A Study on the Development of Arduino-Electrochemical Cell and the Exploration of Educational Possibilities from the Perspective of Learning by Making

The development process of the electrochemical cell using Arduino and sensor consists of the three phases of electric circuit construction, code, and performing experiment.

First of all, connect the Arduino Uno board, voltage sensor and metal plates. The overall device connection is as shown in Fig. 1.

A voltage sensor could be used to measure the voltage of the cell. In this experiment, a voltage sensor (SZH-SSBH-043) was used for the convenience. The voltage sensor (SZH-SSBH-043) was used to measure voltages between 0 and 25V. The electrical connections were made as follows. To measure the voltage of an electrochemical cell, connect the 'GND' part of the voltage sensor to the metal plate to be oxidized and then connect the 'VCC' part of the voltage sensor to the metal plate to be reduced. Connect the 's' terminal of the voltage sensor to 'A0' of the Arduino board, the '-' terminal of the voltage sensor to 'GND' of the Arduino board and the '+' terminal of the voltage sensor to '5V' of the Arduino board follows (Fig. 1).

Figure1.

Schematic of the electrical circuit.

The Arduino is controlled by code written with the microcontroller’s own programming tool known as the ‘Integrated Development Environment (IDE)’. The voltage entering VCC is represented by 'vin', and the voltage entering from S is represented by 'vout'. And if we express resistance 30k as R1 and resistance 7.5k as R2, then vin: vout = (R1 + R2): R2. The following code implies to read the voltage of the electrochemical cells.

 
void loop() { 
….. 
value = analogRead(analogInput);
vout = (value * 5.0) / 1024.0; 
vin = vout / (R2/(R1+R2)); …
.....
}

The experimental steps are as follows and Fig. 2 and 3 are schematics of the electrochemical cells using Arduino and sensor.

The serial and parallel connections of the Galvanic electrochemical cells are shown in Fig. 2. At this time, Fig. 3 shows the actual experimental photos of Galvanic electrochemical cells.

Figure2.

Series and parallel connection of Galvanic electrochemical cells.

Figure3.

Actual experimental photos of Galvanic electrochemical cells.

■ Galvanic Electrochemical Cells in Series

■ Galvanic Electrochemical Cells in Parallel

The serial and parallel connections of the Daniel electrochemical cells are shown in Fig. 4. At this time, Fig. 5 shows the actual experimental photos of Daniel electrochemical cells.

Figure4.

Series and parallel connection of Daniel electrochemical cells.

Figure5.

Actual experimental photos of Daniel electrochemical cells.

■ Daniel Electrochemical Cells in Series

■ Daniel Electrochemical Cells in Parallel

The inquiry activities using Arduino-electrochemical cells for students consisted of main and application activities. The main activities consisted of providing students with the basic knowledge and skills needed to conduct the Arduino-electrochemical cells experiment, such as information about electrical circuit connection and coding for 2 hours. And the main activities also consisted of students making their own electrochemical cells into the series and parallel connections, measuring voltages, and graphing voltage values for 2 hours.

The application activities consisted of students making some objects by using Arduino-electrochemical cells for 4 hours. Therefore, after conducting the main activities, the students were asked to make objects operating actuators by using the voltage difference between the serial and parallel connections of the Arduino-electrochemical cells as the application activities.

Meanwhile, the 8 students who participated in the inquiry activities in October 2018 were second-year students attending A high school in Seoul, Korea. The participants were volunteers who were taking chemistry classes and were organized into two groups for inquiry activities.

After the students completed inquiry activities, a semistructured follow-up interview was held with each student over a period of approximately 30 minutes. The contents of the follow-up interview included questions about the characteristics of the inquiry activities, and the reasons thereof. All the answers given by the students during the follow-up interview were recorded.

After having transcribed the entire contents of the follow- up interview, the contents of the students' responses were analyzed. At this time, a summative approach method of analyzing the qualitative contents with a focus on the meaning implied by the terminologies or contents in the students’ responses was used. As such, two analysts summarized the core contents of the students’ responses on coding paper in a single paragraph and key words were chosen from the core sentences. Moreover, the extent of concordance between the analysts was checked from the perspective of the key words. If the opinions of the analysts were not in concordance, the cause of the non-concordance was reviewed by reanalyzing the relevant data, and then a final decision was made through discussion. Moreover, analysts were instructed to present the representative contents of the response in the research results to enable clear assessment of the overall trends, responses, and characteristics of the answers the students gave.

We developed the electrochemical cell using Arduino and sensor, and experimented with ‘voltage change when connected in series’, and ‘voltage change when connected in parallel’ using this device. The results are as follows.

The complete cell consisted of copper and zinc electrodes partially immersed in diluted sulfuric acid. The surface of the zinc electrode readily dissolved in the sulfuric acid, and the zinc atoms combined with the sulfate to form zinc sulfate. In this process, the zinc atoms leave electrons behind them on the zinc electrode.

Oxidation: Zn → Zn²⁺ +  2_e⁻

Reduction: 2H⁺ + 2_e⁻ → H₂

As the zinc sulfate forms, hydrogen ions are released, and these ions travel to the copper electrode, where they acquire electrons.

When Galvanic electrochemical cells were connected in series, the total voltage was the sum of the voltage of the respective cells, or when Galvanic electrochemical cells were connected in parallel, the total voltage was equal to one voltage. When the electrochemical cells of each beaker were connected in series and the voltage was measured, it was observed that the voltage increased by two, and three, respectively. However, when electrochemical cells of each beaker were connected in parallel, it was observed that the voltage remained constant even if there were two or three electrochemical cells (Fig. 6).

Figure6.

Measured voltages of series and parallel connection of Galvanic electrochemical cells (Zn-Cu).

The complete cells consisted of copper and zinc electrodes partially immersed in copper sulfate solution and zinc sulfate solution, respectively. And, two half cells were connected with salt bridge. The spontaneous flow of electrons from Zn electrode to Cu electrode generates a current with a voltage near the theoretical value for these couples (1.10 V).

Oxidation: Zn → Zn²⁺ +  2_e⁻

Reduction: Cu²⁺ + 2_e⁻ → Cu

When Daniel electrochemical cells were connected in series, the total voltage was the sum of the voltage of the respective cell, or when Daniel electrochemical cells were connected in parallel, the total voltage was equal to one voltage. When the electrochemical cells of each beaker were connected in series and the voltage was measured, it was observed that the voltage increased by two, and three, respectively. However, when electrochemical cells of each beaker were connected in parallel, it was observed that the voltage remained constant even if there were two or three electrochemical cells (Fig. 7).

Figure7.

Measured voltages of series and parallel connection of Daniel electrochemical cells (Zn-Cu).

Therefore, the developed Arduino-electrochemical cells were found to be capable of accurate and fast data collection. In addition, it was possible to visually confirm the changes in voltage when the electrochemical cells were connected in series and parallel. And it was also confirmed that the Arduino-electrochemical cells could be easily coded and deformed.

After the students completed the main activity of making their own electrochemical cells in series and parallel connections and measuring voltage, the students were trying to operate actuators such as ‘fan motor’, ‘piezo buzzer’, and ‘RGB LED’ by using the voltage difference of the electrochemical cells as the application activity. In this activity, the students expressed in coding the voltage difference obtained from the Arduino-electrochemical cells to control the operation of the actuators. The following is an example of students' application activities. Meanwhile, among the inquiry activities, the students' results on the main activities of making Arduino-electrochemical cells and measuring voltage values were presented in the Supplementary Information materials.

Group 1 students operated the fan motor using the voltage difference of the electrochemical cells. To do this, the students constructed algorithms to rotate fans twice as fast if input voltage was greater than 1.2V, to rotate fans by one time if input voltage was greater than 0.6V and less than 1.2V, and to stop rotating if input voltage was less than 0.6V. (Theoretical values were 1.4 and 0.7V, but 1.2 and 0.6V were used for coding considering the experimental variation). The code and electrical connections (Fig. 8) are as follows.

Figure8.

Student-made object: Arduino-electrochemical cells with fan motor.

if (vin > 1.2){ 
   analogWrite(INA, 250); 
   analogWrite(INB, 0); 
   } 
   else if (vin > 0.6) { 
   analogWrite(INA, 125); 
   analogWrite(INB, 0);
   } 
   else { 
   analogWrite(INA, 0); 
   analogWrite(INB, 0); 
   }

Group 2 students operated the Piezo buzzer using the voltage difference of the electrochemical cells. In this students' activity, the algorithm was configured by adjusting the pitch of the sound from the piezo buzzer based on the voltage difference of the electrochemical cells. As an example, students constructed algorithms to sound G(sol) if input voltage was greater than 1.2V, to sound E(mi) if input voltage was greater than 0.6V and less than 1.2V, and to sound C(do) if input voltage was less than 0.6V. The code and electrical connections (Fig. 9) are as follows.

Figure9.

Student-made object: Arduino-electrochemical cells with piezo buzzer.

if (vin > 1.2){ 
   tone(piezo, 783);
   } 
   else if (vin > 0.6) { 
   tone(piezo, 659);
   } 
   else{ 
   tone(piezo, 523);
   }

Group 2 students also operated the RGB LED using the voltage difference of the electrochemical cells. In this student' activity, students set the voltage range to change the color of the RGB-LED according to the voltage range of the electrochemical cells. To do this, the students constructed algorithms to turn yellow-cyan-magenda color on in order if input voltage was greater than 1.2V, to turn red-green-blue color on in order if input voltage was greater than 0.6V and less than 1.2V, and to turn white on if input voltage was less than 0.6V. The code and electrical connections (Fig. 10) are as follows.

Figure10.

Student-made object: Arduino-electrochemical cells with RGB LED.

if (vin > 1.2){ 
   analogWrite(R,255); 
   analogWrite(G,255); 
   analogWrite(B,0); 
   delay(1000); 
   analogWrite(R,0); 
   analogWrite(G,255); 
   analogWrite(B,255); 
   delay(1000); 
   analogWrite(R,255); 
   analogWrite(G,0); 
   analogWrite(B,255); 
   delay(1000); 
   }

As such, students made some objects that could operate various actuators by coding the voltage differences of Arduino- electrochemical cells. Since series and parallel connections of the electrochemical cells give a different voltage, students could make objects for the operation of actuator using the difference of the output voltage. Thus, these activities not only helped students learn chemistry concept, but also provided them with the opportunity to test and apply the chemistry concept creatively in practice.

As a result of the students' perception on the electrochemical cell experiment using Arduino and sensor, it could be discerned that the experimental device can not only be helpful in enhancing student knowing and applying of scientific concepts, but also in naturally inducing communication and problem-solving discussion among students as a creative skill. The specific details of the results are as follows.

Students reported that the inquiry activity using Arduino- electrochemical cells helped them more effectively to understand the concept of science compared to traditional classes. In other words, the students mentioned that they were able to study the scientific concept on the basis of their understanding regarding the principles and phenomenon, rather than simply by memorizing them. As an example, Student C stated, “I was able to realize the difference between serial and parallel connection of electrochemical cells through changes in the voltage graph, rather than by having to simply memorize them.”

As to why the electrochemical cell experiment using Arduino and sensor was helpful in understanding the scientific concept above, students mentioned ‘immediate visualization of results’, ‘numerous re-experimentations’, and ‘free correction and editing of the program source code’. For example, Student A stated, “Unlike traditional experiments, experiment using maker elements showed me an error message when there was a problem with the experiment itself, and through this, I was able to reconsider the problems with the experiment and perform the experiment again. This process helped to understand the experiment more accurately, which in turn helped to understand the related theory more accurately.” Student B also stated, “Arduino was great to see the resultant values on the figures and graphs immediately”, and “when the graph was not drawn properly, I was able to solve the problem by re-executing the experiment or modifying the variables.”

Students were found to have a new perception of the existing science curriculum through this inquiry activities using Arduino-electrochemical cells. The students thought that science only uses what they learned in class to solve test questions, but this inquiry activity made them feel that science is closely related to their daily lives. In this regard, Student H stated, “Through this inquiry activity, I realized that science concepts could be applied to everyday life like a battery.”

Especially, the students thought that coding was recognized only as being used to develop apps, games or robots. However, after maker-based scientific inquiry activity, students thought that coding was recognized as being able to be applied to various fields to creating something, especially in integration among subjects. For example, Student C stated, “I thought that through scientific experiment using coding, coding could be linked to subjects such as mathematics and history, and it was fun to think about it.”

Students indicated that the inquiry activity such as making objects by using the electrochemical cell with Arduino and sensor was helpful in the communication and problem-solving process. In other words, the students commented that it was possible to have more meaningful communication and exchange of opinions during the making objects. For example, Student B mentioned that there was almost no discussion between classmates during performing experiment according to the experimental procedures and methods presented in the textbook. However, when conducting the application activity using Arduino and sensor, Student B indicated that there were exchanges of questions and answers between classmates in order to make objects. Namely, the students commonly responded that they pondered the principles of the scientific concepts, communicated with each other, and were able to solve problems through this making activity.

As to why the electrochemical device using Arduino and sensor was helpful for communication and the problem-solving process, visualization of scientific concept can be considered as the reason. In other words, the electrochemical device using Arduino and sensor is capable of fast collection and analysis of data, and visualization of such data. Moreover, the immediate feedback from this visual aspect can be seen to have led students to discuss the experimental contents and scientific concepts. In fact, Student A mentioned that the immediate and visual feedback provided by the Arduino experimental device was helpful in inducing a variety of questions and discussions among the students.

It was also shown that the characteristics of the electrochemical device using Arduino and sensor, which was easily programmable and easily adaptable to each situation, were helpful to students' problem-solving process. In other words, it can be interpreted that the ease of programming the Arduino experimental device and the flexible modification of the experimental device suitable for the given situation assisted with the direct execution of problem solving. In fact, it turned out that the students changed the experimental device freely and modified the source code easily in order to solve problematic situations during the experiment. For example, Student E mentioned, “After having confirmed that there was no electric current flow, I quickly changed the experimental method" and "I was able to produce my own experimental device through modification of the source code.”