Keypad Combination Lock Relay


Posted on Jun 27, 2012

Only one out of 9,999 possible codes has the power to unlock this simple, yet effective, electronic lock. A combination lock is not just a perfect system to protect your belongings, it is also a valid system to let everyone to know that you are vigilant: an electronic system with a silicon heart is controlling the area, day and night without interruption, so everyone is warned! You can use this combination lock circuit as a replacement or in addition to normal locks. It is very handy when a group is entitled to enter a common area, as parking lots or sport resort facilities for example. It is often the case where traditional keys are expensive, not appropriate or just not convenient: not to mention when the keys need to be replaced very often (e.g. in the case of parking lots the cars can change).


Keypad Combination Lock Relay
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Compare the convenience of distributing a new access code to the requirement of making a new run of keys... This electronic lock is excellent also for locking devices powered by the electricity. A phone line, a photocopier, children's TV, a fax or a water pump: these are just a little selection of devices that can be locked with a combination lock. And did we mention the option for adding a remote control? The basic blocks of this electronic combination lock are the keyboard, the Nutchip and the relay. The keyboard counts 10 keys, labelled with numbers 0 to 9. Four keys (actually simple normalli-open pushbuttons) connect directly to Nutchip inputs IN1...IN4. If you follow precisely the schematic we give, you get the combination 6-7-8-9. Any other key sequence will lock the device until the correct sequence is entered again. The correct sequence is determined by the truth table. In order to detect wheter a wrong key has been touched or not, the remaining keys (those not included in the combination) are connected in parallel and drive input ST0. This special pin causes the Nutchip to reset and restart it from state zero (st00), regardless of current state and other pin's situation. Therefore, touching the wrong key will cause the Nutchip to restart from state zero.




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