Technology Report pubs.acs.org/jchemeduc
Inexpensive Miniature Programmable Magnetic Stirrer from Reconfigured Computer Parts Conan Mercer* and Dónal Leech School of Chemistry and Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland S Supporting Information *
ABSTRACT: This technology report outlines a robust and easy to assemble magnetic stirrer that is programmable. All of the parts are recycled from obsolete computer hardware except the Arduino microcontroller and motor driver, at a total cost of around $40. This multidisciplinary approach introduces microcontrollers to students and grants the opportunity to interface basic computer programming with practical applications in chemistry. Utilizing the popular Arduino board empowers students to control laboratory devices, which in turn enhances enjoyment and understanding.
KEYWORDS: Upper-Division Undergraduate, Graduate Education/Research, First-Year Undergraduate/General, Interdisciplinary/Multidisciplinary, Computer-Based Learning, Hands-On Learning/Manipulatives, Instrumental Methods, Laboratory Equipment/Apparatus, Laboratory Computing/Interfacing, Student-Centered Learning
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INTRODUCTION
MAGNETIC STIRRER ASSEMBLY The stirrer assembly requires removal of neodymium magnets and brushless direct current (BLDC) motor from an obsolete computer disk drive. The neodymium magnets and BLDC can be found close to the optical assembly within any disk drive (Figure 1). The stirrer is assembled by placing neodymium magnets at the top of the BLDC, with the magnets retained
When a simple chemistry laboratory device is needed, arguably the best route toward understanding device function is building it in-house. The evolution in electronics results in rapid obsolescence of computers, and this provides an opportunity for reconfiguration and reuse of electronic components to provide cheap, effective, yet simple laboratory devices. We report a simple method to create a miniature microcontrolled magnetic stirrer from obsolete disk drive parts that can be assembled in less than 3 h, ideal for use in research and laboratory teaching. The device is inexpensive and suitable for adoption in undergraduate/graduate laboratories because of its miniature size, simple assembly and adaptability, and microfluidic platforms. The usefulness of programmable devices and microcontrollers in chemical education is well established,1−3 with in-house fabricated equipment such as photometers,4,5 colorimeters,6 syringe pumps,7 pH meters,8,9 PCR thermal cyclers,10 data acquisition devices,11 and potentiostats,12,13 proving inexpensive relative to use of desktop computers and commercial instruments. These low cost, simple instruments permit a 1:1 device to student ratio that can redefine the learning experience and support students through hands-on design and construction.14,15 A recent report demonstrated use of recycled computer parts to produce a magnetic stirrer, with the option of heating.16 However, the device is complex, requiring assembly of more than 35 parts, and it is not programmable. Herein, we describe a miniature, lightweight, durable, programmable magnetic stirrer assembled at low cost from readily available components and does not require advanced fabrication. © XXXX American Chemical Society and Division of Chemical Education, Inc.
Figure 1. Scheme showing disassembly of a conventional disk drive from a computer: (1) removal of outer protective sheath to expose internal components and (2 and 3) where to retrieve neodymium magnets and BLDC. Received: March 8, 2017 Revised: April 12, 2017
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DOI: 10.1021/acs.jchemed.7b00184 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
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Application of Magnetic Stirrer to Microfluidic Devices
through magnetic interaction with the metal motor. Importantly, the magnets do not interfere with internal electromagnets responsible for the motion of the motor. The motor weighs 38 g and has a diameter and a height of 23 mm.
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The capability of the fabricated magnetic stirrer is demonstrated by application to a microfluidic device. The device consists of a chamber created by cells defined using two polydimethylsiloxane (PDMS) gaskets sandwiched between two machined poly(methyl methacrylate) (PMMA) plates holding in each a tiny magnetic stir bar (Figure 3). When
Figure 2. Scheme showing the Arduino board, the motor driver, the electric pins of the motor, and all of the associated wiring.
Figure 3. Photograph showing the top view of the BLDC based stirrer embedded into a microfluidic device. Once the Arduino board is turned on, the BLDC motor spins and in turn stirs tiny magnetic stir bars contained within PDMS chambers.
MICROCONTROLLED MINIATURE MAGNETIC STIRRER The magnetic stirrer is controlled by an Arduino Uno board using an ATmega328P microcontroller. The Arduino is interfaced with the BLDC motor via an L293D driver which provides bidirectional driving currents up to 600 mA, within a voltage range of 4.5 to 36 V. The wiring of all components is achieved as detailed in Figure 2. Each BLDC winding is
screwed tightly together, this assembly forms an oval cylindrical channel 1.5 mm wide, 1.8 mm thick, and 100 μL in volume. The top PMMA plate includes ports to connect 0.2 mm i.d. PEEK tubing at inlets and outlets. The PDMS is an inexpensive compound that is simple to use and ideal for fabricating small numbers of devices, for example, in an educational institute. PMMA is a transparent thermoplastic often used to replace glass in microfluidic fabrication. The stirrer can be secured to almost any structure either using screws or fast setting glue. A list of the materials used is provided as Supporting Information section 5.
actuated in a sequential manner by application of 5 V, causing the rotor to turn in a rotating field. The actuation is achieved using an Arduino code as detailed in Supporting Information sections 1 and 2. A detailed description of BLDC motor theory and circuity is also provided as Supporting Information sections 3 and 4.
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HAZARDS
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Electrical Safety
The circuit used in this design uses a low voltage and does not pose a risk of electrical shock; however, it is good practice to adhere to appropriate electrical safety precautions. No electrical wires or components should be exposed, and electrical tape can be used to insulate any exposures. The magnetic stirrer should be assembled away from flammable materials, and it should be noted that any solutions containing ions conduct electricity and can short circuits.
CONCLUSION The assembly and operation of the magnetic stirrer fulfils two purposes: it provides an opportunity for students to learn basic programming by specifying actions to be executed, and it provides a set of concepts to use when thinking about what can be done to apply technology toward chemistry. This type of system should be especially helpful to common chemistry tasks in an undergraduate/research laboratory with low resource requirements.
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PROGRAMMING PRINCIPLES Simplicity was an important design criterion: the code to run the stirrer uses only the mandatory setup() and loop() functions required by the Arduino board to run and a custom function statement, magnetstir(); see Supporting Information section 2. Revolutions per minute (rpm) is varied by changing the delay time between each commutation sequence, lines 25, 29, 37, 41, 45 of the code. Decreasing or increasing time delays increases or decreases rpm, respectively. The amount of time the stirrer is active is easily programmed using millis() functions, lines 14 and 17 of the code. This permits many variations of time and rpm to be programmed and uploaded to the device.
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.7b00184. Schematic of breadboard to Arduino wiring, schematic of L293D pin out, schematic of conventional BLDC motor, and figure of Arduino PC interfacing (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. B
DOI: 10.1021/acs.jchemed.7b00184 J. Chem. Educ. XXXX, XXX, XXX−XXX
Journal of Chemical Education
Technology Report
ORCID
Conan Mercer: 0000-0003-3508-696X Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank Science Foundation Ireland for funding received under the US/Ireland programme (Grant Number 13/ US/B2546).
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REFERENCES
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DOI: 10.1021/acs.jchemed.7b00184 J. Chem. Educ. XXXX, XXX, XXX−XXX
