Piezo not loud enough

Question

I'm trying to get 110dB out of a 25khz Piezo Transducer. This piezo resonates at 25khz and as per the illustration in its datasheet should emit 110dB with 10 volts and 25khz frequency.

Any assistence as to what I'm doing wrong here would be GREATLY appreciated !!

My code is bit-banging it. With an oscilloscope, I confirmed that I'm getting a nice clean 25khz square wave.

I have attached a step-up circuit to the device and am seeing 10volts across the terminals of the piezo while it is emitting it's 25khz frequency.

However, instead of 110dB, I'm only getting 50dB.

I've tried upping the voltage to 20, and still get the same volume level. The voltage is adjustable via the screw on the top of the blue capacitor on the Voltage Step Up (pictured below).

I've tried changing the duty cycle having HIGH go for 25microseconds and LOW go for 5microseconds. I've tried several combinations and a 50/50 duty cycle appears to achieve maximum volume which is 50dB.

Here's how I'm connected: 1. The inputs of the Step Up are attached to GND and 3.3V pins on the Arduino. 2. The output+ of the Step Up is connected to 1 pin of the Piezo. 3. The output- of the Step Up is NOT connected to anything. (tried to connect it to GND but it didn't change anything. 3. The other pin on the Piezo is connected to D11 on the Arduino.

I'm Running the following code:

 #include<Wire.h>

const int SPK = 11;

void setup()
{
  Serial.begin(9600);
  pinMode(SPK, OUTPUT);
  digitalWrite(SPK, LOW);
}

void loop()
{
  long startTime = millis();
  for (int i = 0; i < 25000; i++)
  {
    digitalWrite(SPK, HIGH);
    delayMicroseconds(15);
    digitalWrite(SPK, LOW);
    delayMicroseconds(15);
  }

  Serial.println(millis() - startTime);
}

UPDATE:

Ok, I am now set up to look like this:

Is this the next step (ie: Adding an Inducer) ?

score 1 · Answer 1 · edited Apr 13 '17 at 12:50

The device you pictured seems to be a switch-mode power module which will output 10V DC. Get rid of it before you do any damage.

You don't post any link to data, but I assume you mean the Transducer needs 10V peak-to-peak.

This can easily be accomplished by using 2 digital outputs, connected to the transducer, and driven in anti-phase.

The answer to Push-Pull tone code may be an answer to your problem, but may be overkill. If you just want to output a single tone it is easily done with simple code.

I don't know why you think the transducer outputs 50dB. If it really is doubling the drive voltage will only give 56dB.

score 1 · Answer 2 · answered Jun 14 '16 at 13:11

Alternatively there are COTS parts (Common Off The Shelf) which are simpler to use and may satisfy your requirements. This is just the 1st one I found (search for "5 volt piezo buzzer"). Of course you have no control over the frequency. These type of devices are just to get your attention (you didn't say what your application was for). While it works at 5 volts it is only rated at 85dB @ 10cm. It appears to contain an internal driver so (apparently) only needs 3 to 15 volts to start making noise. It is specified to draw 10mA at 12V. So be careful and measure the current (using a power supply, not from an Arduino) demand at 5 volts. I think the GPIO pins on an Arduino can only handle less than 40mA. So stay well below that to be safe.

Piezo not loud enough

2 Answers2