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5-Digit Alarm Keypad: Build Your Secure Circuit Diagram
Schematic Diagram
Notes
A five-digit security code can be selected, and the corresponding keys on the keypad should be linked to terminals "A B C D & E". The keypad's common terminal must be connected to resistor R1 - while the remaining keypad keys should be connected to terminal "F".
The circuit is straightforward. Upon inputting the initial four digits of the security code, the relay is activated. Consequently, a 12-volt power supply shifts from the "off" to the "set" terminal, and the green LED illuminates.
When the complete five-digit code is entered, the relay is deactivated. The 12-volt power supply then shifts from the "set" to the "off" terminal, and the green LED ceases to glow.
Any keys not connected to "A B C D & E" are linked to "F". If any of these "Incorrect" keys are pressed, the code entry process fails, and the sequence resets. Inputting the “Correct” keys in an incorrect order will also trigger a reset of the circuit. If an error occurs during code entry, the user can simply begin the process anew.
The Keypad requires a specific type - one that possesses a single common terminal and a distinct connection for each individual key. For a 12-key pad, look for 13 terminals. A matrix design with 7 or 8 terminals will not be suitable.
The Support Material comprises - a comprehensive circuit description, a parts list, a step-by-step guide for assembling the circuit board, and plans for constructing a DIY keypad.
With a 12-key pad, nearly 100 000 distinct five-digit codes are achievable. Should a more robust code be desired, a larger keypad with more “Incorrect” keys connected to “F” could be utilized. A 16-key pad would provide over half a million different five-digit codes.
More about components
The circuit incorporates an integrated circuit (IC) for enhanced functionality. This IC, specifically a microcontroller, acts as the central control unit, managing the code entry, relay activation, and LED control processes. Microcontrollers are semiconductor devices that combine processing, memory, and input/output functionality onto a single chip. They are commonly used in embedded systems where precise control and timing are essential, like this security circuit, because of their ability to process data and respond to events quickly. This IC typically includes features like a programmable timer, digital input/output pins, and a built-in clock, allowing it to manage the entire code validation and control system within the circuit.
Veroboard Layout
