Children Tracker - Senior Design Project Lab | ECE 445, Study Guides, Projects, Research of Electrical and Electronics Engineering

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CHILDREN TRACKER

By Man Yee Ho Wai Fong ECE 445, SENIOR DESIGN PROJECT SPRING 2006 TA: Ishaan Gupta May 1, 2006 Project No. 45 i

ABSTRACT

We designed a device called Children Tracker which uses radio frequency communication to track the location of a target in covered area such as supermarket or mall. Our project aimed to prevent children lost in such areas and helped parents to track their children’s location using this device. The system consists of two major units, one is holding by the children and the other is holding by the parents. All the units in our project are built with LINX RF modules. We use signal strength to determine the distances between antennae and the two units. By using triangulation in LabView, we locate the children with respect to the parents. Although we could locate the children’s position on computers, there are still improvements that information should be sent back to the parents unit which achieve the goal of our project. i

1. INTRODUCTION

Children tracker aims to prevent children lost in covered area such as supermarket or mall and help parents tracking their children using this device. We can always hear announcements broadcast from the help desk about parents looking for their children. No matter the parents find their children or not, it is bad enough for the parents worry about their children. Therefore, this project is worth to be done for reducing the fear of losing children. 1.1 Purpose The purpose of this project is to develop a network within a desired distance which is able to detect where the children are and report it to the parents. Different from the products currently out in the market, our goal is to provide a more precise location of the target. While most of the devices or services using Global Positioning System (GPS) can only determine the range where the target is in, our project gives the exact distance and direction of the target. Children Tracker is a low-cost and user-friendly system for the detection of children in covered areas. The final products are two handheld units with radio transmitters, receivers and LCD display. The display shows the direction in which the children is located relative to the parents and give the distance between them based on signal strength. Benefits to End Customer  Children will easily be tracked down under a covered area.  Parents do not worry about their children as much as before.  Avoid broadcasting announcement about children lost, causing disturbance to other customers. Product Features  Able to be use under covered area, while GPS does not work.  Using low frequency antenna to locate the units.  Using higher frequency antenna to transmit information in the desired distance.  Main computer control, can be able to display the units in the area  Information of the children unit will be displayed on the screen of the parent unit. 1.2 Specifications The project was split up to four parts (as shown in the Fig. A1 in Appendix A). They are the Children Unit, Parent Unit, Antenna Unit and Main Unit. The main unit should be able to calculate the location of the target unit. We used localization to determine the coordinate of the transmitters. To obtain the distance between the transmitters and the receivers, calibrations between the voltage level received from the RSSI pin and distance were needed. Then we can map the voltage level to distance (with respect to each receiver). We can now calculate the angle between the two receivers and the target unit using the following formula:

dr

d r d

i i j

cos

2 2 2

  ( 1 .1) From the angle and the distances obtained from the mapping above, we can calculate the exact coordinate of the target on the coordinate system we assigned. After all data was obtained, the main unit was able to compute the data bit which will be sent to the parent unit. 1.3 Subprojects 1.3.1 Children Unit The children unit needed to transmit a signal from the transmitter to the antennae constantly at 903MHz. 1.3.2 Parents Unit The parent unit needed to transmit a signal from the transmitter to the antennae constantly at 916MHz. It also needed to receive digital data from computer, interpreted it in microcontroller and displayed on LCD display. 1.3.3 Antenna Unit The antenna unit used to communicate with children and parents unit wirelessly. It needed to receive and distinguish signals from children and parents unit. In addition, it measured the signal strength of each unit for localization. Another function of the antenna unit was to transmit the digital data calculated in main unit to parents unit. 1.3.4 Main Unit The main unit did all the calculations to determine the distance between each transmitters and receivers and thus located the children and parents unit. It found the distance and angle of the children unit with respect to parents unit. With the numbers calculated, it interpreted the information into binary bit and sent it out to antenna unit.

For an operating frequency of 916 MHz, this yields LC = 4.715 X 10-17. From part shop, the smallest usable capacitor is 1 pF, and thus requires an inductor of 47 H to be used. After doing numerous calibrations on the RSSI pin to verify the accuracy, we preferred the LINX RF module to RLC circuit because the RF modules were in hand and we did not need to spend much time on implementing it. 2.1.3 Antenna Due to the unavailability of 315MHz and 433MHz transmitters and receivers, only 900MHz transmitters and receivers were used. The two channels we chose were 903MHz and 916MHz, thus antennae with center frequency of 916MHz were enough to receive signals from both channels. 2.1.4 Power Supply As mentioned above, microcontrollers were no longer used in our project; the receivers and transmitters were the only parts required power supply. A minimum of 2.8V and a maximum of 13V were required to operate the receivers and transmitters. For the transmitters on children and parents unit, we must use some handheld and long life battery. At first, we believed that two 3V alkaline coin cells connected in series would be our best option because its battery life is up to 10 years which were what we looking for. However, it provided only 0.4mA current which was not enough for operating the transmitters. Therefore, we changed to use a single EN-22 9V battery which provided a minimum of 25mA current to drive the transmitters. For the receivers on antenna unit, a power supply was being used to power up the receivers. Since the antenna unit needed to be on whenever someone needed to use the system to track their children, a long life power supply must be used. Also the antenna unit was fixed at certain location, the handheld battery were no longer required. As we did not want to change the battery so often, a power supply was the best option fulfilling all these requirements for antenna unit. As we did not finish the communication part between the antenna unit and the microcontroller, we did not make any battery decisions for this part. However, we knew that a maximum of 7.5V could be supply to the microcontroller. If we wanted to use the same 9V battery, a voltage regulator must be added to the circuit. 2.2 Design Description 2.2.1 Children Unit The children unit consists of a transmitter, an antenna and a battery, which is being carried by children. The final product of children unit is shown in Fig. B1 in Appendix B. The children unit is set to operate at 903MHz band by selecting channel 0, one of the 8 parallel selectable channels on the transmitter [2]. A 916MHz directional antenna is connected to the transmitter to communicate with the antenna unit. A 9V battery is connected to all Vcc in the transmitter. The schematic diagram is shown in Fig. C1 in Appendix C.

2.2.2 Parents Unit The parents unit is a unit carried by parents for tracking their children. It consists of a transmitter, an antenna, a microcontroller and a LED display. The final product of parent unit is shown in Fig. B2 in Appendix B. The parents unit is set to operate at 916MHz band for transmitting signal by selecting channel 5, one of the 8 parallel selectable channels on the transmitter. A 916MHz directional antenna is connected to the transmitter to communicate with the antenna unit. A 433MHz receiver is used to receive the digital data transmitted from the main unit. A 433MHz directional antenna is connected to the receiver to communicate with the antenna unit. A microcontroller processes the digital data received and interpreted them to useful information displayed on LCD display. A 9V battery is connected to all Vcc in the transmitter. The schematic diagram is shown in Fig. C2 in Appendix C. 2.2.3 Antenna Unit The antenna unit is a group of antennae connected to the main unit through wires so that they information will be sent to the main unit. There are four stations of antennae group placed at the four corners of the covered area. The final product of one of the antennae group is shown in Fig. B3 in Appendix B. Each antennae group consists of two receivers for receiving signals from children and parents unit separately. The receivers receiving signals from children unit is set to operate at 903MHz band by selecting channel 0, one of the 8 parallel selectable channels on the receivers. The receivers receiving signals from parents unit is set to operate at 916MHz band by selecting channel 5, one of the 8 parallel selectable channels on the receivers. A single 916MHz antenna is connected to both 903MHz and 916MHz band receivers. As suggested in the data sheet, a supply filter shown in Fig. 2 below is added to the circuit to provide a clean source of power to receivers. A 6V power from power supply is connected to all antennae groups. The schematic diagram of one of the antennae group is shown in Fig. C3 in Appendix C. Fig. 2 Supply Filter 2.2.4 Main Unit The main unit is a unit which connecting a computer to the antenna unit through wire to the NI- QAD board and obtain the signal strength using LabView. A block diagram built in LabView

Fig. 4 Diagram of Locating an Object Since not every location allows you to set up the antennae groups at the four corners of square described above, Fig. 5 shown below illustrates a more general case. 2.3.1 Calculations of the Coordinates of the Portable Units Given that we know the distance between antennae, to find the angle as shown in Fig. 5, we can use the following formula:

dr

d r d

i i j

cos

2 2 2

  where rij^ is the distance between antenna i and antenna j, di^ and dj is the distance between antenna i and antenna j and the portable unit (either children or parents unit) respectively. Fig. 5 General Coordinates between Antenna and Units For the value of di^ , we will calibrate the relationship between the voltage and distance. According signal strength of the antenna i measured, we try to get the distance from the graph shown in Fig. 6:

Fig. 6 Calibration of the relation between RSSI and the distance 2.3.2 Calculations of Distance between the two units

Let  xc^ , yc^  be the coordinate of the children unit,  x^ p , y^ p be the coordinate of the parents unit,

the distance between them is:    

2 2 d  x c  xp  yc  yp 2.3.3 Calculations of Angle between the Two Units Once we have the distances and angles (with respect to the antennas) we can assign the coordinate to the units. Depend on the location of the children unit; the main unit is able to determine the direction where the child is located with respect to the parents unit. The main unit will check the coordinate of both the units using Table. 1: AND xp > xc xp = xc xp < xc yp < yc NW N NE yp = yc W Found!! E yp > yc SW S SE Table. 1 Direction Determination The angle between them is: tan 1 p^ c p c x x y y

 ^

From the theory, we should get -2 as the slope of each linear fit of the plot above. This may due to the signal strength was not strong enough. We tried to solve this issue in two ways: Firstly, we tried to amplify the signal strength by adding the RF amplifier to the transmitter circuit. The amplifier did not amplify the strength but reduce it. As a result, we gave up this idea and proceeded to the next method. Secondly, we tried to use the RLC circuit as we designed before, but it did not help much for amplifying the signal strength. 3.4 Main Unit After the main unit received the signal strength from the RSSI pin, the main unit should be able to calculate the results, which are the coordinate of the parents unit, children unit and the direction of the children unit relative to the parent unit. All the results were observed on the LabVIEW. The main unit should also be able to generate the information signal. The signal generated from LabView was observed on the oscilloscope sampling at 1MHz, which is a square wave (representing the corresponding bit).

4. COST

4.1 Labor We estimated our future salary at around $ 4 0 per hour. The amount of time spent on working on this project was estimated around 20 hours/week, length of the project is 12 weeks. Using the following formula, labor cost is around $19, 200 Labor = 2($40/hour)(20hrs/week)14weeks = $ 22 , 400 4.2 Parts* Part # Description Qty Unit Price Price (>200) Unit Total Total (>200) Children Unit: TXM-900-HP3-PPO Transmitter 1 $29.45 $21.30 $29.45 $21. ANT-900-CW-QW Antenna 1 $5.48 $5.27 $5.48 $5. EN-22 9V Battery 1 $1.28 $1.28 $1.28 $1. 47μF CapacitorF Capacitor Capacitor 1 $0.66 $0.66 $0.66 $0. 0.1μF CapacitorF Capacitor Capacitor 1 $0.66 $0.66 $0.66 $0. Parents Unit: PIC16F877A Microcontroller 1 $5.15 $5.15 $5.15 $5. TXM-900-HP3-PPO Transmitter 1 $29.45 $21.30 $29.45 $21. RXM-433-LR Receiver 1 $13.56 9.63 $13.56 $9. ANT-433-SP Antenna 1 $0.67 0.48 $0.67 $0. ANT-900-CW-QW Antenna 1 $5.48 $5.27 $5.48 $5. BPI-216 LCD LCD Display 1 $55.00 $55.00 $55.00 $55. EN-22 9V Battery 1 $1.28 $1.28 $1.28 $1. 20 MHz Oscillator Oscillator 1 $0.57 $0.57 $0.57 $0. 47μF CapacitorF Capacitor Capacitor 1 $0.66 $0.66 $0.66 $0. 0.1μF CapacitorF Capacitor Capacitor 1 $0.66 $0.66 $0.66 $0. Antenna Unit: ANT-900-CW-QW Antenna 8 $5.48 $5.27 $43.84 $42. RXM-900-HP3- PPO Receiver 8 $45.15 $30.96 $361.20 $247. 47μF CapacitorF Capacitor Capacitor 4 $0.66 $0.66 $2.64 $2. 0.1μF CapacitorF Capacitor Capacitor 4 $0.66 $0.66 $2.64 $2. Total: $560.33 $424. Total Cost = Parts Cost + Labor Cost = $22,960.

Also, out project should aware of the privacy issues of the users. For multiple users operating the same device at the same time in the same area, our project should avoid any third party receiving information from other devices. Therefore, a caller ID must be added to increase the security issues. 5.4 Future Work There are more continuous of this project. Due to limited time, we could not finish the part for sending back information and display on the parents unit. This part should be completed in order for the parents to track the location of their children. Also, our system can only track one child at a time. Thus multiple channels should be added to the systems for tracking multiple children at one time.

APPENDIX A – OVERALL BLOCK DIAGRAM

Fig. A Overall Block Diagram

APPENDIX C – SCHEMATICS DIAGRAM

Fig. C1 Schematic Diagram of Children Unit Fig. C2 Schematic Diagram of Parents Unit

Fig. C3 Schematic Diagram of Antenna Unit