I added dampening resistor which is connected through 2N7000 and will be disconnected after 200us from the transmitting phase ends. In this way I could barely read echo waves incoming on the screen.

When I focus ossciloscope at 2ms after the trigger event and set an object in front of the transducer that is 30cm away ,
the empty read graph below changes to second one.
First one - no reading
Second one - reading

 

Hi demir,
Is this a College project?
Looking at the two scope images is shows from what I can see the piezo is not being driven at its resonant frequency.
When you post scope images, it is important that the scope grid for the X and Y are visible.

What is the purpose of C5.?
The 741 is designed for dual power supplies also its limited response time is poor.

Try this simple test on your piezo, disconnect it from the circuit, place a 10k resistor in parallel.
Connect your scope across the resistor, then lightly tap the piezo with a wooden pencil, the scope should show a ringing damped exponential.
Measure the period between two adjacent signal peaks, this will give the resonant frequency of the piezo.

Post the scope images

E

 

Hi demir,
Is this a College project?
Looking at the two scope images is shows from what I can see the piezo is not being driven at its resonant frequency.
When you post scope images, it is important that the scope grid for the X and Y are visible.

What is the purpose of C5.?
The 741 is designed for dual power supplies also its limited response time is poor.

Try this simple test on your piezo, disconnect it from the circuit, place a 10k resistor in parallel.
Connect your scope across the resistor, then lightly tap the piezo with a wooden pencil, the scope should show a ringing damped exponential.
Measure the period between two adjacent signal peaks, this will give the resonant frequency of the piezo.

Post the scope images

E

Hi Eric , It is a semi collage project. The purpose of C5 is to remove the negative dc offset, looking at the circuit and think It might be unnecessary. I have tested piezos seperetaly for few times and they work well at 40Khz. The reason scope says 42Khz is I found out transmitting the last piece of burst with a delay of half a period decreases ring of piezo but In last experiment that option is removed from the code. I think I might have better results with some better opamps but at the point I only have lm741 in stock and wanted to test it. As the opamps arrive I will test them too. Also , I need to note that , In previous reply there is no X/Y axis due to they are screenshots from a video but I can repeat the experiment again.

 

I ordered some NE5532P and LF353N , seems like NE5532 also needs to supplied by 2 supplies but LF353N is suitable for my connection

 

hi demir,
This is your basic circuit in LTSpice simulation.
E

 

hi demir,
This is your basic circuit in LTSpice simulation.
E
View attachment 326971

I have few questions before I try this model myself and play with parameters.
Why is D1 and D2 are different models ? I know 1n914 is switching diode but I could not understand why D1 is BAT54.

 

HI,
The BAT54 is a Schottky diode and has a low forward voltage drop, so it clamps at a lower level.
E

 

Hi Eric , I repeated the experiment with small changes and the circuit is much more similar to yours now.
I separately measured the echo signal and obtained that when echo comes from 30cm , it's Vpp is around 20mV.
Eventhough I haven't got Av of 100 from opamp , signal was barely readable. I also made the on time of DAMP_EN longer towards 800uS and this solved ring problem perfectly I guess. The NODE B traces is almost same with your's blue traces.

Node C when no object is set.
Node C when an object set 30cm away from transducer.

 

hi demir,
Did you do that test??
E
Try this simple test on your piezo, disconnect it from the circuit, place a 10k resistor in parallel.
Connect your scope across the resistor, then lightly tap the piezo with a wooden pencil, the scope should show a ringing damped exponential.
Measure the period between two adjacent signal peaks, this will give the resonant frequency of the piezo.

 

hi demir,
Did you do that test??
E
Try this simple test on your piezo, disconnect it from the circuit, place a 10k resistor in parallel.
Connect your scope across the resistor, then lightly tap the piezo with a wooden pencil, the scope should show a ringing damped exponential.
Measure the period between two adjacent signal peaks, this will give the resonant frequency of the piezo.

I Will do that test i forgot about it sorry. The outputs for echo viewing.

 

hi demir,
Did you do that test??
E
Try this simple test on your piezo, disconnect it from the circuit, place a 10k resistor in parallel.
Connect your scope across the resistor, then lightly tap the piezo with a wooden pencil, the scope should show a ringing damped exponential.
Measure the period between two adjacent signal peaks, this will give the resonant frequency of the piezo.

Hi , here is the test you mentioned.
I guess I need to note that , the transducer is the receiver part upon the HC-SR04 so I can not tap straight onto the piezo.
I could not decide if the frequency is 40Khz or 4Khz.
What I use is something like this.

 

hi demir,
Did you do that test??
E
Try this simple test on your piezo, disconnect it from the circuit, place a 10k resistor in parallel.
Connect your scope across the resistor, then lightly tap the piezo with a wooden pencil, the scope should show a ringing damped exponential.
Measure the period between two adjacent signal peaks, this will give the resonant frequency of the piezo.

Hi Eric , opamps have been just delivered. Are you available ?

 

Hi demir,
Yes, which OPA types do you have?
E

 

Hi demir,
Yes, which OPA types do you have?
E

I currently have some LF353P , LM741. Tomorrow I will get NE5532.

 

I currently have some LF353P , LM741. Tomorrow I will get NE5532.

I am not experienced with opamp models , I guess theese are dual supply models

 

I have tried some active high pass builds but since the opamp also gains mostly dampened ringing and noises , echo is now readable but not clear

 

Some output like this

Hi Eric , I repeated the experiment with small changes and the circuit is much more similar to yours now.
I separately measured the echo signal and obtained that when echo comes from 30cm , it's Vpp is around 20mV.
Eventhough I haven't got Av of 100 from opamp , signal was barely readable. I also made the on time of DAMP_EN longer towards 800uS and this solved ring problem perfectly I guess. The NODE B traces is almost same with your's blue traces.
View attachment 326978
Node C when no object is set.
View attachment 326979Node C when an object set 30cm away from transducer.
View attachment 326980

Output appears like this ones.

 

Hi.
I guess you know that those 3 OPA types are for dual power supplies?
E

 

Hi.
I guess you know that those 3 OPA types are for dual power supplies?
E

I noticed It but the current issue i work on is differs from opa type I guess or isn't it ?

 

hi dem,
This image copy of yours is looking better, it is typical, but it is clear that the Piezo is not in resonance, at 35kHz
How are you connecting your components to the HC SR04.

Can you post a photo of the project so that I can the connections
E