Cyclic Voltammetry Circuit Design Temperature Detection 2017-08-08¢ Cyclic Voltammetry...
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Cyclic Voltammetry Introduction
Cyclic voltammetry is a type of potentiodynamic electrochemical measurement. It provides an fast and simple method for initial characterization of a redox-active system. One of the main advantages of cyclic voltammetry compared to directly measuring initial reaction rate is that the pattern is reproducible and stable. This characteristic eases the measuring and recording process.
Figure1: Voltage waveform applied Figure2: Typical cyclic voltammogram
Experiment A test experiment was performed to testify that cyclic voltammetry was valid.
Figure 3 demonstrates the experiment circuit.
Figure 4 shows the voltage applied between counter and reference (yellow), and that across the resistor (purple) measured directly by oscilloscope. Figure 5 is the cyclic voltammogram generated by the oscilloscope.
Figure 4 Figure 5*
*: The voltammogram differs from the typical cyclic voltammogram since the test strips available, Accu-Chek, apply step function instead of triangular wave function. However, this technique is valid for OneTouch strip in the market, whose price is beyond our budget. Thus all tests are done using Accu-Chek strips, and OneTouch strips will displace Accu-Chek in the end.
Requirements In this project, an MSP430 chip is used as central control, and an external DAC is also applied as a voltage generator. In order to achieve cyclic voltammetry, the following requirements must be satisfied:
- able to measure and record voltage - able to generate triangular wave voltage
Design The MSP430 control chip sends commands to DAC using SPI (Serial Peripheral Interface) bus. The connections between two devices are shown below.
Figure 6 (above): Connection configuration Figure 7 (right): Test circuit on breadboard The voltage waveform generated by DAC is a smooth triangular wave (shown in Figure 8), whose frequency, offset, and peak to peak value are adjustable at software level. Meanwhile, the voltage measuring and storage take place with a suited frequency. Data can be transmitted into iPhone through audio jack and be analyzed instantly.
Figure 8 Figure 9: experimental data obtained from MSP430 and analyzed by Excel
The concentration is dependent on the vertex of cyclic voltammogram. The next step is to calibrate the glucose meter by processing data using iPhone application.
Thermopile An additional function is temperature detection for higher accuracy. A thermopile is used for contactless temperature measurement. It transfers the heat radiation emitted from the objects into a voltage output. The temperature sensing circuit contains a surrounding temperature compensating means and an amplifying means.
Figure 10 (above): Configuration of a temperature sensing circuit Figure 11 (right): Test circuit on breadboard
The output voltage is proportional to the detected temperature. A simple calibration is done with the circuit shown in Figure 11. Below shows the relationship between Vout and temperature. In the temperature range 31°C~46°C they are linearly related. Vout can be digitalized by an ADC and transmitted into iPhone. With the Figure 12 formula in the chart, the program can calculate the corresponding temperature and use as a reference for further analysis.
Temperature Detection Circuit Design
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References 1. Coutinho, C. F. B., Coutinho, L. F. M., Lanças, F. M., Câmara, C. A. P., Nixdorf, S. L., &
Mazo, L. H. (January 01, 2008). Development of instrumentation for amperometric and coulometric detection using ultramicroelectrodes. Journal of the Brazilian Chemical Society, 19, 1, 131-139.
2. Michigan State University Cyclic Voltammetry. Retrieved from http:// www2.chemistry.msu.edu/courses/cem419/cem372cyclicvoltammetry.pdf