6/20/2023 0 Comments Alarm keypad layout![]() The operation op CMOS 4081 is demonstrated by pressing the A key which will cause Pin 1 for a period of time to be high and will enable gate 1. For turning OFF the alarm, correct combination of keys A, B, C, D, and E will have to be done again. This will cause the LEDs to light as the 12 V output switches from OFF to SET position. Q6 receives its current through R12 provided on the base by the relay as it holds itself while being energized. ![]() The switch Q6 will turn ON when the current passes through resistor R11 while capacitor C1 and resistor R2 sets the time for about 10 seconds. Using the 4 keys, A, B, C, and D, the alarm can be set by pressing the keys in the right arrangement. To start setting the keypad, 5 keys will be chosen as the code and will be connected to the points A, B, C, D, and E while the other keys are directed to point F and resistor R1 holds the common wire lead. This circuit may also go well with the modular burglar alarm system. ![]() Like the 12-key keypad, there should be 13 terminals present and not the 7 or 8 terminal matrix type. In choosing the component to be used in this circuit, the types of keypads recommended are those with each key in a separate connection but with a common terminal. CMOS 4081 – a quad dual input AND gate in a 14-pin package generally characterized with small fluctuation, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption.BC547 – NPN small signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selections.Burglar Alarm – one way of preventing break in’s into one’s property, not only to protect the possessions but the occupants as well can prevent the havoc and disruption caused by theft and break-in’s.Light Emitting Diode (LED) – a semiconductor diode that is commonly a source of light when electric current pass through it.Keypad – a set of buttons arranged in a block which usually display digits and other symbols but not a complete set of alphabetic letters.The circuit was designed to illustrate the operation of an electronic keypad to be utilized in the burglar alarm system by having five keys as the security syntax.
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