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An electronics firm wishes to introduce a range of low cost alarms. You have been asked to design and produce a prototype for further development by the firm.

Extracts from this document...

Introduction

Electronics Folder Problem An electronics firm wishes to introduce a range of low cost alarms. You have been asked to design and produce a prototype for further development by the firm. Possible Projects Brief I have decided to design and make a prototype low cost home burglar alarm. Research into Alarms 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. Task Analysis 1 Task Analysis Detecting Burglars Task Analysis Warning People and making the signal last Task Analysis Getting out of the house and switching the alarm ON Task Analysis Getting into the house without sounding the alarm and switching the alarm OFF Specification My alarm circuit must do the following things: * It must sense burglars entering through the rear door. * It must sense burglars passing down the hallway. * It must sense burglars entering through the front door. * It must sense burglars climbing the stairs. * It must sound an alarm that can be heard 50m away (108dB plus). * It must sound for 4 minutes. * It must allow the householders 20 seconds to enter the house before the alarm sounds. * It must allow householders to leave the houses without triggering the alarm. * It must be possible to reset the alarm at any time to stop it sounding. * It must give the householder a quiet audible signal that it has been triggered before the main siren starts to sound. ...read more.

Middle

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. 30 min. I didn't know how to use the multimeter Learn how to use the multimeter 20 min. Alpha building and testing manual and multi-meter. TEACHER 10 min. None Insert and solder the last transducer driver and buzzer (I will use a standard buzzer not the 108dB siren). I will fit the siren later 10 min. Soldering iron, stand, pliers, cutters. Heat mat and solder. 10 min. None Test the correct working of the transducer driver and buzzer 10 min. Alpha building and testing manual 30 min. The buzzer didn't work Diary 2 Repair the transducer driver and buzzer ? Alpha building and testing manual and multi-meter. 20 min. The buzzer was soldered in upside down. Solder the reverse switch components in place 10 min. Soldering iron, stand, pliers, cutters. Heat mat and solder. 5 min. None Test the correct working of the reverse switch 10 min. Alpha building and testing manual and multi-meter. 10 min. None Solder the first switch components in place 10 min. Soldering iron, stand, pliers, cutters. Heat mat and solder. 5 min. None Test the correct working of the first switch 10 min. Alpha building and testing manual and multi-meter. 10 min. None Solder the second switch components in place 10 min. Soldering iron, stand, pliers, cutters. Heat mat and solder. 5 min. Test the correct working of the second switch unit 10 min. Alpha building and testing manual and multi-meter. ...read more.

Conclusion

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. Testing 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. Testing 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. Testing 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. Testing 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. Do not copy, use these ideas A* L33T_CS Y11 project folder Page 1 ...read more.

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