of oreanic solvents. dissociation constants of acids, indicator pH ;nges, transport number of H+, molar ionic conductivities. standard half cell potentials, solubilities, and activity coefficients. The database is menu driven, each new additional table heing added to the contents display and becoming accessible to all future users of the database. The students are marked on accuracy of the tabulated data, whle layout, inclusion of correct units, mention of any relevant conditions, and reference to the source of the data. Thus not only does the exercise provide an opportunity to apply programming skills but it also serves as an introduction to computerized databases; i t combines library work with experience in selecting appropriate data and accurately reporting all relevant conditions applying to the data, and also it acts as a prompt to encourage making reference to literature values in their laboratory reports. The author will be pleased to supply further details on request.
A Microcomputer-Based Temperature Probe Chla-yu Lil and Oun-meng Zhuang East Carolina University Greenville, NC 27834 A circuit interfacing a temperature probe with an APPLE IIe comauter has been develoaed. The maior com~onents used in {he circuit consist of adheatstone bridge, twb operational amalifiers. an eiebt-bit intenratinn analoeue-to-dipitalconveier, anda pro&ammable 6520~&iphe&Ilnterf&e Adapter. A silicon transistor whose metal casing is used as the temperature sensing probe forms one arm of the Wheatstone bridge. The impedance between the collector and emitter of the transistor varies as temperature changes, thus creating an imbalance of the bridge. The hridge output is amplified by the op amps and digitized by the ADC before it is sent to the computer's peripheral I/O slot. The temperature response between 0 and 100 OC is extremely linear (correlation coefficient = 0.99994) with a resolution of 0.39 "Clstea. Better resolution can be achieved if calibrated with a narrdwer temperature range. The device has been successfullv used for the determination of the specific beats of metals. The same circuit can also be used as a digital data acquisition device for low-frequency analogue signals (maximum sampling rate 2 mshyte). Short machine language programs, whichare callable by BASIC,are required to drive the interface circuit. Full details are available from Project SERAPHIM.
Microcomputer-Controlled Automated Sampler Shahrokh Ghaftari Mount Mary College Yankton, SD 57078 As a Dart of a microcom~uter-AFinterfacinn proiect, an automa'ted sampler for t h e nebulizer of an atomic fluorescence s~ectrometerwas desinned. This sampler is designed fur a two-solution system (hiank/sarnple) and is ideal when alternate blank/sample measurements are desired. The introduction of each solution into the flame is controlled by the software. The system is simple and easy to build and has applirations in other interfacing projects such as an auto-buret for titration or for introductionof reactants into a cell for a reaction study. The three parts, A, B, and C (Fig. 2) are installed inside a 5" X 8" X 4" aluminum box; no other parts except tubing are required. Auihor to whom correspondence should be addressed. 344
Journal of Chemical Education
Flgure 2. Schematic of components for automated sampler. A. SPST microcube solidstaterelay switch: Grayhill, Inc.. 561-T Hill Grove Ave.. Box 10373, La Grange, IL 60525. 8. Three-way solenoid valve: Serlal number H02-726 Skinner Precision Ind.. Inc.. 95 Edgewwd Ave., New Britain, CT 06050. C. Three-way slide valve: Dianex Co., P. 0.Box 3603, Sunnyvale,CA 94088.
Figure 2 shows a single-pole single-throw relay switch is used to turn on and off the ac power to the three-way solenoid valve. The solid-state relay is controlled by one 1iO line, which goes through a TRI-STATE buffer (not shown) before going to the contiol input of the relay. A logic 1signal on the I10 line switches on the relay and hence the solenoid valve that directs air (-40 PSI) to a three-way slide valve. The slide valve moves, and this causes the output of the slide valve to be connected to innut 1 (blank). The output of the valve is connected to the b k e r nebul'er with 0:5 mm i d . tubinn. When a loaic 0 sianal is connected to the control input; the output of the solenoid valve is connected to the atmosphere and the output of the slide valve is connected to position 2 (sample) through action of a spring.
A Simple Electronic Interface for Wlreless Chemical Data Communications Lee Hln-Fat, Hln-Cheung Lee, Kuen-Cheong Au-Yeung, and Hon-Tsang Chan Hong Kong Baptist College 224 Waterloo Road. Kowloon, Hong Kong Many undergraduate students may be interested in learnine the orinciales and the aoolications of electronic interfaces in wireless chemical data communication. A preliminary project that attempts to satisfy this interest has been carried out by our students. Data obtained from an iodine clock reaction were transmitted in the form of electromannetic waves to an Apple I1 microcomputer that had been connected to a wave receiver through an interface. The computer then calculated the order of the reaction. In order to make the svstem as inexpensive as possible, a minimum number of materials were &ed. The items involved included a phototransistor, a radio transmitter, and servo, all of which can be readily purchased from model or hobby shops. The output of the phototransistor was connected to a commercially purchased radio transmitter (Fig 3). The trimmer was set such that the output of the phototransistor under maximum ore-set lieht intensitv was eaual to that of " the maximum transmitter trimmer soltage. As a result, the trimmer of the ~hototransistortook over the function of the transmitter trimmer in the radio control. We used the signal intended to drive the motor in the servo as the inputio the receiver interface. The range of the input was e4V. The IC74CS14 interface used for this work was connected to one channel of the receiver as shown in Figure 4; neither amplification nor attenuation of the signal was necessary. In combination with the laboratory location where the preliminary transmission work was done, our system proved virtually impervious to interference that could
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