OP-AMP (non-inverting) - LM324

An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. (WIKIPEDIA)

Amplifier is a device which takes small voltage in input terminal and spits out large voltages in output terminal...

the gain of amplifier is the amount multiplied with input to produce the desired output...

for example if u take a 1V input and get 5v output then the gain of amlifier is =5

an OP-AMP has generally 5 important pins

i> inverting input 
ii> non-inverting input
iii> +Vcc
iv> -Vcc
v> OUTPUT

in input terminal only use signals ...

OP-AMPS can't creat voltage out of nothing!!! so we have to use a bit larger supply volatage than the desired output voltage

so if i have to get a 10V oupput then i have to use atleast 12V supply voltages... dont try to apply high voltage it may damage your device so always reffer the DATA SHEET


if your supply voltage s very less then you will get clipped OUTPUTS



smooth voltage sources are important for a amplifier to give a uniform output signal so use two suopply batteries, hooked up in series  with capacitors given below :

CLASSIC NON-INVERTING AMPLIFIER:


here we use a LM324 OPAMP with max current rating = 20mA

you can set the gain using resistors ...
the circuit diagram is given below

THE GAIN FORMULA :

for simplicity use R1=1k (fixed) and then choose R2 according to you gain......

CLICK HERE for the derivation of the gain formula ( find it in thr 9th page )

APPLICATION:

SPY-MICROPHONE

 a simple small microphone has a output signal of 20mV
and to run a EAR-BUD we need atleast 2V
so gain must be 100

using gain fomula r2= 100k
so gain= 101 nearly equal to 100

OK TIME TO UNDERSTAND THE CIRCUIT BLOCK BY BLOCK :

BLOCK A
use 9V supply to power up the mic and use R1 to limit the current

BLOCK B
is a high pass filter and the capacitor blocks the supplied 9v DC and passes the signal

BLOCK C
r2 and r1 is set to a gain of 100
so in output pin we get a 2V signal 

BLOCK D
10K variable resistor is used to change the supply voltage of LS(ear-bud) to control the volume 



2V output is sufficient to run the earbuds but can't run a LOUD SPEAKER as a loudspeaker needs high power supply which will kill the LM324 ..... so i have googled for a home theater OPAMP and found LM1875 OPAMP, which is great for loud sounds in your home.....you can supply more voltages and use high valued resistors to get LOOUUDDDDD SOUNDDDDDD!!!!!!!!!! the circuit diagram is same for both LM324 N' LM1875



DERIVATION OF GAIN( NON INVERTING) 
*video will be uploaded soon 

RC-LOW PASS FILTER

© Aditya Narayan Nanda

LOW PASS RC FILTERS:

WHAT IS THIS??

FILTERS are used to change the frequency content of a audio ... that means u can clip off some of the frequency( in some range) and pass others .. wow!! sounds great.....

understand any thing??? i know your ans is NO!!!

so lets see this practically::

first download VLC MEDIA player and open the song : given up by Likin park

i choose this one because this band is my fav and songs have almost every frequencies ... cool na??

OK now play the song and go to the equalizer control and then change the frequency bars as shown...

(CLICK HERE TO GET A MAGNIFIED VIEW)

have you noticed any change in sound?? probably your answer is YES..

its just like your pre-loaded FULL BASS mode.  

look at bar setting what you have done?? u have just allowed the low frequencies and blocked the higher ones that mean you have clipped off high frequencies and allowed lower one.. that means you have made a LOW PASS FILTER...

<<notice you can still hear the song but some frequencies are clear>>

HOW TO MAKE LOW PASS FILTERS??

u need resistor, capacitor, DC source , jumper wires and bread board

Example Circuit:

this works so because the voltage of capacitor can't instantaneously change. and you have a resistor in series which slows down the charging process: OK THAT MEANS IF RATE OF CHANGE IS HIGH then OUTPUT VOLTAGE IS NOT GOING TO REPRODUCE IT IMMEDIATELY .. BUT WHEN YOU HAVE LOW FREQUENCY THEN RATE OF CHANGE IS SLOW SO YOU GET THE EQUIVALENT OUTPUT.

IN PRACTICAL CIRCUITS YOU HAVE TO CHOOSE A HIGH RESISTANCE AND LOW CAPACITANCE TO BUILD A LOW PASS FILTER

cut-off frequency formula:

so our example filter has a Fcutoff = 1591.54 Hz that means any frequency greater then this is not going to sound your ear buds!!!

how to choose r c values for your own filter?

FIRST use the speaker data sheet and look for the max current... then look at your source DC voltage... the choose a resistor to limit the current .....then use your cut off formula to calculate the capacitor value.. very easy.... 

SOME SIMULATIONS :

below i have given 3 examples. R1 and C1 are filter elements and R2 is  a load resistance and stands for head phone or speaker etc.

in all cases R1=10K, C1=10n 

so
Fcutoff= 1591.54 Hz
::::::::::::::::::::::::::::::::::::::::::::::

1:WHEN INPUT FREQUENCY IS LOWER THAN CUT OFF FREQUENCY:

Fcutoff= 1591.54 Hz

Applied Frequency= 50 Hz

Here applied frequency(in green color) is very low so output frequency ( in red color) is same as input...

::::::::::::::::::::::::::::::::::::::::::::::

2:WHEN INPUT FREQUENCY IS HIGHER THAN CUT OFF FREQUENCY:

Fcutoff= 1591.54 Hz

Applied Frequency= 2000 Hz

Here applied frequency(in blue color) is slightly high so output frequency ( in green color) is clipped off and we get very low amplitude output...

::::::::::::::::::::::::::::::::::::::::::::::

3:WHEN INPUT FREQUENCY IS MUCH HIGHER THAN CUT OFF FREQUENCY:

Fcutoff= 1591.54 Hz

Applied Frequency= 200000 Hz

Here applied frequency(in green color) is very very high so output frequency ( in red color) is totally clipped off... so we get a nearly zero output

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NEXT TUTORIAL:

 RC HIGH PASS FILTERS then REAL AND IDEAL FILTERS