![]() ![]() The Support Material for this circuit includes a step-by-step guide to the construction of the circuit board - a parts list - a detailed circuit description - and more. If you make a mistake while entering the code - simply start again. Legend for the security system hardware includes distribution panel, window-door contact, sonic detector, key pads, heat detectors, smoke detectors. A 16-key pad gives over 40 000 different codes. If you need a more secure code - you could simply use a bigger keypad with more "Wrong" keys wired to "F". With a 12-key pad - over 10 000 different codes are available. If "C" is pressed before "B" - or "D" is pressed before "C" - the attempted code entry will fail. The same thing happens if "C" or "D" is pressed out of sequence. Whenever one of these "Wrong" keys is pressed - the attempted code entry fails - and the code entry sequence is reset. The remaining keys - those not wired to "A B C D & E" - are connected to "F". The green LED is also extinguished - to indicate that the alarm is switched off. When you press keys "A B C & D" in the right order - the relay de-energizes - and the 12-volt output returns to the "off" terminal. It provides a visual indication that the alarm is set. When you press "E" the relay energizes - and the 12-volt output moves from the "off" to the "set" terminal. Wire the common lead to R1- and all the remaining keys to "F". Choose the four keys you want to use for your security code - and connect them to "A B C & D". Choose the key you want to use - and connect it to terminal "E". The relay is energized by pressing a single key. On the Support Page you'll find details of how to Make Your Own Keypad. The matrix type with 7 or 8 terminals will NOT do. The Keypad must be the kind with one common terminal - and a separate connection for each key. Schematic Diagram Click Here For A Photograph Of The Prototype If you require added security - A Five-Digit Version - of the circuit is also available. The circuit was designed to control the Modular Burglar Alarm System - but it will have other applications. Entering a four-digit code of your choice - will de-energize the relay. Pressing a single key on the keypad - will energize the relay. Although it's designed to operate the Modular Burglar Alarm - it will have other uses. How To Build A Simple Alarm Control KeypadĪll the information you need to build a simple keypad operated switch. ![]()
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