic ranger etc.
High quality low cost sensors
• I2C interface sensors: accelerometer, barometer, magnetic
sensor, gyroscope. One such board that includes all of above
costs $13 on ebay.
• Lots of analog and digital sensors can be used. The user just
needs to develop as few as 4-5 lines of code and do the wiring.
• OSPL has a 16MHz clock and can easily achieve 10us accuracy.
• With special programming one can achieve 1/4us accuracy.
• The above accuracy applies to photogates, sonic rangers, rotary
sensors, and other simple digital on/off and pulse width sensors.
• Modern I2C interface sensors digitize measurements themselves
so OSPL receives measurement at maximal sensor accuracy.
• With I2C analog-to-digital converter, OSPL can go beyond 5mV
analog accuracy, for as little as a few dollars of parts.
• TTL serial port sensors such as some GPS and sonic rangers with
baud rate below 38400 will report full sensor accuracy.
Smart track uses force gauges to
sense the location of a cart on a
track and displays it on LCD or
emulates a Vernier sonic ranger.
Center of mass visualizer uses force
gauges to sense x,y of center of
mass and sends to a PC, which then
overlays the location on live video.
10DOF project uses a $13
sensor board with 3-d
accelerometer, 3-d magnetic
sensor, 3-d gyroscope and
barometer and Bluetooth
wireless to relay data to PC.
• Our design is solid, easy to build and compatible to many sensors.
• The accuracy is more than sufficient for student labs
• The new design and ready-to-use enclosure drastically reduced
time and complexity to build a unit by a beginner
• The wireless connectivity offers lots of project opportunities
• We will develop lab activities and procedures for instructors
• We will test more sensors and write code for OSPL to use them
• We will develop more sample project codes for DIY projects
• We will seek funding to promote the OSPL