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### Topic: Driving a piezo loudly! (Read 7034 times)previous topic - next topic

#### jremington

#30
##### Jun 12, 2018, 07:19 pm
You will destroy the transistor (and may already have) if you fail to use a base resistor (1K - 10K).

To what peak-to-peak voltage have you set the signal generator?

Quote
however it seems like i only get power from the transistor-gate and nothing form the actual DC power source.
Please explain why you think this.

#### pwillard

#31
##### Jun 12, 2018, 07:23 pm
Note:  I'm indicating you have to drive the BASE of the transistor with a PWM signal.  No switching... no voltage...   Just feeding DC won't do anything.

#### allanhurst

#32
##### Jun 12, 2018, 07:30 pmLast Edit: Jun 12, 2018, 07:40 pm by allanhurst

You probably don't need the output capacitor - replace it with a short.

You won't get anything from your circuit as there's no way for the transistor to get power...

A capacitor ( such as a piezo) blocks dc current flow.

Allan

#### jremington

#33
##### Jun 12, 2018, 07:52 pmLast Edit: Jun 12, 2018, 08:01 pm by jremington
If you want to simulate a piezo element, you need to take into account its equivalent inductance, which can be surprisingly large, as well as the internal resistance. At the moment, you are just (incorrectly) simulating an LCR circuit.

Unfortunately decent SPICE/LTSPICE models for a piezo element are hard to find, but here is one attempt.

#34

#### Danielvt

#35
##### Jun 12, 2018, 08:01 pm
I just thought the other thread went a bit off-topic in regards to the original post, which is why i made a new post :-)

#### Danielvt

#36
##### Jun 12, 2018, 08:10 pm
Where's the (simulated) meter connected?    Of course the important thing is the voltage across the piezo.

Is the capacitor supposed to be the Piezo or is it supposed to be the resistor?

Of course, if you can supply a higher DC voltage in the real world you wouldn't have to be playing-around with resonant circuits.

The voltage is measured at the capacitor - which is yes supposed to act as the piezo. I don't have the possibility of having a higher DC-voltage across the piezo since we're running on a 3v battery - which is why i'm using a LC-circuit

#37

#### Danielvt

#38
##### Jun 12, 2018, 08:47 pm
You will destroy the transistor (and may already have) if you fail to use a base resistor (1K - 10K).

To what peak-to-peak voltage have you set the signal generator?
Please explain why you think this.
I run the signal generator at 1.5V but if i change it, the output changes (and doesn't change if i change the DC input!) which is why i think the signal is providing the output.

jremington i have it working perfectly without the transistor, so my ressonant LC circuit is working fine

Note:  I'm indicating you have to drive the BASE of the transistor with a PWM signal.  No switching... no voltage...   Just feeding DC won't do anything.

I'm not really sure what you mean - how should i simulate it? Could you elaborate?

Thanks for all your responses! Appreciate it!

/ Daniel

#### Danielvt

#39
##### Jun 12, 2018, 08:55 pm

You probably don't need the output capacitor - replace it with a short.

You won't get anything from your circuit as there's no way for the transistor to get power...

A capacitor ( such as a piezo) blocks dc current flow.

Allan
Hi Allan,

I tried the circuit with no luck (see attached schematics)

#### jremington

#40
##### Jun 12, 2018, 09:52 pmLast Edit: Jun 12, 2018, 09:55 pm by jremington
Quote
I tried the circuit with no luck
You tried a different circuit, which won't work for several reasons.

You could try the one in reply #22, carefully following the instructions to replace the speaker (8 Ohm R2) with the piezo, but it won't be any louder than the direct output from an Arduino, because there is no voltage boost.

#### allanhurst

#41
##### Jun 13, 2018, 12:21 amLast Edit: Jun 13, 2018, 12:49 am by allanhurst
jremington - you're right of course.

1/ modelling a piezo as a series capacitor and resistor isn't very accurate , but it's a reasonable starting approximation. A better model will not be linear, but will vary strongly with excitation voltage.
Can't be bothered.

2/ my crude circuit does not, as you say, provide any voltage gain, but it will provide much more current, which may be useful driving a low impedance series resonant load.The series l-c provides the voltage gain at resonance.

Pwillard : your circuit is a basic boost voltage convertor  - but we don't want high voltage dc.

Danielvt. Your implementation of my circuit is inaccurate. Get it right and try again.

1 resistor, two transistors. Omit the 100uF capacitor. Could anything be much easier?

Allan

#### Wawa

#42
##### Jun 13, 2018, 08:38 am
Didn't read all the posts in this thread, but isn't it easier to use a MAX232 to drive a piezo.
Like the do on an HC-SR4 ultrasonic sensor module.
The MAX232 should be able to drive a piezo to ~30volt peak/peak.
Leo..

#### Danielvt

#43
##### Jun 13, 2018, 09:25 am
Didn't read all the posts in this thread, but isn't it easier to use a MAX232 to drive a piezo.
Like the do on an HC-SR4 ultrasonic sensor module.
The MAX232 should be able to drive a piezo to ~30volt peak/peak.
Leo..
Hi Leo!,  thanks! I can't find any resources on how to wire/set up the Max232 to a piezo, could you elaborate? I believe 30vPP from a 3.3v source sounds amazing though! :-)

/ Daniel

#44