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An enhanced four alarm keypad circuit

2016-02-19 09:53  
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This article describes an enhancement of the four alarm keypad circuit. This circuit is not new, but it proved so useful, simple and cheap, it is worth building. Keypad must be of the kind common terminal and a separate connection for each key. In a 12-key pad, look for 13 terminals. Matrix type with 7 terminals will not do. Alarm setting press a key. Select the key you want to use, and connect it to "E". Select the keys you want to use four off the alarm when they are connected to the "one BC & D '. Your code can contain non-numeric symbols with a 12-key pad, over 10 000 different codes are available. line common to all the remaining keys of R1 and F. When the "E" voltage, current through the switch Q5 in D2 and R9. energises the relay, and has its own by providing a base current of Q5 through R10. 12 volt output is to use a "OFF" to "Settings" terminal, and LED lights. off at the alarm time and necessary A, B, C and D are in the correct order. IC is a four 2-input AND gate, a Cmos 4081. these gates generate only one High output when both inputs are high. Pin 1 is determined by R5 aloft This "so that the" door one, so when 'A' at the output at pin 3 will be high and this output and two jobs. it locks itself high, it enables the door to use R2 2 through pin 5 high. remaining gates operate in different ways, each lock itself through a resistor to a successor. If you enter the correct code, the pin 10 will switch Q4 and so connected to the ground base. Q5 Q5 off and this causes the relay drop out. any key is not connected to "a BCD and E" is connected to the base of Q3 R7. Whenever these "error" key is pressed, the third quarter of need Pin 1 is low. This eliminates the "Enable" from the door 1, code entry process fails if the 'C' or 'D' in order of precedence, Q1 and Q2 will be off a low, same result. You can modify the code through change the keyboard if you need a more secure code use a larger keyboard and more "wrong" key to connect to F. a 16-key pad gives over 40 000 different codes. displays all the components on the board lie flat, but some are actually mounted upright. This link is bare copper wire assembly side. both links must be installed in the integrated circuit of the circuit is very simple, we want to help you. (BC547 )

4 digit keypad


Veroboard Layout




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