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Introduction

Electronics Coursework Electronic Combination Lock Aim: * The aim of this project is too create a secure lock to protect a property from intruders. To do this I have researched how to construct an electronic combination lock. During this project I will create a lock that is a great deal more secure than a standard mechanical lock, the reasoning behind this is that an experienced locksmith can open a mechanical lock without any trouble. On the other hand an electronic lock will seem a lot more of an obstacle to open as you have to input 4 switches in the correct order to open the lock successfully increasing the security highly. Research: * I have researched some factory made electronic locks to compare with the design that I will make. Of course my project will be much simpler than some of the combination locks that I have found on the Internet. (http://www.quasarelectronics.com/3029.htm). * One of the factors of the circuits that I need to consider is what the input would be (for example a keypad or simply switches.) I have decided that a keypad as an input is too complicated to build effectively and fault finding will be very difficult, because of this I will include 4 switches as the input to make the circuit simpler and easier to build, and fault find if there are any problems after construction. ...read more.

Middle

A positive reset input forces Q to ground and Q dash positive. Should both reset simultaneously positive, both Q and Q dash will also go positive. This is usually a disallowed state. The last direct input to go to ground will determine the final state of the Q and Q dash outputs. The direct inputs override the clocked inputs. Each flip-flop may be made to binary-divide by cross coupling the Q dash output to the D input. The clock input must be noiseless and have only a single ground-to-positive edge transmission per desired clocking. Clock rise and fall times should be 5 microseconds or faster. Maximum clock frequency is 10megahertz at 10 volts and 4 megahertz at 5 volts. Total package current at 1megahertz clock frequency is 0.8 milliampere at 5 volts and 1.6 milliampere at 10 volts. Reference: taken from "CMOS Cookbook" * In my circuit I am going to use momentary switches or push button switches. A push-button switch is considered to be "momentary"; it doesn't stay in place when you remove your finger. Your doorbell button is a "normally open" (N.O.) momentary switch. When you push it, the circuit is connected and so the bell rings. ...read more.

Conclusion

The switches that aren't being used are all wired together in parallel so if any of them are pressed they reset the circuit. The switches that are being used are wired to the 4013b CMOS chips so when they are pressed a signal is sent to the next chip telling it that one switch has been correctly pressed, activating the next chip allowing the next switch to be activated. This means switches can only be input in one correct order. If this combination is not entered correctly then the circuit is reset so the combination has to be input again. * For the memory that I need to create to remember the order in which the switches have to be pressed, I am using 4013b CMOS chips. Combination Lock Circuit Diagram This circuit is relatively basic to build. To open the lock, which is connected to the K1 Load. You must press each momentary switch in the correct sequence. The sequence used in this circuit is S1,S2,S3,S4. If any of the other switches are pressed the circuit will reset and you will need to start over. Depending on How you wire the switches, you can use any 4-switch combination. Obviously I will not use the simple combination of 1--> 2-->3-->4 I will change this code appropriately. ...read more.

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