Voltage Controlled Voltage Source (VCVS) - Piezo Buzzer

[bcavan]

Hi, I am trying to power a Piezo Buzzer between 3.3VDC and 5VDC.
The voltage is being adjusted so the sound is low (at 3.3VDC) and loud(at 5VDC).
My attachment can be a little misleading. Alarm_low doesn't suggest the volume is low, just the number of beeps. Same holds true for Alarm_medium and Alarm_high.

I'm trying to figure a way to add a circuit like a Voltage Controlled Voltage source as observed in my attachment. Can anyone offer some advice?

Thanks,

Brian

 

[dorke]

Welcome to EP.
What specific Piezo Buzzer are you using?

 

[bcavan]

Hi there, attached is the buzzer I'll be using.

Thanks,

Brian

 

[(*steve*)]

That datasheet doesn't indicate that a lower voltage will work, but I presume you've tried it yourself.

What input signals will you use to set the voltage? Do you want to supply an equivalent voltage, or one of a couple of logic levels, or something else?

A simple solution is to apply a voltage to the base of an npn transistor, where the collector is connected to the +ve supply and the load is between the emitter and ground. The voltage applied to the base is approximately 0.6V higher than that applied to the load.

 

[bcavan]

Hi Steve, yes I tried it with lowering the voltage to about 3.3VDC and raising to 5VDC and it was clear the buzzer was louder at 5VDC. I have given more thought to using perhaps a PWM signal from the main controller. The main controller is a Windows 10 module (COMEX). My customer requested roughly four settings, High, Medium, Low and off. This gave me the idea of perhaps using a PWM signal from the comex module.

I did contact the buzzer manufacturer and they did advise that lower the voltage to the buzzer from 3.3VDC to 5VDC will work fine. As I mentioned in my post, the question is how to do that effectively.

 

[(*steve*)]

So, what signals do you have available?

PWM will need to be filtered or it will modulate the sound from the buzzer.

 

[bcavan]

I do have digital outputs available.

 

[(*steve*)]

If you set up an adjustable 3 terminal regulator, you could use a couple of digital outputs to turn on or off a couple of MOSFETs which select the resistor between the adj pin and ground. This would allow you to digitally select the voltage passed to the buzzer.

 

[Alec_t]

Here's an option for PWM control.
The blue trace represents PWM duty cycle.

 

[dorke]

This isn't a "simple buzzer".
It is classified as a "Medical Alarm",it has a full length tune and repetition rate.
You can hear the tune on this page.

In the application information (pages 9-10) it is explained how to get the 4 states you need "Off,Low,Mid,High", simple enough.

 

[Alec_t]

Aarghhh, I missed that . Good catch.
So, three digital outputs suitably driven, plus some 1A rated output transistors (BJT or MOSFET), plus a couple of diodes will do the trick, and PWM isn't suitable.

 

[(*steve*)]

From what I understood, the difference in behaviour desired is different from that obtained by asserting the different signals on the alarm itself.

 

[Audioguru]

Does a medical person need to learn the 20 melodies to determine the medical problem? They all sound like a buzzer. Why not have the device speak the medical problem in words like airplanes do? Pull Up- Terrain; Bank Angle; Stall etc.

 

[(*steve*)]

"RETARD RETARD". <-- Why is the aircraft calling me retard?

 

[Alec_t]

From what I understood, the difference in behaviour desired is different from that obtained by asserting the different signals on the alarm itself.

O.k. So PWM* could be used after all (per post #9), in combination with the mode selection (per post #11).

Edit: Filtered PWM.

 

[Audioguru]

You should not use PWM on the alarm, you can use filtered PWM to set the voltage of an LM317 voltage regulator.