Question

OK LED 10K [ In the debouncer switch circuit connected above explain the behavior of the LED when you pressed pulser A many times and then did the same to B many times.

Answer 1

Lets consider debouncer circuit shown below, The debouncer circuit consists of an SR latch, or simply we can say that it consists of Two Nand Gates where one Nand Gate output is fed back into another Nand Gate input. Before analysing the circuit lets take a look at the truth table of the Nand Gates Input Input Output 0 0 0 1 0 From this we can say that the output of Nand gate will be high, if any of the two input is low Now lets analyse the circuit if the Push Button A is pressed Initially when A is pressed we can say that, Top Nand gate is connected to GND and Nand gate at bottom is connected to +5 v supply.

We already know that when any one of the input in Nand gate is low, then the outpur of that Nand gate is High.So we can say that the output of Top Nand gate is high. Now this High output of Top Nand gate is Fed back toanother input of Bottom Nand gate, thereby making two inputs of bottom nand gate as higlh therefore we can definitely say that the output of the bottom nand gate is Low. (Using truth table of Nand Gate) Now this output of battom Nand gate is fed back to the another input of the Top Nand Gate. But the output of the Top Nand Gate doesn't changes Now When the Push Button A is released, The one input of Top Nand Gate becomes High and this change will not change the output of the Top Nand Gate. Now When A is pressed or released this will not change the output of the circuit. In our circuit, The LED is connected to the output of the Top Nand Gate, this LED will be KEEP on Glowing no matter whether A is pressed or released.

Now Lets Get into the case when push Button B is pressed when push Button B is pressed, the one of the input to the Top Nand Gate is High and the one of the input connected to the bottom nand gate is low already we know that when any one of input to Nand gate is low, then the output will be high. ie output of bottom nand gate is High This high output of bottom Nand gate will be fed back to the input of Top nand gate and the two inputs to top Nand gate will be High When Two inputs are high then output of Top Nand gate will be low

Even when this Low output is fed back to the Bottom Nand gate, the output of bottom Nand gate will remain High. en pressed or released. Therefore we can say that, The LED connected to the output of top Nand Gate wil be always in OFF state since the output of the top Nand Gate will be always Low no matter when B is pressed or released. Finally we can confirm that when A is pressed and released for many times, the LED will be Glowing (ON) once the circuit attains steady state. When B is pressed or released for any times, the LED will be in OFF state once the circuit has attains a steady state.