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Bicycle Alarm Project

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Introduction

Bicycle Alarm Project BTEC National Diploma Final Year Project By: Stewart Watkiss June 1996 Contents Page Introduction ... 1 Specification ... 1 Meeting specifications ... 2 Circuit description ... 3 Keypad and PIN decoder ... 3 Alarm set indicator ... 10 Set and part set selection ... 12 Alarm status decoding circuit ... 13 Karnaugh map ... 14 NAND only solution ... 15 NOR only solution ... 16 Monostable hold ... 18 Sounder ... 19 Low battery indicator ... 20 Circuit Diagram ... 21 Printed circuit board ... 22 Circuit additions ... 23 Price List ... 24 Problems encountered ... 25 Bibliography ... 26 Bicycle Alarm Project Introduction The crime rate in the UK is high and thefts pedal bicycles is on the increase. The reason for this increase is due to the increase in the cost of the bikes (many bikes now cost around �300), and due to the lack of security devices for bikes. The conventional bicycle lock is prone to thiefs who can break the chain links with a pair of bolt croppers. The bike locks also suffers in that it cannot protect against the theft of the bicycle lights or other attachments. The solution to this is an intelligent burglar alarm that can detect both the movement of the bike or the removal of accessories. Specification The need for an alarm is evident and so a list of specifications has been drawn up indicating what the circuit has to meet up to. Although there are no commercial bike alarms to compare this system with there have been a couple published in magazines for hobby electronic enthusiasts, these turned out to be very simple devices that were often activated while trying to turn the device off. The local police force were contacted for any advice and the following list of specifications has been drawn up. 1. The alarm should prevent theft of the bicycle. ...read more.

Middle

It is very important that the NOR gates have buffered outputs, but most CMOS ICs are buffered anyway and so this is not a deciding factor. Comparison of LED DRIVERS The NOR solution is the simplest and cheapest. It also has a lower current consumption and so is used. This forms IC5B and IC5A and drives LED1. The time constant used is a 0.3 seconds giving a frequency of about 3 Hz. This is slow enough to be seen but fast enough so as it can be seen within a short time period. This time constant was given by using a 100nF capacitor and a 3.3M resistor. These were the nearest standard values. This gave a reasonable flashing rate when tested on breadboard. Set and Part set selection This is the method in which part or full set mode is selected. As mentioned earlier this is to allow protection of the night lights when they are fitted and to prevent incorrect triggering if they are not fitted. To set the alarm (regardless of part or full) IC2D was used to trigger TR1 and disconnect power from the IC. This is mentioned earlier under the PIN decoder section. The decision for set or part set is selected by means of an RS flip-flop. The flip-flop could have been obtained by two methods. One method is to use a RS flip-flop IC this method is expensive and bulky as the IC packages contain 4 flip-flops. The other alternatives is to create the flip-flop using NAND or NOR gates. The method that has been used in this case is to use NOR gates. This is as NOR gates were been used for the rest of the alarm system (see the section on the alarm status decoding circuit page 13). A simple flip-flop has been used as only the Q output is required and the disallowed state will not effect the operation of the circuit. ...read more.

Conclusion

The templates were drawn on the computer and a laser print out made. the print out was photocopied onto acetate to make a mask for photoetching the PCB. The templates used are shown below (50% actual size). Track side Component side The pictures of bicycles line up on the component and track side and was used to ensure that the two sides line up. Circuit additions As a later thought I felt it necessary to add a further circuit to prevent the alarm from being accidently triggered when the alarm is being set or if another bike is lent against it. The circuit diagram is shown below. The circuit will only trigger the alarm if 10 pulses pass through in the time taken for the shift register to count through which is determined by the resistor and capacitor and the astable circuit. The circuit was built on stripboard but due to lack of time a PCB was not made. Price list The price list is shown below: Problems encountered A few problems were encountered during the construction of the circuit. These are listed below: 1\ Problems lining up the track and component side of the PCB. This was solved at the second attempt by Sellotaping the PCB to the acetate sheets. 4\ A few of the tracks on the acetate were very thin or had holes in. To overcome this the PCB had to be touched up with etch resist pen prior to etching the PCB. 3\ A connection was missing on the PCB. As there was not enough time to build the PCB again a wire link had to be connected on the underside. 4\ Two inputs to the SR flip-flop had not been tied to ground using a resistor. As there wasn't enough time to make another PCB these have been soldered onto the back of the PCB. 5\ The connectors used to change the PIN are very difficult to use and change. The connecters were chosen as they were cheap and readily available. A better connecter should have been used. ...read more.

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