Understanding NOR Gate (CD4001)

CD4001 is the most commonly used Complementary Metal Oxide Semiconductor (CMOS) chip. It comes in a 14 pin Dual Inline Package (DIP). It has small notch on one side which is identified as pin 1.It consists of 4 independent NOR gate in a single chip. Each gate has 2 inputs and 1 output. Working voltage range of IC is from 5V to 15V. It can deliver approx.10mA at 12V but this can be reduced as power supply voltage reduces.

IC consists of 14 pin where pin numbers 7 and 14 are connected to battery or DC power supply. Negative is connected to pin 7 and pin 14 is connected to power supply. As we know it has four gates we call it NI1, NI2, NI3, NI4. In first gate NI1 pin 1 and 2 are for inputs and pin 3 is for output. As you can see in the circuit below.

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Fig. 1: Circuit Diagram & Truth Table For NOR Gate (CD4001)

As we can see in the truth table it will provide the output equal to one when both of the input is low. In another words we will receive the high output when both the signals goes low. And if any the inputs are high we will receive the low output.

The circuit describe below can be used in many application like it can we use as fake light to create an impression that alarm has been fitted or you can use it in your vehicles when your car broke down as it will give eye catching appearance to the car passing near to your vehicle.

To understand the working of NOR gate first built the circuit on breadboard or assemble the circuit on zero PCB as it require very less components so it can be done easily.

In the diagram above consider that we have supply logic low to pin1 of NI1 as a result we will receive logic 1 in output pin 3 if you have assume pin 2 of NI1 be low. Therefore we will receive logic 0 at output of pin 4 because 1 is passed to NI2 gate input from pin 3 so whatever may be the input from pin 2 we will receive low at pin 4. This means that we will receive 6V at pin 4. As a result current start following in capacitor and capacitor starts to charge.

Now voltage on pin 8 is also low at this time and assume voltage on pin 9 to be low as a result we will receive high at pin 10 of NI3 which also make pin 12 and 13 of NI4 to high and we will receive low on pin 11 as you can see from truth table and LED connected to it will not glow.

But as capacitor charges voltage on resistor drops to half the power supply NI1 detects a high on in its input pin 2 as a result logic 0 appear on pin 3. Now logic 0 is on pin 5 ad 6 we will receive logic 1 at pin 4 of NI2. As a result pin 8 is also high and now again assume pin 9 to be low now we will receive 0 at output pin of NI3 and as a result output pin ofNI4 will receive high and LED start glowing. From above we can see that for a certain period of time circuit will work and then goes off. Time period of operation can be determine by-T=.7*R*C.

If we assume pin 9 of NI2 to be high then also we will get pin 0 to be high and low as you can now see from truth table.