compiled". Likewise, ASYST-defined words are opaque, making it impossible for the casual user t o uncover and learn about ASYST algorithms. If such algorithms are to he taught, then custom words should he defined from the simple primitives available in ASYST or a lower-level language such as Basic should he used. Another potential prohlem with ASYST is its cost. Each module of ASYST costs about $500. Hardware costs are significant also with data acquisition hoards running from about $400 to $1200 (Data Translation); the 8087 chip can he obtained for less than $100. In summary our experience with ASYST has shown that i t can he learned by undergraduates and used in a simple data acquisition project which requires a minimum of programming effort yet invokes powerful data acquisition and analysis routines.
face hoard to the TRSdO Model I, the analog-to-digital converter (ADC) interface board, the parallel digital I/O interface hoard, the dual digital-to-analog converter (DAC) interface hoard, and the emulator console were designed and built in-house. The ADC interface hoard is used to determine the positions of variable controls by converting the appropriate voltages from potentiometers. The conditions of on/off and multiple position switches are read through the parallel digital I/O interface hoard. The microcomputer uses this information t o calculate what the signal output should he for these conditions and outputs appropriate voltages to an x-y recorder through the DAC interface hoard. A
A Microcomputer-Controlled T-60 NMR Emulator Gary D. Howard and Thomas D. DuBols University of North Carolina at Charlotte Charlotte. NC 28223 An insufficient numher of major instruments is a continuing prohlem in laboratory courses emphasizing instrumental methods. This prohlem is particularly severe in instrumental analysis courses where hands-on practice in adjusting and tuning the individual instruments is an important component of the lahoratory experience. Most small and medium-sized chemistry departments have a t most one of each of the major types of instruments. Some larger departments have more than one instrument of a given type available for instruction; however, the student/instrument ratio may be higher than that in the smaller institutions. Various approaches have been tried in an attempt to circumvent this prohlem; however, these approaches produce other undesirahle situations. The rotating experiment approach, in which different groups of students eachuse different instruments concurrently and rotate among them throughout the duration of the course, solves the student/ instrument ratio prohlem hut permits very little coordination between lecture and lahoratory. The open lahoratory approach also satisfies the studentlinstrument ratio prohlem hut requires an unreasonable numher of faculty instruction (contact) hours even if the instructor is not present in the lahoratory all of the time. Computers running simulator programs, where students use a keyboard t o enter values corresponding to control adjustments, have also been used in an attempt to relieve the situation. Some of these programs are quite instructive; however, there is little transference of this keyboard experience to adjusting and tuning an instrument using switches and knobs which have different sensitivities. As lahoratory instruments become more highly automated with the transfer of control and tuning functions to keyboards, this approach will become increasingly effective. However, most chemistry departments do not use the latest models of instruments for instruction. In an attempt t o solve this prohlem we have hegun to develop microcomputer-controlled instrument emulators. An instrument emulator resembles the actual instrument with the same type of controls arranged in a similar configuration. I t adjusts, tunes, and responds in the same way as the instrument which it emulates. We have recently developed and tested a Varian Model T-60 NMR emulator. A TRS-80 Model I microcomputer modified t o allow for port-addressed and memory-mapped 110and equipped with an expansion interface and dual disk drives was used t o develop the Varian T-60 NMR emulator (Fig. 5). The hardware requirements include a 13-hit ADC with eight multiplexed inputs, 48 parallel 110 lines, two 10-hit DAC's, eight potentiometers, one rotary switch, five sets of push-button switches, two lever switches and an x-y recorder. The inter-
Figure 5. T-00 NMR Ernuiatw mnsole.
I N I T I A L DIALOG
I
I
-
S E T VARIABLES
PARAMETERS
1
e RFAn CONTROL SETTINGS
INTEGRATE ROUTINE
I
nllTPllT X AKli Y VOLTAGES
I I
Figure 6. Software logic flow. Volume 63
Number 8
August 1966
711
scrapped Varian A-60 NMR console was modified to resemble a T-60 console and all source code was written in Basic. sweep offset (O), The values for the vertical offset (V), phase ( O ) , and resolution (R)were determined using the general equation X = X.(X, - X,) where X is the value used in the signal equation, X, is the scaling factor, X , is the offset, and X , is the voltage reading of the corresponding potentiometer. The value for the T 2 relaxation time (T)is calculated with the equation 1/T = (1 R)(L/2)'/2where L is the line width of the particular hydrogen nuclei for which the spectrum is being calculated. The Rf power (HI is calculated with the equation H = HAH./500) where H. is a scaline factor and H. is the voltwe - - * . .. read from the potentiometer copresponding td the ~f power control. The voltaee drivine the pen alone the x axis a t time voltage ( X , - 1) n ( X , ) is calculat~dbased i n the using the equation X , = XaW1 Sr/St where S, is the sweep rate and St is the sweep time. The corresponding frequency
of the rotating field a t time n (W,,) is calculated from the 0 Z - 3 where S, is the equation W, = ( X , - 77)& sweep width, 0 is the sweep offset, and Z is the zero offset. The value of the voltage sent to the Y input ( Y ) is calculated from the equations
+ +
y' =
Figure 7. Keyboardoptlms
- (W,- W)d.Sint)
1+(w,-W)2zQ+P.zQ
+
+
H.T.T,.CS.(Cost
where T . is a scaline factor. C is the concentration of the hydrogen nuclei. S isihe signal amplitude, IV, is the Larmor freuuencv of the hydrogen nuclei and I
