Disable PIezo speaker

KJ6EAD

Joined Apr 30, 2011
1,581
How about just bypassing the whole oscillator while retaining processor control and monitoring? Disconnect the emitter of Q12, the anode of CR22 and the right end of R48. Put in a voltage divider made of 2 10k resistors between the node previously connected to Q12's emitter and 5V with the divider output connected to J1-8. I'd draw the modification but I can't download the schematic. You might have to change the divider ratio to get above 0.2V at J1-8 for all drive modes (3 processor outputs at J1-15, 17, 18).
 
Last edited:

Thread Starter

_Thoth_

Joined Apr 8, 2010
19
The piezo is sending back a 2.5 KHz signal to an amplifier and then on to the processor. So, now that this is far beyond me technically, is it possible to just build a circuit that would generate the 2.5 KHz signal from a 5V input ?

Again, very much appreciate the help.
 

KJ6EAD

Joined Apr 30, 2011
1,581
If you can give me the values of R34, R35, Q12 and L2 (56mH or 56μH or ?), I can try to create a 2.5kHz Colpitts oscillator around those components.

A good clear photo of that portion of the PCB would help.
 

KJ6EAD

Joined Apr 30, 2011
1,581
I assume it will, so any oscillator will have to be driven from the processor outputs as the existing piezo is.
 
Last edited:

KJ6EAD

Joined Apr 30, 2011
1,581
Put some hard drying epoxy in the hole then check if it dares to vibrate.
That's certainly a tempting and amusing notion. If you encapsulated the entire element enough to prevent an audible output, would it still deliver a 2.5kHz oscillation to the processor or does the piezoelectric effect require freedom of mechanical movement as the theory implies?
 

R!f@@

Joined Apr 2, 2009
9,918
OK ! I did not know a piezo uses 3 pins. The way I see it needs a supply to buzz and the other type which needs an oscillating voltage to vibrate.

So, how does the piezo puts back it's own vibration on to the supply line? And generate a signal. Never heard of tht type.
Besides a piezo is not used as a receiver when it is emmitting
 

CDRIVE

Joined Jul 1, 2008
2,219
Maybe I'm oversimplifying this but I think a Piezo element needs a sounding board medium to produce an appreciable audio dB level but it doesn't need this medium to resonate. If this is true then why not remove the element from the case and wrap it in foam rubber.? I would think any audio that could still be heard would be quite minimal.
 

Ron H

Joined Apr 14, 2005
7,063
That's certainly a tempting and amusing notion. If you encapsulated the entire element enough to prevent an audible output, would it still deliver a 2.5kHz oscillation to the processor or does the piezoelectric effect require freedom of mechanical movement as the theory implies?
As you suspected, it won't oscillate if it can't move.
 

KMoffett

Joined Dec 19, 2007
2,918
......
For reference the device is an intraveneous pump we are trying to silence for use on a film set.
Backing up a little...Have you contacted the pump manufacturer? If there's a positive atmosphere around the scenes that the pump will be shown in, their marketing people might be willing to help you. Product placement seems to be a big thing in film these days.

Ken
 

Thread Starter

_Thoth_

Joined Apr 8, 2010
19
Hello, yes the oscillation is required. If I touch the centre of the speaker to stop the beep I get an error. So definitely need to generate the 2.5 KHz back on the feedback line.

@KJ6EAD:

Do you need those values to build the circuit ? could it not just be a standalone circuit that takes the input voltage direct from the controller and then feed the oscillation back as if it were the speaker doing it ?
 

Thread Starter

_Thoth_

Joined Apr 8, 2010
19
No go on the product placement as they do not want to give me any details (I just think they do not know how to do it themselves) on how to silence the pump. Liability issues I guess, even though I explained that the pumps would never be, nor could they, used on a patient.
 

KJ6EAD

Joined Apr 30, 2011
1,581
Do you need those values to build the circuit ? could it not just be a standalone circuit that takes the input voltage direct from the controller and then feed the oscillation back as if it were the speaker doing it ?
It could be done either way but it would be simpler to use the existing circuitry as much as possible since it was designed to oscillate at the correct frequency already.
 

Ron H

Joined Apr 14, 2005
7,063
No go on the product placement as they do not want to give me any details (I just think they do not know how to do it themselves) on how to silence the pump. Liability issues I guess, even though I explained that the pumps would never be, nor could they, used on a patient.
Here is a little 555 astable that you could build on perf board. You might need a frequency counter (some multimeters have them) to calibrate it.
 

Attachments

Audioguru

Joined Dec 20, 2007
11,248
Your "piezo speaker" is not a speaker because it has a third wire which changes it into an oscillating beeper. It is connected to a transistor which has positive feedback from the third wire so it oscillates at a high frequency.

You can turn it off by disconnecting the supply voltage to the transistor or by shorting its base to ground with another transistor.
 

Thread Starter

_Thoth_

Joined Apr 8, 2010
19
You people absolutely rock ! We got it working this morning. I am glad I had my cohort with me though to notice, on the diagram provided, the 555 was labelled backwards. Used the pot to determine the value for R1 at 270K. Simply attached output to blue feedback wire and used existing red and black wires for ground and Vcc, the perfect solution.

It's been running for a few hours now without a single hiccup.

Please see attached for the finished circuit, which I hopefully drew correctly.
 

Attachments

Top