A Simple Keypad-Operated Switch - with enhanced security

Posted on Feb 7, 2014

This is a universal four-digit keypad-operated switch - with a difference. Instead of entering the security code one number at a time - the four keypad buttons must be pressed simultaneously. In other words - the four numbers must be entered in parallel. The intruder won`t know the code. He won`t even know how many digits there are in the code. An

A Simple Keypad-Operated Switch - with enhanced security
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d he almost certainly won`t know that the entire code must be entered simultaneously. Added to this - is the extra layer of security provided by the secret time-lock. After a few incorrect codes are entered - the circuit will stop responding to the keypad. And any further attempts to crack the code - will be unsuccessful. If you don`t want the time-lock feature - leave out D6, C6, R8 & R9. And connect pins 8 & 9 of the IC together. If you want to use a three-digit security code - leave out D4, C4 & R4. And connect pins 5 & 6 of the IC together. Three digits are easier to enter than four. Do not use the "on-board" relay to switch mains voltage. The board`s layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount a suitably rated relay - somewhere safe - Away From The Board. Choose the four keys you want to use for your code - and connect them to "A B C & D". Since the keys have to be pressed simultaneously - the order in which you make the connections is irrelevant. Wire the keypad`s common terminal to "Com". And connect all the remaining keys to ground. That is - to "E". The circuit will power-up with the relay energized. When you press keys "A B C & D" simultaneously - the relay will de-energize. To energize it again - press any key not included in your code. That is - any key connected to "E". If you want to reverse the action of the...

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