Senior Design Project - Final Report

The "Child Monitoring Device" (CMD) is a device specifically designed for a parent to supervise his/her child’s activities. This device is a system that includes a Tracer/Monitor and a Communication Dummy. It will be designed for use in the home as well as for outside of the house. The parent will be able to monitor the distance and position of the child within a certain radius without any direct supervision. The device will also have a buzzer that alerts the parent whenever the child is in contact with water (i.e. a swimming pool or bathtub) or beyond a specified distance from the parent. Technically, this device uses radio frequency waves to send and receive signals from the device worn by the child to the parent’s monitor.

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PROBLEM STATEMENT

Children around the age of 5 tend to be very active. They are curious about things that take place around them and will venture off without any warning. It is not always easy for parents of guardians to take care of their children every second. Consequently, children may be involved in accidents that our device will help avoid. Parents need some sort of device that would assist them in looking after their children. Our senior design project called the "Child Monitoring Device" (CMD) is the solution to this dilemma. By using this device, parents will be able to monitor the location of their child and see if he/she is near water without having to accompany them all of the time.

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DESIGN OBJECTIVE

Generally, the "Child Monitoring Device" consists of two components, a Tracer / Monitor (used by the parents) and a Communication Dummy (attached to the child).

In order to initiate communication, the Tracer sends out a radio signal periodically to the Communication Dummy. As the Communication Dummy receives the signal, it will transmit another radio signal back to the Tracer. A micro-controller is embedded in the Tracer, which controls the signal generator and will compute the distance the child is from the parent. The Tracer is also equipped with a position sensor that monitors the location of the child.

In addition to just sending a signal back to the Tracer, the Communication Dummy has a special sensor that will trigger whenever the child is in contact with water or is not within a specified radius. When this happens. The Communication Dummy will activate the signal generator and transmit a radio signal to the Tracer to report the situation. Having a buzzer attached, the Tracer will assert a command that triggers a buzzer notifying the parents that the child could be in trouble.

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ASSUMPTIONS AND LIMITATIONS

In developing the child monitoring device our team made assumptions about how the device will be used and what preferences the user will have. The following details those assumptions as well as the limitations that arose in developing our device.

ASSUMPTIONS................................................................................................ Before the device could be designed several assumptions had to be made. First we established that our device would not be any sort of substitute for watching children, but would be an aid in avoiding accidents. This is an important point that the team wanted to make sure that there was never an idea that it could replace adult supervision. Another assumption made was that the device would be directed toward 4 to 8 year olds. The age group was important in determining the distance that the device is able to cover. One final assumption that needed to be made before the team could start the design was that the device must be portable and affordable.

Throughout the design and testing of the Child Monitoring Device the team had to make several more assumptions about the device. One of the major decisions the team had to make involved the direction sensor. After determining that displaying on the screen the direction of the child would be impractical, the team determined that an audio alarm would suffice for the functions that would have came from the direction sensor. The team also assumed that the child device was going to have to be durable. Considering the age group which will be using the device, this is an easy assumption to make. Another item assumed was that the parents will be responsible enough to turn off all power when the Child Monitoring Device is not in use. Building any feature that would turn the power off automatically would both complicate the design and also could be dangerous if the device were to turn itself off at the wrong time.

LIMITATIONS..................................................................................................... The Child Monitoring Device’s limitations can be separated into two categories: financial and time/knowledge.

Financial........................................................................................................... The financial limitations of our budget played a large role in determining the equipment we would use for our prototype. The HC-11 processor is much larger and more sophisticated than what is needed for our device. Given the alternative of purchasing a totally new processor for or testing the HC-11 sufficed. Another limitation was in the transmitters and receivers. In the manufactured device the frequency of the transmissions would be much more near 900 MHz. For our testing the 300 MHz transmitters worked just fine. Also because of the low bandwidth the Child Monitoring Device needs, simpler encoders/decoders can be built. Although price limited the components of our device in our prototype, low costs in manufacturing in mass quantities would keep the device affordable.

Time/Knowledge................................................................................................ The limitations of time/knowledge were basically related to the direction sensor. Each team member spent many hours researching ways to implement this device. Although a couple theories were suggested both of them were highly theoretical and advanced. The determination that the team would not be able to solve this dilemma in any determining factor along with comments from parents who felt that they would not use that feature led us to eliminate the direction sensor from our device.

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TECHNICAL APPROACH

The technical solution for the child monitoring device is separated into three parts: components, functions, and possible alternatives. These sections define what parts comprise to make the device, how each function works and also gives some of the teams rejected ideas respectively. Click here to see the schematic of the CMD.

COMPONENTS

MC68HC11 Microcontroller................................................................................. The MC68HC11 is a very good low power microcontroller that provides an on chip serial interface. The serial interface makes it easy for the other devices to communicate with the microcontroller. Also available with the MC68HC11 is an easy interface with a display screen, which are both available for use through Iowa State University. The Monitor.c program (Click here to see the code) is downloaded serially to the memory on the controller board.

* This is actually much more powerful than the child monitoring device would ever use but it's availability and the team's experience with using it made the MC68HC11 the best option.

MC68HC11

TX-66(99) / RE-66(99) Transmitters and Receivers.............................................. The child monitoring device uses two sets of transmitters and receivers. The TX-99 transmitter is on the parent's device and transmits a 310 MHz signal to the RE-99 receiver on the child's device. Also on the child's device is a TX-66 transmitter which transmits a 300 MHz signal to the RE-66 receiver located on the parent’s device. The signal transmitted is sent out serially as instructed from the encoder.

TX-99 Transmitter

RE-99 Receiver

TX-01 Encoder / RE-01 Decoder.......................................................................... The encoder and decoder are devices that the team did not plan on using at first, but quickly learned that they would be necessary for accurate communication. The TX-01 encoders and the RE-01 decoders work with both the 66 and the 99 models of transmitters / receivers.

The TX-01 encoder's purpose is to take 12 parallel inputs and send these inputs out serially to the transmitter. Inputs 1-8 (Click here to see the schematic of the CMD) are used as addresses and can be set to high or low by switches on the TX-01. This address is used by the RE-01 decoder to identify the source of the signal. The remaining 4 inputs (9-12) are the data lines which can be connected to external devices.

The RE-01 decoder's purpose is just the opposite of the TX-01 encoder. It receives a signal serially and coverts it to a 12 bit parallel signal. It than check the first eight bits with the address settings on RE-01 and verifies that the signal is from the right TX-01 encoder. If the address check passes than bits 9-12 output the corresponding data to external devices.

TX-01 Encoder

RE-01 Decoder

* The other devices are standard switches, speakers and circuits.

FUNCTIONS........................................................................................................ The three major functions of the child monitoring device are the distance sensor, the pager, and the water sensor. These functions are described below.

Distance Sensor................................................................................................ Explaining how the distance sensor works is easiest by going through one distance calculation cycle. This cycle is repeated every 7 seconds, which updates the distance value (Click here to see the schematic of the CMD for clarification on the data lines).

1) The MC68HC11 sets the D1 on the parent's device high. Concurrently the timer in the MC68HC11 starts counting clock ticks.	Figure 1
2) The TX-01 encoder senses the change on D1 and sends the data to the TX-99 transmitter to be sent out serially.	Figure 2
3) The signal is than received by the child's device's RE-99 receiver which is than decoded by the RE-01 decoder and the new data is placed on D1.	Figure 3
4) The TX-01 encoder on the child's device senses the change on D1 and sends out the data to the TX-66 transmitter to be sent out.	Figure 4
5) The returned signal is received by the parent's device's RE-66 receiver, decoded by the RE-01 decoder and the data is placed on the D1 line.	Figure 5
6) When the MC68HC11 detects the new data on D1, it stops the internal timer, converts the clock ticks into distance, and then displays the results to the screen.	Figure 6

* The values on D1 are reset to low to prepare for the next transmission cycle.

Pager..................................................................................................................... The pager is a switch connected to the D2 line on the parent's device. When the switch is asserted, the change in data will cause the parent's device's TX-01 encoder to transmit the data. When the child's device's RE-01 decoder receives the new data, it will send out the data on the D2 line. This change will close the circuit and cause the buzzer to go off.

Water Sensor....................................................................................................... The water sensor itself is on the child's device and consists of two wires which are separated by 1 cm, one wire going to ground and the other connected to input data line D3 on the child's device's TX-01 encoder.

When a volume of water encompasses the two wire the circuit is closed and a high is placed on D3. This new data is transmitted to the parent's device's RE-01 decoder which places the data onto the D3 line. The D3 line is connected to a buzzer which is than activated, alerting the parents of the child's danger.

POSSIBLE ALTERNATIVES.................................................................................. In designing the device, several other alternatives to the current design were discussed but were tabled for several reasons.

Micro-controller - The HC11 was chosen over other micro-controllers for two main reasons:................................................................................................................. 1. Our team had experience working with the HC11.................................................. 2. It was available to us to use for free

Transmitters/Receivers - The team decided on the TX and RX models from Digitec because it seemed to fit our needs the best. The frequency was efficient enough and they came with adjustable address lines which made it easy for the to transmitters/receivers not to read the wrong signal.

Water Sensor- The team briefly pondered using a fancier device but experiments quickly showed that a simple open circuit would work just fine.

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END PRODUCT DESCRIPTION

The child monitoring device is able to communicate back and forth between the parent’s device and the child’s device. Below are the three main features that the product supports at this time.

Water Detection.......................................................................................... Within the range of 50 feet, this product able to sense water and assert a warning signal when the child is submerged in water.

Pager......................................................................................................... Parents will be able to use this product to page their child and find out his/her location. When a button is pushed on the parent’s device, an alarm will sound on the child’s device, which can be then used to locate the child.

Distance Calculation and Warning Inform...................................................... The distance calculation program can be used take the distance calculated and compare it to preset values to determine if it is out of the desired range. If it is out of range an alarm will sound alerting the parent. The calculated distance can than be displayed to the screen. The team was unable to get the transmitters and receivers to transmit at a consistent rate and therefore the child monitoring device is unable to calculate the distance accurately.

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EVALUATION OF PROJECT SUCCESS

Budget & Human Effort.................................................................................... The budget spent on this project was cheaper than expected. The costs of the water sensor and direction sensor–pager are cheaper in cost and design-hours than was predicted at the star of the project. The major reason was that the design of both the water sensor and the pager was less complicated than then what was expected. The time and money saved here let the team allocate more resources to other features, which improved efficiency.

Knowledge and Skills....................................................................................... One of the main goals of the design team was to collaborate the member’s strong computer knowledge and basic electronic skills into a positive project and learn how to use this knowledge as one team. All three team members learned how to efficiently work together. The team was able to develop a further understanding of radio frequencies, logic design, and circuit integration. But more than anything, the team feels their improved teamwork skills is a valuable ability that has and will prove to be very useful. With the team’s new knowledge in the electronic field, computer programming, and teamwork, we feel the development of this project had been a great experience.

Design

Water Sensor............................................................................................. The design and implementation of the water sensor was delayed; however, the human effort that was spent on the implementation was less than expected. So, this milestone is considered fully met.

Direction Sensor (Pager)............................................................................ The team replaced the direction display feature with the pager. The pager is less sophisticated but many parents felt that the audio alarm would be more useful. The pager is fully operational and the team considers this milestone fully achieved as well.

Distance Calculation............................................................................... The software, wiring, and output/input devices all are up and working correctly. The circuit communicates in a full circle but unfortunately signal interference from using two pairs of transmitters and receivers, provided enough disruption to eliminate any consistent time value. Although much time was put into solving this problem, ultimately the team decided that two transmitters with a much greater difference in transmitting frequencies would be necessary. This shows that, the team needs to spend more time and effort on this milestone and develop more knowledge in the field. So this milestone was not fully met.

Radio Signal, Micro-Controller Programming & LCD Display..................... The team was able to develop a fully operational circuit. Although the team was never able to consistently read the distance, the circuit is completed and communicates between devices. The team was able to make the necessary parallel to serial and serial to parallel transitions. This was a big question for the team at the beginning of the product so the team feels that getting that feature working is a success.

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TESTING

Phase 1 - Transceivers........................................................................................ To ensure the two transceivers were functioning, each of the transceivers were tested separately. This was to make certain that the receiver was able to receive signals generated by its corresponding transmitter by configuring identical address bits to the decoder and encoder. At this stage, different data bits were sent out from the encoder to the decoder to get the desired results.

At the next stage, the two transceivers were tested simultaneously. This stage is somewhat similar to the previous stage. One transceiver was defined to be part of the parent’s monitor and the other to be part of the child’s device. First, the child’s device had to receive the signal from a particular data line(s) that was transmitted by the parent’s monitor. Once the decoder on the child’s device verified the signal and the data line(s), the child’s device was then tested to see that it transmitted a signal back to the parent’s monitor. Finally, the decoder of the parent’s monitor had to verify that signal. This was to make sure that the parent’s monitor was able to get back the desired signal it sent out and the data line(s) it asserted at the beginning of transmission (Signal Loop).

This phase was a very important step in testing Phase 4. After completing Phase 1 successfully, the team went on to the next phase of testing.

Phase 2 – Water Sensor..................................................................................... An open circuit was assembled using one of the data lines available on the child’s device (on the encoder board). When this data line was grounded by using water as a conductivity medium, a short circuit should take place. The team had to test to see if the parent’s monitor received a high data signal. Once the team was sure the signal was being transferred correctly they tested the buzzer to make sure it sounded appropriately when the child’s device contacted water.

Phase 3 – Parent-to-Child Pager........................................................................ An open circuit was assembled using one of the data lines available on the parent’s monitor (on the encoder board). When this data line was grounded by using a debounced-switch (pager button), the data line was tested on child’s device to ensure there was a short circuit. This condition being satisfied, the speaker than had to be tested to make sure it would activate when the switch was pressed and it would stay on until the parent pushed the button again.

Phase 4 – Distance Sensor............................................................................... Once Phase 1 was completed, than much of the testing needed for Phase 4 was complete. Using the counter to fetch the time it takes for the signal to travel from and back to the parent’s monitor, the HC11 will process the time and display the distance to the screen. The software was tested by inputting set values directly to the HC11.

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FUTURE WORK

There are several items for which could be worked on for the Child Monitoring Device.

One feature that could be added is for the ability of one parent's monitor to be able to monitor multiple number of children. This feature would make the child monitoring device much more useful for the parents of who have more than one child that they are responsible for looking after.

Another possible improvement is looking into the possibility of tracking the child’s device through the cell phone network. This way if an emergency situation arose, the cell phone companies would be able to locate the child. This could also be achieved through global satellite positioning but as of today the cell phone network would fit the power and size constraints much better than global satellite positioning does.

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FINAL BUDGET

Tasks/Phases		Planned Effort (Person Hours)	Actual Effort (Person Hours)	Planned Cost ($)	Actual Cost ($)
Meeting with Advisor		40	30	0.00	0.00
Updating Web Page		30	25	0.00	0.00
Research		50	60	0.00	0.00
Project Plan		15	20	0.00	0.00
Project Poster		30	40	50.00	60.42
Design Review		15	12	0.00	0.00
Oral Presentation		10	10	0.00	0.00
Design Transceiver	Transmitter (TX-66)	5	5	10.00	18.40
	Receiver (RE-66)	5	5	10.00	11.68
	Transmitter (TX-99)	5	20	10.00	10.00
	Receiver (RE-99)	5	15	2 x 10.00	2 x 11.68
	Encoder (TX-01)	5	20	2 x 20.00	2 x 16.72
	Decoder (RE-01)	5	5	20.00	25.12
Design Pager/Direction Sensor		50	55	25.00	0.00
Program Micro-Controller		100	30	15.00	0.00
Design Monitor Display		20	10	20.00	0.00
Design Water Sensor		30	10	15.00	0.00
Testing and Debugging		50	90	10.00	0.00
Final Report		30	30	10.00	0.00
Final Oral Presentation		20	20	5.00	0.00
TOTAL		550	512	$ 260.00	$ 195.86

* 0.00 : funded by the university

As can be seen from the table, the process of designing the transceivers exceeded $100. This is because, the project requires a pair of transceivers, one for the parent’s monitor, and the other for the child’s device. The actual cost of the transceivers was $135.44, which is in fact very close to the planned cost of $120.00.

The availability of many of the University’s supplies cut down the total cost to $195.86 as compared to the planned cost of $260.00

The team saved many hours on the whole project due to both good teamwork and the changes made to our direction sensor as describe under the Assumptions and Limitations section.

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SUMMARY AND CONCLUSION

The experience and knowledge the child monitoring device team acquired throughout the entire senior design project is valuable in more ways than one. The team members did gain technical knowledge but the other lessons learned are greatly helping the members prepare for the transition from the classroom to the work force.

One of the big skills employers are looking for is communication skills. The experience of working in the team environment for a couple semesters really taught the members of the team how to communicate much more efficiently. The team was accomplishing more work in much less time at the end of the project then the team was at the start.

The team is also more experienced now in looking at and researching problems to see if there is a more reasonable approach than what the team first had in mind.

To conclude, the team members feel that the device produced, although not 100% operational in all functions, shows what can be done with an idea, teamwork, time and little patience.

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Send your comments to cmd-team@iastate.edu