# Pressure signal

#### Doppler2902

Joined Sep 15, 2020
31
Hi, I'm trying to get this pressure signal with operational amplifiers for a school lab but I don't know how I could get the sine waveshape of the signal which is a noise signal, I know that I obtain the square wave shape through a comparator configuration, any advice is helpful!

#### ericgibbs

Joined Jan 29, 2010
14,659
hi Doppler,
E

#### Doppler2902

Joined Sep 15, 2020
31
This is what I'm doing, comparing two voltages levels for get the square wave form

#### crutschow

Joined Mar 14, 2008
28,507
You can run the signal through an RC high-pass filter to reduce the sinewave noise.
Pick a filter corner frequency somewhere between the sinewave frequency and the pulse rep frequency.
A lower frequency will suppress more of the sinewave, but also distort the pulse more, so you look for the happy medium.

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#### Doppler2902

Joined Sep 15, 2020
31
You can run the signal through an RC high-pass filter to minimize the sinewave noise..
Yes, but I'm obtaining only the square wave, my question is how to obtain the sine waveshape, adding noise?

#### Irving

Joined Jan 30, 2016
2,411
I'm guessing this is an experiment for the students to find ways to recover the wanted signal in the prescence of noise (hum, etc)?

What signals are you applying at S1 and S2? That's a complicated way to get a simple fixed pulse train...

Is the sine wave 'noise' related in frequency/phase to the pulses or should it be different (ie non-coherent noise)?

#### ericgibbs

Joined Jan 29, 2010
14,659
hi Doppler,
I would add another 741 to the output of the comparator circuit, sum/mix the Sine wave and the Square wave signals that way.
Do you follow, OK.?
E

#### ericgibbs

Joined Jan 29, 2010
14,659
hi Doppler,
This will give the basic idea, as this is homework you can finalize the circuitry.
E

#### Doppler2902

Joined Sep 15, 2020
31
hi Doppler,
This will give the basic idea, as this is homework you can finalize the circuitry.
E

View attachment 252535
Alright, I got the idea, thanks

#### ericgibbs

Joined Jan 29, 2010
14,659
hi D,
OK,
E

#### Doppler2902

Joined Sep 15, 2020
31
hi D,
OK,
E
Alright, the main idea is get the comparator signal and then add the noise which is the sine wave, and I can get the Pressure signal that I need?

#### ericgibbs

Joined Jan 29, 2010
14,659
hi D,
I would suggest you do not use the term 'noise' if the modulating signal is a sine wave form factor.
What is the source of the Sine wave which you are using to drive the comparator input.?

E

#### Doppler2902

Joined Sep 15, 2020
31
hi D,
I would suggest you do not use the term 'noise' if the modulating signal is a sine wave form factor.
What is the source of the Sine wave which you are using to drive the comparator input.?

E
Oh, I was saying noise because I have to filter that signal for obtain the blue signal

#### Irving

Joined Jan 30, 2016
2,411
Here's my take on generating the test signal...

#### Doppler2902

Joined Sep 15, 2020
31
hi D,
OK,
E
This is what I have now

The problem is that I'm making a filter for delete the sine waveshape, I' ve tried with the double T filter but I have some armonics in the signal

#### Doppler2902

Joined Sep 15, 2020
31
This is the filter that I've implemented

#### ericgibbs

Joined Jan 29, 2010
14,659
hi D,
Do you know the frequency 'range' of the sine wave input and is the amplitude fixed.?

The filter you have will affect the 'square' wave shape.

E

#### Doppler2902

Joined Sep 15, 2020
31
hi D,
Do you know the frequency 'range' of the sine wave input and is the amplitude fixed.?

The filter you have will affect the 'square' wave shape.

E
The frequency of the sine wave is 500 Hz and the square wave is approximately 8 kHz