**5. Conclusions**

An Arduino-based pressure-sensor insole was prototyped for assessing flatfoot by choosing a suitable software and hardware architecture from measuring to receiving and designing a simplified self-made measurement plantar pressure instrument. After defining the position of the arch sensors relative to the length of the insole, which served as the placement rule of the sensors at the arch, the effectiveness of different sensor placements and flatfoot type assessment were tested during static and dynamic trials. By performing a correlation between traditional AI and the value of the self-made insole-based sensors with different sensor-placement options, and by comparing whether there were significant differences between the sensors at specific positions of flatfoot and normal foot from the data of 21 young subjects, it was found that during both the static and dynamic tests, the self-developed prototype could determine most of the flatfoot subjects and the most effective plantar pressure sensor position was also determined. Thus, in addition to the traditional subjective judgment of doctors, expensive X-ray detection, or judgments using a conventional ink-type area, the low-price insole-type measurement, including both static standing and dynamic waking, testing could be another wearable tool that reflects the medial longitude arch of the foot. It is suggested that in the future, this device can be applied in the insoles to examine the AI of the foot in clinical purposes due to its advantages when compared to the expensive-high tech graphic input board and conventional tools.

**Author Contributions:** All authors contributed to the preparation of the manuscript and data analysis. J.-W.C. completed the data collection.

**Funding:** The authors gratefully acknowledge financial support from the grant partly from the Ministry of Science and Technology, Taiwan (107-2410-H-011 -022 -MY3 to W.-C.H.).

**Acknowledgments:** The authors acknowledge all the participants in this study and the research students Cheng Wu Lin and Pai-En Yang for the data collection and analysis. The authors would like also to thank Li-Fong Lin and Jia-Lin Wu for providing clinical comments during this study.

**Conflicts of Interest:** The authors declare that there are no conflict of interest in this study.

**Ethical Statements:** All subjects gave their informed consent for inclusion before they participated in the study. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of National Chengchi University (NCCUREC201804E013).
