A Triangle Wave Generator for Electrochemical Applications
W. E. Britton, R. H. Fleming, G. S. Hammond, and William
Nichparenko
University of Calitornia at Santa Cruz 95064
Electrochemical syntheses have been carried out for almost two centuries. However, until recently most of these studies were conducted in aoueous solutions nrecludine the examination of many potentially interesting organic compounds (1-3). With the advent of more sophisticated electronics it is now possible to carry out electrochemical synthetic and mechanistic studies in more resistive organic solvents (4, 5). Unfortunately, commercial instrumentation is often prohibitively expensive (6), and even home-built equipment priced in the range of several hundred dollars can discourage the occasional enthusiast. A routine, or even a more detailed organic electrochemical analysis should include cyclic voltammetry. This requires a signal generator at least capable of generating symmetrical triangle waves with both the initial and final potential adjustable independently of each other, and independently of the scan rate or direction. The scan rate should be variable from about a hundred millivolts to several hundred volts per second with the capability of selecting either a ramp and hold, a single sweep, or a multiple sweep triangle wave (7,8). We wish to describe such a signal generator which, in conjunction with a current-voltage booster (61, would provide one with a research grade instrument. A number of wave generators have been described (8, 9a-g), hut are more complex electronically and are several times more expensive (in part because they provide other functions not generally required or performed by organic electrochemists (10)). The block diagram shown in Figure 1 illustrates the operating principles of our wave generator. The "source" provides a positive and a negative potential, the amplitude of which is set by a voltage divider, "duldt control." Depending upon the state of the FET "switch," a positive or a negative level from the source is selected and delivered to the "integrator" initiating either a positive or a negative ramp, respectively. When the ramp voltage reaches a preset value, a level from the "comparator" induces the "flip-flop" to change states causing the switch output to change polarity. This series of events initiates another ramp a t the integrator, but with opposite slope. The continuation of these processes results in the generation of a series of triangle waves. With the incorporation of a simple logic circuit and a few switches, one can preselect the initial slope polarity, and choose from a ramp and hold signal, a single triangle wave, or a series of triangle waves. Figure 2 is a schematic diagram of the wave generator. A oower s u ~ ~schematic. lv a comolete parts list. and a more ketailed &fription of the wavcgene;ator may be obtained hv writine to the authors. The complete system including the powe; supply and chasis can be consiructed for less than $100.
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Acknowledgment
This work was supported by the U S . Army Research Office. Durham. North Carolina and Chevron Research Corporation, whom we thank.
68 1
Journal of Chemical Education
Figure 1. Black diagram
w
of wave generator.
A l , A2
dual o p a m p
A3 A4. A 5
FET op amp dual a p a m p
Gl.G2 G3. G 4 $1 CI,C3 C2
CD4Ol I A E 1H5018 0.1 p F
I OPF
R1. R 7 . R 1 0
10K. lo-turn
R2. R 3
1 3 3 K . 1% 1 1 8 K , 1%
R4. R 5 R6. R 8 . R 9 . R 1 1 R12. R13. R14 R15
triple 3-input nand gate quad 2-input nand gate dual F E T switch
1 0 K . 1% lOOK 22M
Figure 2. Wave generator schematic
Literature Cited ill Fry, A. J., "Synthetic OrganicElecfrochemi~fry."Harper sndRow,NewYork, 1372.
" "+* ". 121 Weinhen. N.L..Chem. T e c h . 4. 181 113741. 13) Mann, C. K.. and Rarnes. K. K.. "Electrochemical Reactions in Nonaqueous Systems: Marcel Dekker. New Ysrk. 1970. id1 Reierence l i ) . p . I. 161 ReierenceiS).p. 15. 161 Wmdward. W. S., Ridpvay.T. H..and Reilley, C. N..Anol C h e m . 45.435 1197:ll. 171 Reference I l l , p. 120. (8) Li.Chia-yu.Ferrier, D.. Schrueder,R. R..T h e m Instrum.. 3.333 113721. 191 is1 Cmnsr. C. I..Buehrna, G . H.. Johnson. C. J.. Pool. K. H.. Anal. Chem.. 45.417 119791: ibl B i r h a ~E..Hitchcock, P. H.. Anolyrl (London), 98. 165 11973); Icl Janala. J.. Lob. f'raci.. 20. 865 1137LI: (dl Neilren. C. J.. Staarr. .I. D.. Anal Chem., 44, 1719 119721: 1.) Bartak, D . E..Hundloy. H . K., Van Svaay. M.. Hawley, M.D., ('hem. Inrrrum.. 4, 1119721: i f ) Tsuji. K..Tskaharhi. I
