im planning a project that consists of a code circuit (for a safe say) but have no idea where to start.

i would like to have a code of about six numbers with two attempts at getting the correct code. If the code isnt correct an alarm should go off with an audible output.

if the correct code is guessed it will turn off an electromagnet and open the safe but only after a time delay of 3 minutes say

i have no idea how to approach this so any help with links or circuit diagrams is much appreciated

 

The best way to approach it, is to break it down into functional sections, and think about each section seperately.

For example, you might break it into:
1) Power supply
2) Keypad + keypad interface
3) Code checking logic
4) Timer
5) Electromagnet driver
6) Alarm output

To open the safe - instead of turning OFF the electromagnet, how about turning it ON? That way, if you have a power failure, the safe won't automatically unlock, and besides, having an electromagnet running continuously (whilst you are not accessing the safe) is wasteful of power.

If you have some programming experience (or wish to gain some), perhaps you can combine the majority of these functions into a small microprocessor (eg PIC or PICaxe).

 

Yes, a PIC is an ideal device to do this, cheap and simple - one of my tutorials (the keypad ones) does almost exactly what you want.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

If you want a Simple and pretty good lock, go to my website.
This one doesn't require a PIC.
It is only 4 digit entry, Although it can easily be expanded to 6 numbers.

http://www3.telus.net/chemelec/Projects/Projects.htm

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Shall not bore you with talk of case hardening metals / drill resistant filling material / relockers and so forth for safes. However , some method of detecting if the locked enclosure has been prised open or is suffering from a brute force attack...could be worth a thought.