SUGISAKAMASANORI

Journal of Advances in Artificial Life Robotics
Vol. 1(2); September (2020), pp. 71–75
ON LINE ISSN 2435-8061; ISSN-L 2435-8061
https://alife-robotics.org/jallr.html

Research Article

An FSK based industrial analog signal transmission
Po-Yun Shih1, Chung-Wen Hung1, Chau-Chung Song2

1
Department of Electrical Engineering, National Yunlin University of Science &Technology, 123 University Road, Section 3, Douliou Yunlin 64002,Taiwan
2
Department of Aeronautical Engineering, National Formosa University, 64 Culture Road, Huwei Yunlin 63201, Taiwan

ARTICLE INFOArticle History
Received 24 October 2019Accepted 24 July 2020
Keywords
FSK
Wireless
Industrial communication
Active filter

ABSTRACTAn FSK (Frequency-Shift Keying) based industrial analog signal transmission is proposed in thispaper. Due to the advantage of digital transmission, such as noise immunity and error check, thedigital transmission is more and more popular. The FSK is a simple kind of basic digitaltransmission. Although the analog signal modulation is already well-known and mature, but it iseasily interfered by the noise, especially in an industrial environment. When the carried frequency
is occupied, the alternative frequency is necessary. However, it is a tough work for sure. The FSK
based wireless transmission is used to perform a wireless transmission of analog signal in theindustry. It also has good effects of removing the wiring from device to device, and breaks therestriction of the device movement. Experimental results show that the proposed method can work
well, and the wireless transmission bandwidth achieves 16kHz.

© 2022 The Author. Published by Sugisaka Masanori at ALife Robotics Corporation Ltd.
This is an open access article distributed under the CC BY-NC 4.0 license(http://creativecommons.org/licenses/by-nc/4.0/).

robustness to channel impairments, easily multiplexingof various forms of information and detect and correcttransmission errors by accommodated digital errorcontrol codes.
Because of the reasons stated above, the goal on thispaper is put the eye on transmit the analog signal bydigital modulation. The paper is focused on the analog
signal because there are many continuous analog signal
on a machine, such as voltage, current or temperature of
the machine. [6] collects all the information to monitor
by digital wireless transmission, then the emergency
events are detected by comparing the original waveform.
In [7], the MCU is used to sample the analog signal fromsensors in the industrial environment, and the sampled
data are transmitted by the wireless signal to the masterfor monitoring. However, both of two papers neverdiscussed about reconstruction of signal.

1. Introduction
In recent years, the IoT (Internet of thing) concept ismore and more concerned by every citizen. It is not onlyused in a residential environment, but can also be utilized
for both agricultural and industrial application. The “IIoT”(Industrial Internet of thing) will also be proposed by thistrend. The concept of IIoT focus more and emphasizes
the communication of machine to machine, and machine
to user, so interface between the facility’s sensor is thekey point of this concept [1],[2].
The connection between the machines always uses thephysical wire in the traditional way. However, the defectis the signal type and transmission way might be limitedby the distance [3]. It also causes the system couldn’tchange the transmission dynamically at times when theemergency events occur. [4] also uses the MCU (MicroControl Unit) which carry the RTOS(Real-time operatingsystem) to collect multiple sensors data in the industrialenvironments. n this paper, the wireless connection isconcerned to replace the physical wire between themachine tomachine. Although the analog signal modulation has
been used for a long while, [5] mentions that digitalmodulation has advantage of better noise immunity,
Corresponding author’s E-mail: ccsong@nfu.edu.tw

2. System Architecture
The main goal of the system architecture proposed inthis paper is focused on wireless communication andcontinuous signal processing. In terms of microcontroller
selection, Texas Instruments' LAUNCHXL-CC1310 andRenesas' RX231 is used for system implementation. The71

radio modulation method of CC1310 is common
FSK/GFSK, and supports multiple frequency-shift
keying (MFSK) modulation. The RX231 MCU is mainly
used for data buffering and analog-to-digital conversion
which the maximum operating frequency is 54 MHz. The
peripheral parts support 4-channel DMAC (DirectMemory Access Controller), which can reduce the many
input/output interrupts and data transfer tasks for MCUloading.

Table 2. System wireless communication specification
RF Specification

Fig. 1 shows the proposed system architecture in thispaper. It consists of two MCUs. These two MCUs not
only response for digital data transformation, the mostimportant thing is to fulfill the wireless communication.
Due to the setting in this paper is the unidirectionaltransmission, the following section is divide into twoparts with transmitter and receiver to introduce in detail.

Bandwidth
Latency

24 kHz20.24 msRange

5m

Transmission power

14 dB

2.3 Receiver
The receiver has the same design with the transmitter.
In addition to enabling a timer to turn on the RF reception
within a fixed period. The parallel transmission is used tosend the digital data from the receiver to the external
DAC (digital-analog converter). By the repeatedly
receiving and converting, the analog output signal will
last continuous conversion.

Table 1. System specification table
System Specification
150 kS/s
12-bits

8-MFSK
4 MbpsIn the transmitter, the MCU enables a timer to trigger
ADC (analog-digital converter) to sample the analog
signal. When the sampling amount reaches the goal of RF(radio frequency) packet length, the MCU will turn theRF transmission on to transmit the whole packet to thereceiver. Since the hardware blocks of RF and ADC areindependent on the MCU. When the MCU performs a RFtransmission, the ADC can also keep sampling to thesignal, so that the data never lost.

Although this study is aimed at the transmission ofanalog signals, the digital signal transmission is also
added in the system to be more flexible and closer topractical applications. All the important settings arecarefully considered in the system specifications, whichmainly include system timing planning, communicationtransmission specifications, packet length, sampling rate,
and throughput.
Under the goal of the highest transmission rate and thelowest delay, the feasibility of the respective conditions
is evaluated and verified by the specific experiments toachieve the highest transmission rate under this systemarchitecture. The overall specifications of proposedsystem and wireless communication are shown in Table
1 and Table 2.

Sampling rate
Resolution

Modulation
Transmission rate

2.2 Transmitter

2.1 System Specifications

4-ch analog channel, 8-bits digital channel

915 MHzIn this paper, the application scenarios are mostlyinternal signal transmission in large-scale equipment orproduction line in factories. Therefore, in the system
specification, the transmission distance of up to about 5
meters can meet most transmission conditions. The
farthest transmission distance of the system will beverified in the section of experimental results. Although
the sub-1GHz frequency band transmission is applied inthis paper, the theoretical transmission distance can be
more longer, but because this study adopts 8FSK
modulation, compared with the common 2FSK, due tothe frequency deviation modulation characteristic so thatthe receiving sensitivity of 8FSK will be lower. It meansthat if you want to maintain the same transmission quality,
the relative transmission distance will be affected andshortened.

Fig. 1. The figure of system architecture

Channels

Frequency Carrier

2.4 Parallel Digital Analog Converter circuit
The DAC7821 IC is adopted in the DAC circuit, which
is produced by the Texas Instrument. The reason to use
the parallel transmission from MCU to the external DAC
circuit is the transfer speed. Due to the requirement forreal time convert of the analog signal, the serious
communication might cause further delay to the system
which is called the latency.

72

pin on MCU to indicate the moment from the first ADCtrigger. The interval to the first sinusoidal signal of theDAC conversion means the latency. The oscilloscopeshows the result which in the Fig. 3, the Ch4 (browncurve) is the input signal; Ch3 (light blue curve) is theresult of the DAC circuit output; and the two dotted lines
are used to mark the latency time by the rising edge (firsttrigger) in Ch1 and the first complete of DAC. It isobserved that from the first signal sampling to the DACconversion, the total latency takes about 9.56ms.

2.5 Active filter circuit
Due to that the system in this paper uses the digitalmodulation of wireless communication to transmit, theanalog signal data will be sampled to non-continuously
digital data. Because of the DAC performs the zeroorder hold for discrete-time signal, means that the data
will also become unsmooth caused by the reconstruction
on DAC. The active filter is designed to resolve thisproblem. The low pass active filter is implemented witha 4 order Butterworth filter. The goal expects that theanalog signal within the setting passband can be send
wirelessly and successfully and smoothly output results.
3. Experimental Results
In the experiment process, the function generator is used
to produce standard sinusoidal waveform. The MCU
samples this signal by a fixed period. The transmitter
sends the sampling data to the receiver by RF, then thereceiver can transmit the data to the DAC circuit. Afterthe conversions on DAC circuit, an oscilloscope is used
to observe and compare the output result of the active
filter circuit and the input source signal.

Fig. 3. The latency of input to output

3.3 Timer occupy by Hardware switching

3.1 The maximum Bandwidth of system

Due to hardware limitation of the MCU, when the CPU
is interrupted by RF receiver routine, the output pin can’t
be set. It causes the system can’t update the DAC output
in a fixed-length duration time. The reason is that themost of MCU never support hierarchy interrupt, when
receiver interrupt, output timer interrupt for DAC update
is disable.

The highest sampling rate of the ADC and DAC in thepaper is set on 160kS/s. The maximum passband width is
set in 16 kHz because the expectation of this paper is thatthe input signal to be at least consistent with 10 digital
data to be reconstructed.

Fig. 4. The situation of hardware switching

Fig. 2. The comparison of whole system output and input result

As shown in Fig. 4, the experiment is performed tomeasure this non-updating duration. In every 43.75us oftransmission frame, there is about 3.2 ms of non-working
interval.

In the oscilloscope waveform of Fig. 2, Ch4 (browncurve) is the waveform produced by the functiongenerator; Ch3 (light blue curve) is the output after DAC;
and Ch1 (indigo curve) is the result of the filter which isalso the signal after the reconstruction. The Fig. 2 showsthat the 16 kHz sinusoidal wave input signal can bereconstructed by 10 digital data.

3.4 Mixed frequency
The experiment is hoping that the system not justtransmits the data with fixed or single frequency, buttransmits the reality analog signal. Hence the experimentadds multi frequency to a signal in order to simulate it,and observe the result to know whether reconstruction is

3.2 Latency
The latency on the wireless communication isunavoidable. The experiment measures the effect of thelatency on the result. The experiment is used an IO output73

successful or not. This experiment also tests the filter
performance of its exact bandwidth.

5Frequency domain

x 10
4.5
4Amplitude

3.5

Fig. 5. The waveform data with 4kHz, 8kHz and 16kHz mixed
frequency sinusoidal wave

3X= 12000
Y= 230286.5178

2.5
2
1.5
10.5
0-1-0.5

0Frequency (hz)

0.5

15x 10Fig. 7. The frequency domain figure of output result

As mentioned above, due to the system only used MCUs
to fulfill the RF reception and multiple IO to transmit thesignal data, the reconstructed signal will have somevacant of signal in every transmission frame. The fixed
duration reduces the SNR. The related data is measured
as shown in Table 3, the lower effect to the lower
frequency signal. It also shows the lower signal will havebetter SNR.

Fig. 6. The DAC output and active filter result of 4kHz, 8kHz
and 16kHz mixed frequency sinusoidal waveFirst of all, the waveform of the mixed frequency form
4 kHz, 8 kHz and 16 kHz sinusoidal waveform is
produced as shown in Fig. 5. The Fig. 6 is measured fromthe output of DAC circuit. Ch3 (light blue curve) is theDAC output result and Ch1 (indigo curve) is the signal
after filter.
The red square in the Fig. 5 and Fig. 6 marks thedifference between the original signal and the signal afterfilter. From the result, it proves that within the 16 kHz
bandwidth, all of the signal can reconstruct to the original
signal successful.

Table 3. SNR of each signal input frequency

Input
SignalFreq.

Signal noise ratio
152.96dB
116.093dB
98.0937dB
68.1dB
62.6037dB
41.3466dB

1k
2k
4k
8k
10k
16k

3.6 System Bandwidth
In the general definition of circuit theory, the frequencyof signal strength within the attenuation peak of less than
-3dB is called “bandwidth.” In this paper, anotherimportant performance index is bandwidth. The two
conditions of bandwidth and effective bits are used toselect the appropriate transmission input frequency. In
the measurement experiment of system bandwidth, a sine
wave signal with a peak-to-peak value of 3.3 V is used as
the input signal. At this time, the frequency of the signal
generated by the signal generator is dynamically adjusted,
and the peak-to-peak output signal is observed withoscilloscope. The calculation of equation (2) shows that
under the input peak-to-peak sine wave signal of 3.3 V,
the voltage peak value of -3dB is about 2.33V.

3.5 Signal noise ratio (SNR)
SNR is defined as the ratio of signal power to the noise
power. Since the analog continuous signal is transmitted
wirelessly, the SNR is used to judge how much noise isin the output signal. In this paper, the measurement ofSNR is based on the frequency domain after the Fourier
Transform. Fig. 7 shows the spectrum of the signal
waveform. According to the frequency domain, calculate
the energy of input signal and the noise except for theinput signal. The last, the SNR can be calculated by (1),and it is effective evaluate the system.
𝐴𝐴𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠(1)
𝑆𝑆𝑆𝑆𝑆𝑆(𝑑𝑑𝑑𝑑) = 20 log10 ()𝐴𝐴𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛

1V𝑚𝑚 = 20log( ) ≈ -3dB√2(2)Therefore, the method of this experiment is to adjust thefrequency generated by the signal generator and observe
the peak-to-peak value of the output waveform in theoscilloscope. As shown in Figure 8, CH1 is the waveformgenerated by the measurement signal generator, and CH274

is the measurement system. For the output waveform, use
the function of the oscilloscope to measure the peak-topeak value. As shown in the red box in Fig. 8, when CH2
is 2.33 V, the current input frequency is a sine wave witha frequency of 24 kHz, so it can be determined The
system bandwidth proposed in this paper is 24 kHz.

5. Q. Gu, RF System Design of Transceivers for WirelessCommunications, 1st edn. (Springer, New York, 2005), pp.
67–77.
6. A. A. Ignatius, D. C. Samjay, R. Prathish and A. I. Rexy,Automated Monitoring of Industrial Loads Using Iot andControl Using Wireless Technology, Middle-East Journalof Scientific Research, 2016.
7. I. Müller, T. Companhoni, M. Götz, C. Protasio,Development of a Wireless Current Measurement Sensor
Node for IoT Applications, 2018 VIII Brazilian
Symposium on Computing Systems Engineering (SBESC),April 18, 2019.

Acknowledgements
This research was supported by the Ministry of Scienceand Technology, Taiwan, R.O.C. under Grant: MOST
107-2218-E-150-001 and 107-2218-E-150-007.
Authors Introduction

Fig. 8. Bandwidth measurement

4. Conclusion

Po-Yun ShihIn this paper, the digital modulation is used to conduct
the wireless communication. The system with digitalmodulation have the advantages of noise immunity anderror checking with error-control codes. Moreover, thetransmission power and transmission rate can be flexibly
adjusted in the digital modulation. As shown inexperimental results, that the proposed system could
effectively remove the equipment wiring in the industrialenvironment. Moreover, the system successfully issimulated and evaluated the situation of variety
frequency waveform in the industrial environment, andreconstruct the output signal to the original continuous
signal with a very low error. The system which
implements in this paper is proved that it can transmit thecontinuous analog signal by the wireless effective.
References

He received the M.S. degree in ElectricalEngineering
fromNational
YunlinUniversity of Science and Technology,Yunlin, Taiwan in 2020. His current researchinterests IoT Application.

Chung-Wen Hung

Chau-Chung Song1. S. S. A. Abbas and K. L. Priya, Self Configurations,
Optimization and Protection Scenarios with wirelesssensor networks in IIoT, 2019 International Conference on
Communication and Signal Processing (ICCSP), April 46, 2019.
2. Z. Bi, L. D. Xu and C. Wang, Internet of Things forenterprise systems of modern manufacturing, IEEE
Transactions on Industrial Informatics, January 16, 2014.
3. Q. Chi, H. Yan, C, Zhang, Z, Pang and L. D. Xu, A
reconfigurable smart sensor interface for industrial WSN
in IoT environment, IEEE Transactions on Industrial
Informatics, February 17, 2014.
4. S. Nuratch, A universal microcontroller circuit andfirmware design and implementation for IoT-based
realtime measurement and control applications, 2017
International Electrical Engineering Congress (iEECON),
October 23, 2017.

He received the Ph.D. degrees in ElectricalEngineering from National Taiwan
University in 2006. Currently he is anassociate professor in National Yunlin
University of Science & Technology. His
research interests include IoT, IIoT, PowerElectronics, Motor Control, AI Application.

He received the M.S. degree in Control
Engineering in 1994 and the Ph.D. degree inElectrical and Control Engineering from
National Chiao Tung University in 2001 atTaiwan. He is currently a distinguishedprofessor in Department of AeronauticalEngineering, National Formosa University. His researchinterests include the analysis and control of nonlinear systems
the integration application of networking information system,
the UAV technology, and the cloud network and CyberPhysical system (CPS).

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