### Analog Circuits

"Nothing is simple until you are good at simple issues"

contents:

=> Op-amp based Automatic room light controller circuit
=> Op-amp based automatic fan controller circuit
=> Coffee machine controller circuit using monostable multi-vibrator   etc.,

OpAmp(Operational Amplifier): is an amplifier which can amplifies the difference between the two input signals applied to its inverting and non-inverting terminals.
where 'Ad' is OpAmp Gain and
Vd=V1 - V2

OpAmp has many applications, some of the things were classified here

we will go through some of these applications
the total simulation part is done in proteus software
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1). OpAmp as a comparator:
OpAmp can be used as comparator in Open-loop configuration. Since the OpAmp has two input terminals inverting and non-inveting we can use it for comparing voltages.

am showing here a simple example, here am converting sin wave into square wave.
am using
uA741 OpAmp with +Vsat=+15v and -Vsat=-15v
sin wave input 6V amplitude and 1Hz frequency

here you can see that am giving sin wave to non-inverting terminal and i put a threshold voltage 1.5V at inverting terminal. so that whenever the sin wave exceeds the threshold the output will be +Vsat=+15V otherwise the output is -Vsat=-15v

Vsin > 1.5v then Vout= +15v
else   Vsin < 1.5v then Vout= -15v
the output of the above circuit is follows here  to see output
here i have plotted both input sine wave and output square wave with respect to time.
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Automatic Room light Controller using OpAmp:

It is more important to save power. here the one way to save the power by automatic controlling of room lights. This is also an application of OpAmp based comparator. This is based on the light intensity in the room, here we use LDR(light dependent resistor) who's resistance decreases with increase in room light intensity. There is a choice that you can change the threshold level to your desired level so that it can operate at that intensity level. It does not require any microcontroller or any other programmable devices.

components procured:
>LDR
>OpAmp 741
>resistor 10k
>BC547 transistor
>SPDT relay 12V
>1N4001 diode
>battery and a bulb

here i connected the LDR output to the inverting terminal and a threshold voltage of 1.5v is connected to the non-inverting terminal. so that whenever the light intensity increases the LDR output will decrease and if it is less than the threshold the output of the opamp will be +Vsat=+5v.This will trun on the BC547 so that relay will be connected as shown here, bulb will not glow
VLDR >1.5v ; transistor ON; Light OFF;
to see the output

when the room light intensity decreases LDR resistance will decrease and voltage across the resistor goes high. when it is greater than the threshold opamp output goes to -Vsat=-5v. then the BC547 will goes to the cutoff region (OFF state). so the light will glow.
VLDR < 1.5v ; transistor OFF; light ON;

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Automatic room fan controller using OpAmp:

This is the another application of a comparator. This can save the power and we don't need to switch ON and OFF the ceiling FAN manually. here we can set the threshold voltage to our desired value. The ceiling fan will be switched ON when the temperature increases the threshold value. We are using LM35 sensor to sense the room temperature. The sensitivity of this LM35 sensor is 10mv/ 'C. I want that fan to be switched on when the temperature increases more than 27'C. so set my threshold voltage to
Vthreshold = 27'C x 10mv = 270mv = 0.27V

here the room temperature is 26'c so the output voltage is < 0.27V ; Fan off
to see the output

when the temperature increases to 27'c or more, the output voltage of LM35 will increases to more than 0.27V. so that opamp output will goes to +Vsat=+5v. This will switch ON the transistor and so relay connects. This will switch ON the ceiling fan.

here the temperature is 28'c so the output voltage >0.27v; fan ON