Circuit Design And Construction Computer Science Essay

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The process flow of the electronic system for the Child care system was shown in Figure 4.1. The process started from the digital compass sensor, which give the direction of the target, next is the Xbee wireless module, the preset Xbee wireless module will start establish the connection to his pair devices. The Main controller which is the central processing of this system, it will send a data packet out through the Xbee to it pair device to get the time delay to reach the end device or can direct measure the signal strength form the RSSI pin from the Xbee to the microcontroller PWM pin. The raw RSSI value obtained is needed to do the EAL calculation before it converted the RSSI value to the unit distance. The LCD is for the display the information purpose and the last is the buzzer for the alert purpose if the pair unit in up to the preset range.

4.2 Microcontroller / Main Controller

A microcontroller (MCU) is a computer-on-a-chip and is a microprocessor emphasizing self-sufficiency and cost effectiveness, if compared with the personal computer processor or called general purpose microprocessor. The comparison of microprocessor and the microprocessor if both had three major parts which is Arithmetic Logic Unit (ALU), Control Unit and registers, but the difference the microprocessor and the microcontroller is the microcontroller has additional element like Read-Only Memory (ROM), Random-Access Memory (RAM).Normally microcontroller can easily found in embedded system like washing machine, oven and many more. Microcontroller also can divided into two type which is Reduced Instruction Set Computing (RISC) and Complex Instruction Set Computer (CISC) to make the clear between different this two type in by referring the instruction set ,CISC have a complex instruction while the RISC have a limited instruction only. The microcontroller can be programmed by using assembly language and C code. There are many type of microcontroller in the market for example Microchip PIC16F877a, Renesas R8C , Atmel Atmega 328 and many more.

4.2.1 Arduino Uno Rev3 (Atmega 328)

In this project author choose the Arduino Uno Rev3 as the microcontroller for his system. Arduino was an open source physical computing platform based on a simple Input/output (I/O) in a single Printed Circuit Board (PCB) and a development environment that implement the Processing or Wiring language. Arduino could be used to develop standalone interactive objects or could also be connected to the software on user computer example Image Processing software-Processing.

Arduino UNO Rev3 was able to selected the input power supply correctly whether it was powered up by the Universal Serial Bus (USB) or using an external power source. The operating voltage for this board is 5 V and 3.3V. Table 4.1 shown the specification of the Arduino UNO Rev3



Operating Voltage

3.3V and 5V

Input Voltage (recommended)


Input Voltage (limits)


Digital I/O Pins

14 (of which 6 provide PWM output)

Analog Input Pins


DC Current per I/O Pins


DC Current for 3.3V Pin


Flash Memory

32KB (of which 2KB used by bootloader)





Clock Speed


Table 4.1 Specification of Arduino UNO Rev 3 [10]

Figure 4.2 Arduino UNO Rev3 Main Board [11]

4.3 Xbee Series 2

Xbee Series 2 is Zigbee compliance device .In this project author used the Xbee XB24-Z7WIT-004 module from Digi company. The Xbee Series 2 modules allow user to create complex mesh networks based on the Xbee ZB ZigBee mesh firmware, it also allow a very reliable and simple communication between microcontroller, computers, systems, anything with a serial port point to point and multi point networks are supported. [12]

Zigbee is an open and global standard for wirelessly networked control and monitoring solution that are low power, cost effective and reliable. The Institute of Electrical and Electronic Engineers (IEEE) a professional association gave a standard code to Zigbee which is IEEE 802.15.4, compliant radios and operated at 2.4GHz unlicensed ISM band.[13]

ZigBee 802.15.14

Bluetooth 802.15.1




Application Focus

Monitoring control

Cable Replacement

Web, Video E-mail

WAN, Voice/Data

System Resource





Battery Life (Days)





Nodes Per Network





Bandwidth (Kbps)





Range (Meters)





Key Attributes

Reliable, Low Power, Cost Effective

Cost ,


Speed, Flexibility

Reach ,Quality

Table 4.2 Different between Zigbee ,Bluetooth and GPRS

Figure4.3 Xbee 2mW Wire Antenna -Series 2

Figure 4.3 shown the Xbee RF modem from Digi International, it is a wireless transceiver. The Xbee uses a fully implemented protocol for the data exchange or communications that provides needed for robust network communication in a wireless sensor network (WSN). The addressing, acknowledgment and retries feature help to ensure that the data is safe delivered to the intended node, in addition the Xbee also able use for monitoring and control of remote devices.

4.3.1 Zigbee Protocol Stack

Figure 4.4 Zigbee Stack Architecture

4.3.2 Xbee Communication Modes

The Xbee transceiver is support two mode in communication for sending and receiving data from the controller. The communication were AT mode and API (Application Programming Interface) mode. Both have their own advantages. AT Mode

AT mode, also as known called Transparent mode. It is settled by default from Digi International, in this mode the message data itself is sent to the module and received by the controller. Figure xx shown the protocol link between the two is transparent to the end user and it appears to be nearly direct serial link between to another node, this make the transmission and reception of serial data between two nodes much simpler. It primary used in point-to-point communication between two xbee. It required entering the destination address for multiple communications. In this project the RSSI can be obtain by send a AT command , ATDB. API Mode

4.3.3 Xbee Duties

4.3.4 Xbee Serial 2 Specification

4.3.5 Antenna Style

4.4 HMC 6352 Digital Compass [17]

Figure 4.4 Honeywell HMC 6352 Digital Compass

In this project on the input sensor gave the heading value to used read is the digital compass as shown in figure 4.4. Digital compass also as known as magnetic sensor which giving the Heading output value to microcontroller to read. This compass module is combined with two axis magneto resistive sensor with the required analog and digital support circuit, and algorithms for heading computation. The others feature for this sensor is it had a up to 20Hz selectable update rate, up to 0.5 degree heading resolution, simple I2C interface.

4.5 Battery

C:\Users\Chee Seng\Downloads\251514_BB_01_FB.EPS_1000.jpg

Figure 4.5 Energizer 9V Ni-MH battery

In this project the power source used is Energizer 9V Ni-MH battery as shown in Figure 4.5. Since the application for this project is not heavy duty, it only had microcontroller, LCD display, Xbee transceiver, and buzzer. The power provide by the 9V battery is good enough for this application. Another thing take in consider is the battery have to be portable, and the battery is easily available in the market to make user friendly. Rechargeable battery also had advantage in cost saving and environment friendly.

4.6 Arduino 2*16 LCD keypad Shield [18]

Figure 4.6 Arduino LCD keypad shield

LCD used in this project were displayed the data for RSSI and heading value. It made the fine tune process easier, and it give information to end user read when using. This LCD keypad shield as shown in Figure 4.6 is operated at 5V, others feature for this shield are is using arduino LCD 4 bit library, it is a 2*16 LCD. In additional it also have 6 push buttons for select, left, right, up, down and reset function depends how the programmer configure those buttons. The purpose author choose this LCD keypad shield is, it is plug and play when used in Arduino main board, and no soldering or fly wiring needed.

4.7 Buzzer

C:\Users\Chee Seng\Desktop\Thesis\buzzer.jpg

Figure 4.7 5V Buzzer

The used buzzer in this project is to emit sound to alert user. A small buzzer is choose because the device is near to the user so it is load enough to alert the user, it do no need over size the specification, make the size of the device smaller and more power saving.

4.8 Circuit Construction [8] [15]

A good circuit will give a better output result. Xbee work in high frequency which is 2.4Ghz~2.4835Ghz, at this frequency the noise between Xbee and others components is easily occur although the noise can reduced by the RC filter but the noise in the connection between the Xbee and microcontroller might affect the desire performance. Hence reduce the noise author solve the problem using design a PCB board .which is all the connection is place on the board at direct connect with microcontroller. Although the board can obtain in market, for learning process and early stage functional tested a simple PCB is designed. There were two methods to get the PCB done which was through the etching process or through the drilling machine. In this project author was select the etching process due to used lesser time and least complicated compare to using drilling machine.

4.8.1 PCB Construction Criteria [8]

From the Xbee Arduino Shield it PCB is a double layer board but for the study purpose the author designed a single layer PCB, but in order to achieved the anti-noise requirement below is the criteria needed take in consider

I The connection or track of the Xbee Chip must located at the bottom layer of the PCB board, in order to effectively reduce the noise, lower down the communication latency, ensure the data transferring is in highest performance.

II The track between components is better that keep as short as possible example the connection of crystal oscillator can microcontroller. Beside that the hold also had to keep as least as possible, the purpose is to reduce the magnetic field's interference between the track.

III The Clearance of the high power signal and low power have to take in consider example for the UL/IEC 60950 state that creepage between primary and low voltage circuit should be 6.4 mm minimum. [16], besides that also have to ensure that both tracks are not in parallel, the purpose is to increases the immunity to noise in the circuit

IV Minimize areas and lengths of the loops to ensure that the circuit in not easily receive the noise from the environment.

4.8.2 PCB Construction Procedure

Before reach the stage of PCB construction stage, author had done few steps for his project. The software his uses is Altium Designer Winter edition or formally as known as Protel. First step is constructing the circuit block diagram, it is the most simplify circuit for the system. Next was the schematic diagram, the schematic diagram shown all the component and how the circuit in detail, after do the double checking that all the component value and name, had labels it correctly. Final stage is the PCB construction in this section author will describe how to make a PCB by hand.

After the PCB had been successfully constructed, the circuit is printed at PCB film, just by a normal printer. But keep in mind that the print had to be print in mirror direction because the end produce produced would be bottom of the PCB instead on the top of the board. Second is the printed circuit should be print at the rough surface of the PCB film.

While waiting the film dry, the procedure proceeded to preparing a PCB Board which make by copper and the fiber glass. Due to the surface had been corroded a sand paper used to remove the corroded surface.

The result after the PCB board's corroded surface is shown on the figure ??? .The purpose removed the corroded surface is to make sure that the circuit is "print" on this board in the good condition.

Place the prited film on the PCB board with the rough surface facing down. Adjust the position of the film correnly, the four corner and the middle part of the film's edge is tapped by the masking tape, to ensure that the film cannot be moving.

After the posting is in good manner , the iron is used to "print" the circuit from the film to the PCB board, the step have to do in slow and steady to make sure that all the printed circuit if fully printed on the PCB board surface

The film is removed slow and steady, figure ??? shown the final result of the PCB board, the board connection is checked properly the ensure did not have any brooked connection or unwanted connection, if the connection is brooked the marker pen is used to do the touchup.

The PCB is putted into the etching machine for around 10 minutes. The unprotected region's copper layer is etched out with the strong hydrochloric acid. Figure?? shown the final result after the etching process. Due to the using the strong acid and the acid is emit the danger smelly along the process a hand glove and mask must use for healthy purpose.

After the etching process, water was used to rinse the excessive hydrochloric acid, the end result shown on the figure???.

In this step, after clean up the PCB with the water, now is to remove the protected area or un etch region, this area is removed by using thinner and a small brush as shown on figure??.. , and it rinse again with water to clean the board again.

After the PCB wad dry the PCB was drilled according to the design, and the connection had be tested with digital multi-meter to ensure that the connection is according to the design, due to the etching process the connection might be shorted or disconnected, After the inspection the electronic component were soldered according to the PCB layout arrangement.


The software development take very important part in this project it is to integrate all the hardware become more applicable beside that it was the most time consuming part of this project, so choosing the correct software can ensure that the hardware is fully utilized in proper manner and use lesser time in debugging. In this project the software development were divided into two parts. First is the configuration of Xbee Series 1 transceiver, which is using X-ctu from Digi International. Second is the microcontroller programming, which is using Arduino Development Environment.

5.1 Xbee Series 1 Initial Configuration