Hi, I need help amplifying the sound/output of this transducer. I have verified that the input of the op amp is 25 KHz and the output is as well. I just cannot get the transducer enough power.

Details:

• I'm using a LM324 Dual Op amp - http://www.ti.com/lit/ds/symlink/lm324.pdf
• I'm currently only using 1 of the amps in the LM324
• The transducer I'm using - https://www.americanpiezo.com/images/stories/content_images/pdf/apc_10-1011.pdf
• My current circuit and picture of my breadboard (attached)
• Currently using 9V alkaline battery. Will be switching to a 3.7v lipo battery.
• Image attachment IMG_1036.png is the output of my arduino.
• Image attachment IMG_1037.png is the output of op amp.

Thanks for any help or insight anyone can offer.

PS. I am pretty new to circuitry. My background is in Software Development. Please bear with me if I use the wrong terminology. Trying my best to learn.

Edit: I spoke with someone at American piezo and he said that I need to push 30 VRMS to the transducer. So I would like to do that, or at least go as high as the op amp supports.

 

Welcome to AAC!

Thank you for posting a schematic. What is the amplitude of the input signal, how is it coupled?

Some members have slow or very slow connections. Please post images with an appropriate resolution.

Clipped output waveform info:


And uninteresting Arduino output:


Breadboard - note, 9V supply, not +/-9V as indicated in schematic:

 

Datasheet ... absolute maximum ratings section ... specifies minimum supply voltage is 13 volts.

Are you referring to LM324?

 

Are you referring to LM324?
View attachment 125768

I stand corrected ... but if you want to increase the magnitude of the input/output voltage, the supply voltage will have to be increased.

 

Some members have slow or very slow connections. Please post images with an appropriate resolution.

Good point. I'll make sure to lower the resolution.

Breadboard - note, 9V supply, not +/-9V as indicated in schematic

Ahh, I didn't catch that. How can I get -9v?

I stand corrected ... but if you want to increase the magnitude of the input/output voltage, the supply voltage will have to be increased.

I replaced the 9V battery with a 30v supply, which accomplishes what I needed... a louder transducer.

Now my issue is that the square wave is distorted at the op amp output.

 

Also, I forgot to mention that I swapped out my resistors for a 100x gain as shown in 8.2.1 - http://www.ti.com/lit/ds/symlink/lm124-n.pdf

R1 = 10k
R2 = 1M

 

To get a better square wave output, try placing power supply bypass capacitors near the connections. This might consist of a 10 uF electrolytic, and a 0.1 uF ceramic, non-polar capacitor, immediately adjacent to each power supply connection.

 

LM

Good point. I'll make sure to lower the resolution.



Ahh, I didn't catch that. How can I get -9v?



I replaced the 9V battery with a 30v supply, which accomplishes what I needed... a louder transducer.

Now my issue is that the square wave is distorted at the op amp output.

View attachment 125782

You need faster opamp.
LM324 can output at 25kHz only about 5V peak to peak undistorted sine wave.

 

Hello,

The slew rate comes into play with large signal output.
The edges will become slopes due to the speed of the opamp:



Also with higher frequencies the output may not get to the full range of the opamp:



Bertus

 

The sharp corners of square waves consist of higher frequency sine waves. If those sine waves are attenuated ... not amplified 100%, then the output waveform shape will be distorted.
So, it may be that you need a different op amp, one that can deal with the higher frequency components.

 

LM

You need faster opamp.
LM324 can output at 25kHz only about 5V peak to peak undistorted sine wave.

Also with higher frequencies the output may not get to the full range of the opamp:

The sharp corners of square waves consist of higher frequency sine waves. If those sine waves are attenuated ... not amplified 100%, then the output waveform shape will be distorted.
So, it may be that you need a different op amp, one that can deal with the higher frequency components.

Thanks. That makes sense. Any suggestions on what I can replace this with? I found this chip, but cannot find a through hole version - http://www.ti.com/product/LM48580

 

The TI component looks like a possibility.
Sometimes, there are adapters that allow the utilization of surface mount and similar devices in macro applications.
So, suggest that you contact TI directly and inquire what implementation is available.

 

Any suggestions on what I can replace this with?

Older generic frequency compensated opamps have a slew rate of about 0.5V/uS.

Your application doesn't really need an amplifier, so use a comparator (LM393, LM339) instead.

 

Ahh, I didn't catch that. How can I get -9v?

You could use another 9V battery. But, from your later post, you don't need a negative supply...

 

If you want to drive a piezoelectric transducer with 25kHz 30V square wave, you don't need an opamp or split power supply. All you need is a single 30V supply and a driver transistor.

 

OP seems to be concerned with portability ... The TI LM48580 contains a built in voltage booster ... 30v and 800 mw power from a 3.6v battery.

The only issue is obtaining a ball grid array adapter socket to allow construction.

This place has socket adapters ...
info@ironwoodelectronics.com

 

The TI LM48580 contains a built in voltage booster ... 30v and 800 mw power from a 3.6v battery.

Seeing that I switched to a step up converter to use with 3.7v lipo, I could ditch the step up converter with this chip? I'm I correct in my understanding that it has a step-up converter built in? That would reduce space by a good margin.

If you want to drive a piezoelectric transducer with 25kHz 30V square wave, you don't need an opamp or split power supply. All you need is a single 30V supply and a driver transistor.

I just tried this with ~20 volts and my square wave is still distorted, though not as bad, and not loud at all, unlike when I was using the op amp. I based my circuit on this, with a TIP122 transistor:

 

Are you filtering the power supply connections ... an electrolytic and a non-polar cap at each power supply?

... Something to try ... decrease the base resistor on the transistor to maybe 500 ohms. This will turn on more current and increase power output ... Check temp of the transistor ... not too warm.

The LM48650 would have a built in voltage boost. ... Just have to try it out. ... In earlier times ... TI would send a free sample on request ... not too sure about now. ... Also require socket adapter for 12 pin ball grid array.

 

Show your transistor circuit. A piezo transducer is like a capacitive load. You need a pullup resistor for a load.

 

Thanks. That makes sense. Any suggestions on what I can replace this with? I found this chip, but cannot find a through hole version - http://www.ti.com/product/LM48580

A TL084 by Texas instruments (from Mouser for under 2 bucks) will do the swing you need at the voltage you need. It is a 4 section amp like the 324, in the 14 pin dip package. A TL082 is a dual section in an 8 pin dip.