THE 8th INTERNATIONAL SYMPOSIUM ON ADVANCED TOPICS IN ELECTRICAL ENGINEERING May 23-25, 2013

Bucharest, Romania  

Hardware Design of a Street Lighting Control System with Vehicle and Malfunction Detection

Lavric Alexandru, Popa Valentin Stefan cel Mare University, Computers, Electronics and Automation Department, Suceava, Romania

lavric@eed.usv.ro

Abstract—This paper presents the hardware development of a street lighting monitoring and control system. The system consists of the JN5148 wireless transceiver, the dimming circuit that uses a PWM (Pulse Width Modulation) signal, the vehicle detection circuit and the circuit for detecting potential malfunctions. One way to achieve vehicle detection is the integration of a PIR sensor (Passive Infrared Sensor) into the system. Another way to detect vehicles is the integration of a sensor that uses the Doppler effect. The results obtained show that the Doppler sensor helps reduce false alarms detected by the PIR sensor, having immunity to temperature variations in the operating environment and a greater detection range of over 20m. Another aspect that has been analyzed is the circuit for the detection of possible malfunctions that are reported to the control center, thereby helping to reduce maintenance costs.

Keywords: Doppler sensor, malfunction detection circuit, monitoring system, street lighting control, vehicle detection

I. INTRODUCTION

The reduction of energy consumption is rather a topical problem [1]. Some related papers present and analyze the various aspects of the street lighting monitoring and control systems [1] - [5].

One of the papers [1] presents a proposal of an original architecture for street lighting control. The main advantages of this system consist in the significant reduction of the electricity consumption costs and of the maintenance costs by reducing light intensity (dimming).

The system architecture is based on a WSN (Wireless Sensor Network) sensor network which operates using the Jennet communication protocol [1]. Technological progress has led to the implementation of new technologies and street lighting control systems, which replace the classical systems, thus facilitating power saving, maintenance and improving the lighting quality. In [2] is presented a comparative analysis of the LED and HID (High Intensity Discharge) technologies and of the control systems that can be integrated into modern street lighting systems.

In a related work [3], is presented the software development of the street lighting monitoring and control system. The system includes a vehicle detection algorithm that entails the adjustment of light intensity (dimming) depending on the presence of vehicles, the system thus contributing to the further reduction of power consumption. Thus, when a vehicle is detected, the node automatically turns the lamps on to a light intensity that can be set by the user.

In [4] we have presented the development of a traffic prediction algorithm which can be integrated into the street lighting control system. The hardware development of the street lighting monitoring and control system is presented in this paper.

II. THE WSN NODE

The JN5148 [6] which is a low cost transceiver, is used in the hardware implementation. The communication protocol used in the WSN network is the JenNet, which is based on the IEEE 802.15.4 standard that meets the requirements in terms of high performance, such as: the possibility of integrating a large number of nodes, reduced complexity in developing applications, and lack of additional license costs.

The JenNet communication protocol enables the integration of a large number of nodes, up to 2000, for a single coordinator and, implicitly, a gateway [7]. Thus, the novelty of this system consists in the possibility of integrating a large number of nodes, the dimming of the light intensity depending on vehicle detection and the reporting of the malfunctioning lamps to the control center.

Fig. 1 shows the internal structure of the JN5148 transceiver, which integrates two 12-bit analog-digital converters (ADC), two 2-bit digital-analog converters (DAC), an SPI (Serial Peripheral Interface) interface and UART (Universal Asynchronous Receiver/Transmitter) [6].

Fig. 1. Internal structure of the JN5148 transceiver and the system functions.

The timer is used for designing a clock that would enable the on/off controls according to a flexible schedule set in advance by the user. The ADC converters are used to retrieve information from the sensors and the DAC is used for generating the PWM signal used for reducing the light intensity. The UART communication interface is used for communicating with the computer unit installed at the

978-1-4673-5980-1/13/$31.00 ©2013 IEEE

command center of the street lighting monitoring and control system.

III. THE DIMMING CIRCUIT

The dimming method used in the system is the digital PWM method which provides certain advantages over the analog method [2]. The driver integrated in the LED street lighting lamp can be controlled to perform the dimming process via a 10V PWM signal. Since the PWM amplitude coming from the JN5148 is about 2.8 V, a particular circuit converts it to 10V amplitude, as shown in Fig. 2.

Fig. 2. The PWM circuit.

Fig. 3 presents the PWM signal received from the microcontroller, which is used for a 25% dimming, a peak-to-peak voltage of 2.6 V and a frequency of 156 Hz. The time interval during which the lamp is on is about 1.59 ms in a time period of 6.4 ms.

Fig. 3. The PWM signal from the microcontroller (Duty Cycle 25%).

IV. VEHICLE DETECTION

A. The PIR sensor The street lighting monitoring and control system is able to

adjust the light intensity depending on the presence of vehicles. One way to achieve detection within the system is the integration of a PIR (Passive Infrared Sensor) sensor. The PIR sensor reacts to changes in the infrared thermal radiation flow. Fig. 4 shows the PIR sensor of the DSC LC-100PI type [8].

The sensor consists of a series of lenses that collect the light from the infrared spectrum and send it to the processing circuit that converts it into energy. The processing circuit determines if a detection occurs. Movement is detected when a body with a certain temperature passes by the infrared source. Table I presents the advantages and disadvantages.

Fig. 4. Structure of the PIR sensor.

TABLE I PIR ADVANTAGES/ DISADVANTAGES

Advantages Disadvantages • Uses the QLIT (Quad Linear Imaging Technology) technology that improves the analysis of the detected bodies [7] • Surveillance range 15m x 15m • Detection angle opening 900 • Immunity to small animals (maximum 25Kg) • Automatic temperature compensation • Adjustable PIR sensor sensitivity • Protection from electromagnetic interference and radio frequency (30V/m, 10-1000MHz) [7] • Protection against vandalism • Power consumption 8.2-16V • Standby consumption: 8mA (± 5%) in active mode: 10mA (± 5%) • Reduced costs

• Sensitivity to sudden temperature changes in the environment. • Activation time 60sec (± 5sec) • Sensitivity to direct sunlight exposure. • Detection range 15 m • Detection time 2 sec (± 0.5sec) • False alarms

Thus, the use of the PIR sensor for vehicle detection has a number of disadvantages related to the environment in which it operates, as it is exposed to direct sunlight, which causes large temperature differences and generates false alarms that can compromise the entire street lighting control system. Moreover, the detection is limited to 15m in ideal operating conditions (distance may decrease down to 5m in actual operating conditions).

B. The Doppler sensor Another way to achieve vehicle detection is the integration

of a sensor that uses the Doppler Effect. The sensor sends an electromagnetic (EM) signal to an object and receives back a signal reflected from that particular object. By monitoring the delay between the signal transmission and the reception of the reflected signal, the distance to the object can be determined. If the object is moving, the frequency of the received signal will be translated from the frequency of the sent signal to another frequency, and this effect is known as the Doppler Effect [9], [10]. The translation of the Doppler frequency is determined by the radial velocity of a moving object in the LoS (Line of Sight) direction. The sensor can measure the radial velocity of a moving object, based on the changing Doppler frequency of

the received signal. The Doppler frequency shift is usually measured in the frequency area by means of the Fourier transformation of the received signal. In the Fourier spectrum, the maximum component is the Doppler frequency induced by the radial velocity of the direction of movement of the object. The Doppler frequency bandwidth is an estimate of the movement velocity through the micro-Doppler effect. The frequency of the transmitted signal should be as stable as possible in order to achieve the proper monitoring of the received signal status.

Fig. 5 presents the Doppler GH100 [11] sensor that has been tested for vehicle detection in the street lighting monitoring and control system. The sensor includes two antennas used for signal transmission (Tx), two antennas for receiving the reflected signal (Rx) an oscillator that generates the signal and a mixer circuit.

a) external structure b) internal structure

Fig. 5. The Doppler GH100 sensor.

The sensor operates on the 10.525GHz frequency in the X band, with a maximum power of 14dBm and a supply voltage of 5V. The maximum current is of 60mA maximum, the harmonic emissions are of -10dBm, the sensitivity amounts to -86dBm, and the antenna gain being of 8dBi [11].

The advantages of the Doppler sensor as shown by the obtained results are: reduced false alarms, immunity to temperature changes in the operating environment, detection distance of over 20m, possibility to determine the moving speed of an object, almost instantaneous activation time, immunity to direct sunlight exposure and a detection time of 50ms. By integrating the Doppler sensor in the street lighting control system the false detection problem of the PIR sensor is solved.

Since the amplitude of the sensor signal at the IF output is very small (by the order of millivolts) the signal has to be processed and applied to the terminals of an amplifying circuit designed by using the LM1324 operational amplifiers, as shown in Fig. 6. When an object moves in the radial direction of the sensor, at a speed of 1 m/s, the IF output frequency is of 40Hz/s. The amplitude of the output signal is directly proportional to the distance from the object.

The input signal amplitude is of 4V and its connection to the ADC convertor terminals of the JN5148 module will require a voltage divider that reduces it to a voltage of 2 V. The maximum signal amplitude that can be applied to one of the two ADC converters is 2.4V. When no vehicle is detected, the recorded ADC value ranges between 1152-1400 mV.

Fig. 6. The Doppler GH100 sensor circuit.

Table II shows the values recorded by the ADC when a vehicle is detected at various speeds.

TABLE II ADC VALUES DOPPLER SENSOR

Distance (m)

ADC value (mV)

1m 2000 3m 1956 5m 1912 7m 1868 9m 1982

11m 1604 Thus, when the presence of a vehicle is detected, the value

recorded by the ADC exceeds the 1400 mV threshold.

V. MALFUNCTION DETECTION CIRCUIT

The street lighting control system must be able to detect any malfunctions that may occur due to any lamp that does not work within normal parameters, without any need for on-site inspection or passer-by notifications. These malfunctions are reported to the command center. Thus, an ACS714 [12] current sensor manufactured by Allegro is used. The ACS714 is a cost efficient alternative for current measurement.

The sensor incorporates a Hall low-offset linear sensor circuit. When a consumer is applied, the current generates an electromagnetic field that is transformed by the Hall circuit into a directly proportional voltage. The sensor output is a voltage that is directly proportional to the voltage identified by the consumer. The sensor resolution is of 66mV/A. Fig. 7a presents the block diagram of the ACS714 sensor. The supply voltage is of 5 V, just as the voltage of the Doppler sensor used for vehicle detection. The signal generated at the sensor output signal is set at 2.4 V. As seen in Fig. 7, a resistive divider (R1, R2) is used for reducing the output voltage to 2V, since the ADC input of the JN5148 module has a maximum voltage of 2.4 V. The speed of a vehicle can be calculated using (1) approximation, where c is the speed of light, f is the direct signal frequency and fIF the Doppler frequency.

Fig. 7b presents the ACS714 sensor incorporated in the street lighting monitoring and control system, connected to the terminals of a LED lamp of 60 W.

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v =c2 f

fIF ≈ 0.0237 ⋅ fIF

(1)

a) internal structure b) system integration

Fig. 7. Structure of the ACS714 sensor.

Table III shows the values recorded by the ADC converter for the different dimming levels.

TABLE III

ADC VALUES ACS714 SENSOR

Dimming ADC value (mV) 0% 2080

25% 2085 50% 2090 75% 2095

100% 2100

Fig. 8a presents the lighting control system that includes the command module, the 60 W Led Electromax lamp, the Doppler sensor, the ACS 714 sensor and the oscilloscope used. Fig. 8b shows the PCB of the Doppler sensor circuit, the ACS and the one used for acquiring the PWM signal.

a) Street lighting control system b) PCB- sensors

Fig. 8. The street lighting control system configuration.

VI. CONCLUSIONS

This paper presents the hardware development of the street lighting monitoring and control system. One way to detect movement is to integrate a PIR (Passive Infrared Sensor) within the system. The employment of the PIR sensor for

vehicle detection has a number of disadvantages due to the environment in which it will operate. Another way to detect vehicles consists in the integration of a sensor that uses the Doppler Effect. The obtained results show that the Doppler sensor helps reduce the false alarms detected by the PIR sensor, it is immune to temperature changes in the operating environment, and has a greater detection range amounting to over 20m.

Another aspect under consideration was the circuit for the detection of possible malfunctions which are reported to the command center and thus reduce the maintenance costs related to the street lighting system. The circuit entails the integration of an ACS714 Hall translation circuit. The main advantages of this system consist in the significant reduction of the electricity consumption costs and of the maintenance costs, by reducing the light intensity (dimming) after processing the information received from the sensors, such as: light level monitoring and vehicle detection. The automatically generated reports enable the monitoring of heavy traffic areas and help determine effective measures to optimize road traffic.

ACKNOWLEDGMENT

This paper was supported by the project "Improvement of the doctoral studies quality in engineering science for development of the knowledge based society-QDOC” contract no. POSDRU/107/1.5/S/78534, project co-funded by the European Social Fund through the Sectorial Operational Program Human Resources 2007-2013.

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[3] A. Lavric, V. Popa, I. Finis, C. Males, „Performance evaluation of Tree and Mesh ZigBee Network Topologies used in Street Lighting Control Systems,” Przeglad Elektrotechniczny, pp. 168-171, 2013.

[4] A. Lavric, V. Popa, „A Traffic Prediction Algorithm for Street Lighting Control Efficiency”, JACS Journal, in press.

[5] M. Ziane, K. Medles, M. Adjoudj, F. Miloua, J.J. Damelincourt, A. Tilmatine, "Modelling the Dynamic Interaction Power System Lamp Application to High Pressure Mercury Gas Discharge Lamps," Advances in Electrical and Computer Engineering, vol. 7, no. 2, pp. 49-54, 2007.

[6] http://www.jennic.com/products/wireless_microcontrollers/jn5148 [7] http://www.jennic.com/products/protocol_stacks/jennet [8] http://www.kosmodrom.com.ua/data/DSC-LC100PI.pdf [9] F. Chatzigeorgiadis, and D. Jenn, “A MATLAB Physical-Optics RCS

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[11] ”Datasheet GH100” http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/GH100Datasheet.pdf

[12] ”DataSheet ACS714” http://www.pololu.com/file/0J196/ACS714-Datasheet.pdf