The inherent advantages of Visible Light Communication (VLC), such as high throughput and security,
has heightened the interest among researchers in studying it, especially in terms of Visible Light
Positioning (VLP). The research has resulted in excellent positioning systems and algorithms with a
centimetre localization accuracy. However, most researchers focus on presenting their newly designed
algorithms instead of describing and analyzing the utilized workspace and testing environments.
Moreover, most papers build use-case specific testbeds. The system implementation and hardware
features affect the VLP system’s performance and cost, and determine its applicability in the
commercial sphere. This thesis involves a VLC transmitter node, including electrical simulations and
electrical and thermal measurements. The study shows the realization of a node and the testing
environment.
Meanwhile, categorizing the node and theoretically evaluating all recent and available positioning
algorithms makes the node easily modifiable and adaptable.
The second objective of the research is to select a proper VLC receiver and construct a robotic
platform. This paper proposes a robotic device based on an ESP32 microcontroller. The robot
integrates a light sensor, enabling VLP and navigation algorithms testing. The designed firmware
collects the sensor’s data and controls the robot wirelessly.
Lastly, all gathered data and the robot’s controls are accessible through a web browser application.
The research in collaboration with Suda, M. processes the gathered image data. The web application
utilizes the architecture designed by Suda, M.

The inherent advantages of Visible Light Communication (VLC), such as high throughput and security,
has heightened the interest among researchers in studying it, especially in terms of Visible Light
Positioning (VLP). The research has resulted in excellent positioning systems and algorithms with a
centimetre localization accuracy. However, most researchers focus on presenting their newly designed
algorithms instead of describing and analyzing the utilized workspace and testing environments.
Moreover, most papers build use-case specific testbeds. The system implementation and hardware
features affect the VLP system’s performance and cost, and determine its applicability in the
commercial sphere. This thesis involves a VLC transmitter node, including electrical simulations and
electrical and thermal measurements. The study shows the realization of a node and the testing
environment.
Meanwhile, categorizing the node and theoretically evaluating all recent and available positioning
algorithms makes the node easily modifiable and adaptable.
The second objective of the research is to select a proper VLC receiver and construct a robotic
platform. This paper proposes a robotic device based on an ESP32 microcontroller. The robot
integrates a light sensor, enabling VLP and navigation algorithms testing. The designed firmware
collects the sensor’s data and controls the robot wirelessly.
Lastly, all gathered data and the robot’s controls are accessible through a web browser application.
The research in collaboration with Suda, M. processes the gathered image data. The web application
utilizes the architecture designed by Suda, M.

[1] D. Dardari, P. Closas and P. M. Djurić, ‘Indoor tracking: Theory, methods, and technologies,’
IEEE Transactions on Vehicular Technology, vol. 64, no. 4, pp. 1263–1278, 2015. doi: 10.1109/
TVT.2015.2403868.
[2] R. Joseph and S. B. Sasi, ‘Indoor positioning using wifi fingerprint,’ in 2018 International
Conference on Circuits and Systems in Digital Enterprise Technology (ICCSDET), 2018,
pp. 1–3. doi: 10.1109/ICCSDET.2018.8821184.
[3] S. Sophia, B. M. Shankar, K. Akshya, A. C. Arunachalam, V. T. Y. Avanthika and S. Deepak,
‘Bluetooth low energy based indoor positioning system using esp32,’ in 2021 Third International
Conference on Inventive Research in Computing Applications (ICIRCA), 2021, pp. 1698–1702.
doi: 10.1109/ICIRCA51532.2021.9544975.
[4] A. Vena, I. Illanes, L. Alidieres, B. Sorli and F. Perea, ‘Rfid based indoor localization system to
analyze visitor behavior in a museum,’ in 2021 IEEE International Conference on RFID
Technology and Applications (RFID-TA), 2021, pp. 183–186. doi:
10.1109/RFID-TA53372.2021.9617265.
[5] A. Aldalbahi, M. Rahaim, A. Khreishah, M. Ayyash and T. Little, ‘Visible light communication
module: An open source extension to the ns3 network simulator with real system validation two
scenarios are used in the validation of the vlc module:’ IEEE Access, vol. PP, pp. 1–1, Oct. 2017.
doi: 10.1109/ACCESS.2017.2759779.
[6] S. Afifah, S. Angelina, P. Susamti, R. Priramadhi and D. Darlis, ‘Energy efficient transmitter for
guided indoor navigation using visible light,’ IOP Conference Series: Materials Science and
Engineering, vol. 434, p. 012 213, Dec. 2018. doi: 10.1088/1757-899X/434/1/012213.
[7] Y. Zhuang, L. Hua, L. Qi et al., ‘A survey of positioning systems using visible led lights,’ IEEE
Communications Surveys Tutorials, vol. 20, no. 3, pp. 1963–1988, 2018. doi: 10.1109/COMST.
2018.2806558.
[8] Š. Bosák, ‘Hw for indoor visible light positioning testbed,’ Bachelor’s Thesis, CTU FEE,
Technická 2, May 2020. [Online]. Available: http://hdl.handle.net/10467/87622.
[9] M. Suda, ‘Sw for indoor visible light positioning testbed,’ Bachelor’s Thesis, CTU FEE, Technická
2, May 2020. [Online]. Available: http://hdl.handle.net/10467/87626.
[10] S. Li, Z. Wang, L. Shi and X. Zhang, ‘Experimental indoor tracking testbed based on visible light
communication,’ in 2019 26th IEEE International Conference on Electronics, Circuits and Systems
(ICECS), 2019, pp. 129–130. doi: 10.1109/ICECS46596.2019.8965061.
[11] Ai-Thinker, ESP32-CAM, 2017. [Online]. Available: http://www.ai- thinker.com/pro_
view-24.html.
[12] Device classes. [Online]. Available: https://www.thethingsnetwork.org/docs/lorawan/
classes/.
[13] STMicroelectronics, I-NUCLEO-LRWAN1, Original product from USI in partnership with
STMicroelectronics., 2018. [Online]. Available:
https://www.st.com/resource/en/data_brief/i-nucleo-lrwan1.pdf.
[14] M. Suda, ‘Infrastructure of indoor vlp system,’ Master’s Thesis, NTUST DECE, Taipei, Taiwan
(R.O.C.), Jun. 2022.
[15] STMicroelectronics, B-L072Z-LRWAN1, The B-L072Z-LRWAN1 LoRa/Sigfox Discovery kit is a
development tool to learn and develop solutions based on LoRa, Sigfox., 2019. [Online]. Available:
https://www.st.com/en/evaluation-tools/b-l072z-lrwan1.html.
[16] A. Devices, ADG819BRTZ-500RL7, Original product from Analog Devices., 2012. [Online].
Available: https://cz.mouser.com/datasheet/2/609/ADG819-1503098.pdf.
[17] T. Instruments, UA741CD, Original product from Texas Instruments., 2018. [Online]. Available:
https://www.gme.cz/data/attachments/dsh.310-515.1.pdf.
[18] VISHAY, IRF710, Original product from VISHAY., 2011. [Online]. Available: https://www.
gme.cz/data/attachments/dsh.213-180.1.pdf.
[19] AD817. [Online]. Available: https : / / www . analog . com / media / en / technical -
documentation/data-sheets/AD817.pdf.
[20] I. Rectifier, IRF540NPBF, Original product from International Rectifier., 2011. [Online].
Available: https : / / www . infineon . com / dgdl / irf540npbf . pdf ? fileId =
5546d462533600a4015355e39f0d19a1.
[21] Parasitic oscillation and ringing of power mosfets, Jul. 2018. [Online]. Available: https://www.
google . com / url ? sa = t & rct = j & q = &esrc = s & source = web & cd = &cad = rja & uact = 8 &
ved=2ahUKEwjWiY6SmPL1AhUQjVYBHesnDUAQFnoECA4QAw&url=https%5C%3A%5C%2F%5C%
2Ftoshiba . semicon - storage . com % 5C % 2Finfo % 5C % 2Fdocget . jsp % 5C % 3Fdid % 5C %
3D59456&usg=AOvVaw1QFazvSVKwhRVd6-XnKqUp.
[22] Ltspice: Stability of op amp circuits. [Online]. Available: https : / / www . analog . com / en /
education/education-library/videos/5579254320001.html.
[23] O. O. S. GmbH., LE UW U1A3 01, Original document from OSRAM Opto Semiconductors., 2018.
[Online]. Available: https://dammedia.osram.info/media/resource/hires/osramdam-
6715835/LE%5C%20UW%5C%20U1A3%5C%2001_EN.pdf.
[24] Ti precision labs-op amps: Stability-phase margin, Oct. 2021. [Online]. Available: https : / /
training.ti.com/ti-precision-labs-op-amps-stability-phase-margin?context=
1139747-1139745-14685-1138805-13849.
[25] C. Xie, W. Guan, Y. Wu, L. Fang and Y. Cai, ‘The led-id detection and recognition method based
on visible light positioning using proximity method,’ IEEE Photonics Journal, vol. 10, no. 2, pp. 1–
16, 2018. doi: 10.1109/JPHOT.2018.2809731.
[26] Rohde and Schwarz, ROHDE AND SCHWARZ RTM3000 OSCILLOSCOPE, 2022. [Online].
Available: https : / / www . rohde - schwarz . com / ae / products / test - and -
measurement/oscilloscopes/rs-rtm3000-oscilloscope_63493-427459.html.
[27] R. Semiconductor, Thermal calculation for linear regulator, 2017. [Online]. Available: https:
//fscdn.rohm.com/en/products/databook/applinote/ic/power/linear_regulator/
linearreg_heat_calculation_appli-e.pdf.
[28] T. Instruments, LM340T-12/NOPB, Original product from Texas Instruments., 2020. [Online].
Available: http : / / www . ti . com / general / docs / suppproductinfo . tsp ? distId = 26 &
gotoUrl=http%5C%3A%5C%2F%5C%2Fwww.ti.com%5C%2Flit%5C%2Fgpn%5C%2Flm340.
[29] M. WELL, RPS-30-12, 2021. [Online]. Available: https://www.meanwell- web.com/engb/
ac-dc-single-output-medical-open-frame-power-rps--30--12.
[30] X. Power, Iz series, 2021. [Online]. Available: https://www.xppower.com/product/IZSeries#.
[31] M. P. Solutions, Dc-dc converters, 2020. [Online]. Available: https://www.murata.com/-
/media/webrenewal/products/power/appnote/dcan-68.ashx?la=ja-jp&cvid=
20201014090810000000.
[32] BLM21AG102SN1#, 2022. [Online]. Available: https : / / www . murata . com / en - global /
products/productdetail?partno=BLM21AG102SN1%5C%23.
[33] B. Reeve, The capacitance multiplier, Feb. 2021. [Online]. Available: https://audioxpress.
com/article/the-capacitance-multiplier.
[34] D. Mercer, 16.3.1 transistor based capacitance multiplier, 2021. [Online]. Available: https :
//wiki.analog.com/university/courses/electronics/text/chapter-16.
[35] BCX54-16, 2017. [Online]. Available: https://www.nexperia.com/products/bipolartransistors/
general- purpose- and- low- vcesat- bipolar- transistors/singlebipolar-
transistors/single-bipolar-transistors-100-v/BCX54-16.html.
[36] BCX51/52/53, Aug. 2021. [Online]. Available:
https://www.diodes.com/assets/Datasheets/BCX51_52_53.pdf.
[37] Littlefuse, TPSMB150A-VR-TPSMB-VR series, Dec. 2020. [Online]. Available: https://www.
littelfuse.com/products/tvs- diodes/automotive- and- high- reliability- tvs/
tpsmb_vr/tpsmb150a_vr.aspx.
[38] T. F. LLC, FLIR E75, The product has been discontinued. Recommended replacement: FLIR E76.,
2021. [Online]. Available: https://www.flir.com/support/products/e75/#Overview.
[39] W. Thermal, Wakefield thermal 40x10mm 2 wire dc fan 12.2cfm —DC0401012V2B-2T0, 40mm x
40mm x 10mm 2 Wire DC Fan 12.2CFM. [Online]. Available: https://wakefieldthermal.
com/wakefield-thermal-40x10mm-2-wire-dc-fan-12-2cfm-dc0401012v2b-2t0/.
[40] P. Chen, M. Pang, D. Che, Y. Yin, D. Hu and S. Gao, ‘A survey on visible light positioning from
software algorithms to hardware,’ Wireless Communications and Mobile Computing, vol. 2021,
pp. 1–20, Feb. 2021. doi: 10.1155/2021/9739577.
[41] M. Nakajima and S. Haruyama, ‘New indoor navigation system for visually impaired people using
visible light communication,’ EURASIP Journal on Wireless Communications and Networking,
vol. 2013, Dec. 2013. doi: 10.1186/1687-1499-2013-37.
[42] C. Sertthin, T. Fujii, O. Takyu, Y. Umeda and T. Ohtsuki, ‘On physical layer simulation model
for 6-axis sensor assisted vlc based positioning system,’ in 2011 IEEE Global Telecommunications
Conference - GLOBECOM 2011, 2011, pp. 1–5. doi: 10.1109/GLOCOM.2011.6134119.
[43] Y. U. Lee and M. Kavehrad, ‘Two hybrid positioning system design techniques with lighting leds
and ad-hoc wireless network,’ IEEE Transactions on Consumer Electronics, vol. 58, no. 4,
pp. 1176–1184, 2012. doi: 10.1109/TCE.2012.6414983.
[44] S.-Y. Jung, S. Hann, S. Park and C.-S. Park, ‘Optical wireless indoor positioning system using light
emitting diode ceiling lights,’ Microwave and Optical Technology Letters, vol. 54, Jul. 2012. doi:
10.1002/mop.26880.
[45] Y.-S. Kuo, P. Pannuto, K.-J. Hsiao and P. Dutta, ‘Luxapose: Indoor positioning with mobile
phones and visible light,’ in Proceedings of the 20th Annual International Conference on Mobile
Computing and Networking, ser. MobiCom ’14, Maui, Hawaii, USA: Association for Computing
Machinery, 2014, pp. 447–458, isbn: 9781450327831. doi: 10 . 1145 / 2639108 . 2639109.
[Online]. Available: https://doi.org/10.1145/2639108.2639109.
[46] Z. Yang, Z. Wang, J. Zhang, C. Huang and Q. Zhang, ‘Wearables can afford: Light-weight indoor
positioning with visible light,’ Proceedings of the 13th Annual International Conference on Mobile
Systems, Applications, and Services, 2015.
[47] S. Yamaguchi, V. V. Mai, T. C. Thang and A. T. Pham, ‘Design and performance evaluation of
vlc indoor positioning system using optical orthogonal codes,’ in 2014 IEEE Fifth International
Conference on Communications and Electronics (ICCE), 2014, pp. 54–59. doi: 10.1109/CCE.
2014.6916679.
[48] P. Hu, L. Li, C. Peng, G. Shen and F. Zhao, ‘Pharos: Enable physical analytics through visible light
based indoor localization,’ Nov. 2013. doi: 10.1145/2535771.2535790.
[49] L. Li, P. Hu, C. Peng, G. Shen and F. Zhao, ‘Epsilon: A visible light based positioning system,’ 11th
USENIX Symposium on Networked Systems Design and Implementation (NSDI 14), pp. 331–343,
Jan. 2014.
[50] T. Q. Wang, Y. A. Sekercioglu, A. Neild and J. Armstrong, ‘Position accuracy of time-of-arrival
based ranging using visible light with application in indoor localization systems,’ Journal of
Lightwave Technology, vol. 31, no. 20, pp. 3302–3308, 2013. doi:
10.1109/JLT.2013.2281592.
[51] Y. H. Choi, I. H. Park, Y. H. Kim and J. Y. Kim, ‘Novel lbs technique based on visible light
communications,’ in 2012 IEEE International Conference on Consumer Electronics (ICCE), 2012,
pp. 576–577. doi: 10.1109/ICCE.2012.6161980.
[52] T.-H. Do and M. Yoo, ‘Tdoa-based indoor positioning using visible light,’ Photonic Network
Communications, vol. 27, pp. 80–88, Apr. 2014. doi: 10.1007/s11107-014-0428-4.
[53] A. Arafa, S. Dalmiya, R. Klukas and J. Holzman, ‘Angle-of-arrival reception for optical wireless
location technology,’ Optics Express, vol. 23, Mar. 2015. doi: 10.1364/OE.23.007755.
[54] M. Yasir, S.-W. Ho and B. N. Vellambi, ‘Indoor positioning system using visible light and
accelerometer,’ Journal of Lightwave Technology, vol. 32, no. 19, pp. 3306–3316, 2014. doi:
10.1109/JLT.2014.2344772.
[55] M. Yasir, S.-W. Ho and B. N. Vellambi, ‘Indoor position tracking using multiple optical receivers,’
Journal of Lightwave Technology, vol. 34, no. 4, pp. 1166–1176, 2016. doi: 10.1109/JLT.2015.
2507182.
[56] G. B. Prince and T. D. Little, ‘A two phase hybrid rss/ aoa algorithm for indoor device
localization using visible light,’ in 2012 IEEE Global Communications Conference
(GLOBECOM), 2012, pp. 3347–3352. doi: 10.1109/GLOCOM.2012.6503631.
[57] K. N. e. a. Hirokazu Nishikata Hideo Makino, ‘Basic research of indoor positioning method using
visible light communication and dead reckoning,’ International Conference on Indoor Positioning
and Indoor Navigation (IPIN), Sep. 2011.
[58] N.-T. Nguyen, N.-H. Nguyen, V.-H. Nguyen, K. Sripimanwat and A. Suebsomran, ‘Improvement
of the vlc localization method using the extended kalman filter,’ in TENCON 2014 - 2014 IEEE
Region 10 Conference, 2014, pp. 1–6. doi: 10.1109/TENCON.2014.7022416.
[59] E. O. Inc., Imaging electronics 101: Understanding camera sensors for machine vision
applications. [Online]. Available: https : / / www . edmundoptics . com / knowledge -
center / application - notes / imaging / understanding - camera - sensors - for -
machine-vision-applications/.
[60] W. Guan, Y. Wu, C. Xie, L. Fang, X. Liu and Y. Chen, ‘Performance analysis and enhancement
for visible light communication using cmos sensors,’ Optics Communications, vol. 410,
pp. 531–551, 2018, issn: 0030-4018. doi:
https : / / doi . org / 10 . 1016 / j . optcom . 2017 . 10 . 038. [Online]. Available:
https://www.sciencedirect.com/science/article/pii/S0030401817309458.
[61] W. Guan, X. Chen, M. Huang, Z. Liu, Y. Wu and Y. Chen, ‘High-speed robust dynamic positioning
and tracking method based on visual visible light communication using optical flow detection and
bayesian forecast,’ IEEE Photonics Journal, vol. 10, no. 3, pp. 1–22, 2018. doi: 10.1109/JPHOT.
2018.2841979.
[62] O. Technologies, Freertos real-time operating system for microcontrollers. [Online]. Available:
https://www.freertos.org.
[63] O. Technologies, Ov2460 color cmos uxga (2.0 megapixel) camerachip with omnipixel2
technology, Feb. 2006. [Online]. Available:
https://www.uctronics.com/download/cam_module/OV2640DS.pdf.
[64] O. Technologies, Ov7670/ov7171 cmos vga (640x480) camerachip with omnipixel technology,
May 2006. [Online]. Available: https : / / www . uctronics . com / download / Datasheet /
ov7670_full_datasheet.pdf.
[65] LaskaKit, Převodník 6pin usb ttl uart, cp2102, dtr pin. [Online]. Available:
https://www.laskakit.cz/prevodnik-6pin-usb-ttl-uart--cp2102--dtr-pin/.
[66] S. Studio, Image of ESP32-CAM. [Online]. Available:
https : / / www . seeedstudio . com / media / catalog / product / cache /
ef3164306500b1080e8560b2e8b5cc0f/b/a/bazaar1003541_esp32cam3.jpg.
[67] D. Kim, J. K. Park and J. T. Kim, ‘Three-dimensional vlc positioning system model and method
considering receiver tilt,’ IEEE Access, vol. 7, pp. 132 205–132 216, 2019. doi: 10.1109/ACCESS.
2019.2940759.
[68] Y. Li, Z. Ghassemlooy, X. Tang, B. Lin and Y. Zhang, ‘A vlc smartphone camera based indoor
positioning system,’ IEEE Photonics Technology Letters, vol. 30, no. 13, pp. 1171–1174, 2018.
doi: 10.1109/LPT.2018.2834930.
[69] D. Workshop, Build an esp32cam robot car, Apr. 2021. [Online]. Available:
https://dronebotworkshop.com/esp32cam-robot-car/.
[70] D. Inc., H-bridges, 2014. [Online]. Available:
https://learn.digilentinc.com/Documents/325.
[71] B. J. Jim Brown, Brief h-bridge theory of operation, Sep. 2002. [Online]. Available:
https : / / archive . ph / 20130112153214 / http : / / www . dprg . org / tutorials / 1998 -
04a/#selection-267.0-267.34.
[72] Toshiba, TB6612FNG, Jun. 2007. [Online]. Available:
https://www.sparkfun.com/datasheets/Robotics/TB6612FNG.pdf.
[73] MagiDeal, Magideal 1 piece dc geared motor, 3-6v tt gear motor, motor support/ bracket for
arduino diy robot smart car robot tool chassis (multicolor). [Online]. Available:
https://www.flipkart.com/magideal-1-piece-dc-geared-motor-3-6v-tt-gearmotor
- support - bracket - arduino - diy - robot - smart - car - tool -
chassis/p/itmf3h45ybkzbjzw.
[74] T. Instruments, Lm2596 simple switcher power converter 150-khz 3-a step-down voltage regulator,
May 2021. [Online]. Available: https://www.ti.com/lit/ds/symlink/lm2596.pdf?ts=
1649206965309&ref_url=https%253A%252F%252Fwww.google.com%252F.
[75] NooElec, 10 pcs lm2596 dc-dc buck converter step down module power supply output 1.23v-30v,
Jun. 2012. [Online]. Available: https://www.amazon.com/LM2596- Converter- Module-
Supply-1-23V-30V/dp/B008BHBEE0.
[76] diymore Store, Diymore esp32 cam ov2640 2mp w-bt camera module+2.4g extension cable 20cm
ipx adapter cable, Jun. 2019. [Online]. Available:
https : / / www . amazon . com / dp / B07T1PG77D ? tag = makeradvisor -
20&linkCode=ogi&th=1&psc=1.
[77] TOTOLINK, Ac1200, wireless dual band router, model no. a800r. [Online]. Available: https:
//www.totolink.net/home/menu/detail/menu_listtpl/products/id/166/ids/33.
html.
[78] T. Chip, 2wd smart robot car chassis kit. [Online]. Available: https://www.twinschip.com/
2WD_Smart_Robot_Chassis.
[79] Async web server for esp8266 and esp32, Mar. 2022. [Online]. Available: https://github.
com/me-no-dev/ESPAsyncWebServer.
[80] M. W. Docs, Http headers, Apr. 2022. [Online]. Available: https://developer.mozilla.
org/en-US/docs/Web/HTTP/Headers.
[81] M. W. Docs, Http request methods, Oct. 2021. [Online]. Available:
https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods.
[82] Ardunio, Millis(), Mar. 2021. [Online]. Available: https://www.arduino.cc/reference/en/
language/functions/time/millis/.
[83] L. Espressif Systems (Shanghai) Co., Led control (ledc), 2022. [Online]. Available:
https : / / docs . espressif . com / projects / esp - idf / en / latest / esp32 / api -
reference/peripherals/ledc.html#ledc-api-supported-range-frequency-dutyresolution.
[84] Esp32 camera driver, Licensed under the Apache License 2.0, Feb. 2022. [Online]. Available:
https://github.com/espressif/esp32-camera.
[85] D. Lane, Creating a multi-resolution favicon including transparency with the gimp, Aug. 2011.
[Online]. Available: https : / / web . archive . org / web / 20101225130900 / http :
//egressive.com/tutorial/creating- a- multi- resolution- favicon- includingtransparency-
with-the-gimp.
[86] B. Jan, Express.js tutorial, Oct. 2021. [Online]. Available:
https://zetcode.com/javascript/expressjs/.
[87] Freepik, Robot free icon. [Online]. Available: https : / / www . flaticon . com / free - icon /
robot_3662817?related_id=3662817&origin=search.
[88] B. Blanchon, Arduino json, 2022. [Online]. Available: https://arduinojson.org.
[89] tzapu, AsyncWiFiManager, Licensed under the MIT License., Jan. 2022. [Online]. Available:
https://github.com/alanswx/ESPAsyncWiFiManager.
[90] A. Sharma, AsyncElegantOTA, Licensed under the MIT License., Apr. 2022. [Online]. Available:
https://github.com/ayushsharma82/AsyncElegantOTA.
[91] I. Grokhotkov, Generic class, Licensed under the GNU Lesser General Public License v2.1,
2017. [Online]. Available: https : / / arduino -
esp8266.readthedocs.io/en/latest/esp8266wifi/generic-class.html.
[92] MDN, Json.stringify(), Licensed under a Creative Commons license, Mar. 2022. [Online].
Available: https : / / developer . mozilla . org / en -
US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify.