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An electronics firm wishes to introduce a range burglar alarms. This coursework contains the design and a prototype, which has been made for further development by the firm.

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Electronics Coursework Problem An electronics firm wishes to introduce a range burglar alarms. This coursework contains the design and a prototype, which has been made for further development by the firm. Possible Projects Brief I have decided to design and make a prototype of a home burglar alarm. Research into Alarms - I have phoned companies, talked to staff at electrical shops, to find the following information. Analysis of commercial alarms From my research into commercial alarms I have found out the following... * All alarms have more than 1 input. * All alarms sound for a time after they have been triggered. * Most alarms sound for a variable time of between 2 minutes and 20 minutes. * All alarms have a sound output of at least 98dB. * All alarms have either a delay between being switched on and being armed or they can be remotely switched on and off from outside the premises. * The better alarms have a small delay between being triggered and the siren sounding. Research into Burglaries - To Catch a Thief The following research came for the television programme 'To Catch a Thief'. The presenters are ex-burglars, who have decided become good to help people prevent burglaries. First the ex-burglars find a house, burgle them (with the householders permission), and then the BBC pay for extra security to be fitted e.g. Burglar alarm, new locks, windows, and doors. Finally, the burglar is back for the last time to see whether or not he can get in. * A burglar will go for any kind of house. * Burglars go to upmarket places because the bigger the house, the bigger the 'whore'. * Burglars will go for 'posh' neighbourhoods o Three cars on the drive, shows his wealth * Secluded areas are more vulnerable because there is less chance of someone reporting a burglary. Burglars don't like public areas. ...read more.


resistor 62-0409 0.01 2 push switch 78-0100 0.20 1 key switch 79-0295 1.60 Total �1.92 PROCESS Double Delay Unit LARGE ORANGE 1 4098 i.c. 83-0426 0.25 1 16 pin chip socket 22-0160 0.06 1 1M? preset 67-0160 0.08 1 4M7? preset 0.20 1 33k? resistor 61-0409 0.01 1 47 ?F Cap. up to 24 s 11-0325 0.03 1 100 ?F Cap. up to 50s 11-0245 0.03 Total �0.66 PROCESS 4 INPUT OR GATE LARGE BLUE 1 4072BE i.c. 83-0316 0.20 1 14 pin chip socket 22-0155 0.05 Total �0.25 DRIVER Transducer Driver LARGE YELLOW 1 MPSA 13 Darlington 81-0142 0.04 1 33k? resistor 62-0409 0.01 Total �0.05 OUTPUT Sound 1 75 dB Buzzer 35-0035 �0.58 1 108 dB Miniature piezo siren 35-0272 �3.29 4 self adhesive p.c.b. pillars 33-2135 �0.09 Total �7.26 Plan 1 Plan 2 Diary 1 Task Est. time Tools and equipment needed. Time taken Problems encountered Use 2-D Design to produce layout of final circuit 20 min. Computer 2-D Design and final system diagram. 60 min. I didn't know how to use the double timer and had to ask my friends Print 2-D Design layout. 5 min. Computer 2 D Design printer 5 min. None Mill printed circuit board using CNC milling machine 15 min. Computer CNC milling machine and copper board. 60 min. I had to wait for the milling machine Drill p.c.b. 10 min. Mini drill. 20 min. None Clean p.c.b. with wet and dry paper 5 min. Wet and dry paper 5 min. None Produce parts list 10 min. Computer Microsoft Works and printer 40 min. I couldn't find where the correct values for the double delay unit. The database didn't seem to have the values I wanted. I couldn't find the correct components for the delayed arming part of the system Solder power connector components in place. 40 min. Soldering iron, stand, pliers, cutters. Heat mat and solder. 10 min. None Test the correct working of power connector. 50 min. Alpha building and testing manual and multi-meter. ...read more.


Test - burglars climbing the stairs. The pressure pad circuit worked with 100% accuracy. However it was possible to ascend the stairs and step over the pressure pad. Burglars would probably climb stairs one at a time. Therefore this system should work every time. Test - burglars entering the front door. The pressure pad circuit worked with 100% accuracy. However it was possible to leave the house without triggering the alarm. It must sound an alarm that can be heard 50m away. I triggered the alarm and tested how far away that it could be heard. With the door open I could hear it 75metres away. With the door closed I could hear it 55metres away. Test - the timer The timer ran for between 3 minutes 10 seconds and 3 minutes 40 seconds. The average time was 3 minutes 35 seconds. Although this was below the specification it was not seriously below specification and the discrepancy was probably due to the low tolerance capacitors used. Test - the 20-second entry timer I adjusted the preset on the first part of the double delay unit and arrived at an average time of exactly 20 seconds. Resetting the alarm Pressing the reset button stopped the alarm 100% of the time. Test - the quiet audible signal. The standard buzzer could be heard 15 meters away. My system therefore meets the specification in almost all ways and meets the specification in all-important ways. To improve my system I would do more research into timers and find one that could time for longer. The 555 timer can time up to several hours and this would seem to be what I need but it is difficult to make it edge triggered. Use of Industrial practices I used a lot of CAD/ CAM when making my project. I used croc clips to produce a virtual circuit and used 2D Design to design the layout. I used a CNC milling machine to cut my circuit board and could use the file to produce many identical circuits. I could never have designed such a complex circuit without the CAD/CAM equipment. ...read more.

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