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In our home devices are controlled with help of switches,sensor .Sometimes it dangerous if it physical contact with home appliances.To overcome these drawback the Light Dependent Resistor is replaced here so just pass the hand near to the LDR then the device is ON and to turn OFF again pass the hand above LDR is placed.
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The circuit has two 2 ICs namely LM714 and CD4027.The LM714 is an operational amplifier is used to compares the voltage while the hand is pass above LDR .The CD4027 is JK Flip-Flop work on master and slave concept,to give the state when the signal is given to any one of the input terminal and output is more than one.it consist four input pins JK flip flop as J and K along with set and reset pin and Qand Q¯ minus for output.
LM741 which is like a comparator for voltage ,LDR.There will be a reference voltage which is applied to non-inverting terminal as well as to LDR.The inverting terminal is connected with capacitors ,with a few additional components.
The whole circuit consists two mains parts ,few additional components for the voltage maintenance so it is easily to understand the operation of the circuit.The circuit is OFF until the hand is passed over the LDR.So the inverting terminal is in high state and the output side the pin is in low state.
The hand is pass near the LDR moves to high state compares with reference voltage ,in output terminal goes now high which supply a clock pulse to JK flip flop.With the positive going cycle so the clock changes occur. Set and Reset pin are not dependant on the clock and it started when high signal is provided to any one of the input pins.A diode is provided for the forward conduction to avoid the reverse voltage to the circuit .
In addition to the BC547 is connected to the JK flip flop terminal output is in high state means the transistor is connected to the relay the appliances can be connected via relay its get turned ON and OFF.
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The LM741 series are general-purpose operational amplifiers which feature improved performance over industry standards .The amplifiers offer many features which make their application nearly foolproof: overload protection on the input and output, no latch-up when the common-mode range is exceeded, as well as freedom from oscillations. The LM741C is identical to the LM741 and LM741A except that the LM741C has their performance ensured over a 0°C to +70°C temperature range, instead of ?55°C to +125°C. It has the overload protection on the input and output.No Latch-Up When the common-Mode Range is Exceeded.
The CD4027 dual J-K flip-flops are monolithic complementary MOS (CMOS) integrated circuits constructed with N- and P-channel enhancement mode transistors. Each flip-flop has independent J, K, set, reset, and clock inputs and buffered Q and Q¯ outputs. These flip-flops are edge sensitive to the clock input and change state on the positive-going transition of the clock pulses. Set or reset is independent of the clock and is accomplished by a high level on the respective input. All inputs are protected against damage due to static discharge by diode clamps to VDD and VSS.
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