We need to force into oscillation a small card (50 gr) hanging from a wire.

After evaluating all acceptable means (for us) we found that blowing a tiny jet of air from time to time will do.

Without resorting to microblowers, we DO know they exist, (expensive and hard to get locallly), would you suggest something else to obtain a gentle air blow lasting for less than one second every time is needed?

Please note we are not looking for other solutions; just to generate a gentle, very quiet, air blow.

Mechanical noise is a no no and air volume required is definitely SMALL.

 

What about a piston-like solution, move a large surface enclosed in some space with a hole of the right size to make the right blow. For example a speaker ramped to full excursion and then back, in a smooth but fast fashion so that is reasonably quiet.

 

Gracias for replying. A "silent" speaker"?

Speaker suggests sound so, why not noise?

In doubt...

 

There used to be a toy called the Wham-o Air Blaster that worked this way.

http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=1334

As I remember, it was fairly quiet,too, making sort of a "thud" sound. I think that it has an internal diaphragm that was pulled back, then released, to propel a single blast of air an amazing distance. It could extinguish a candle at 20 feet.

I would also agree that a speaker inside a housing like the Wham-o air blaster might work, and may be quiet enough if the current is carefully ramped up, then down,
to result in a single puff of air from the nozzle.

 

I'd think something like a small solenoid plus a plastic bag.

Anchor the center of one side of the bag to a surface with the whole thing surrounded by a light frame such as a flattish box.

Tape the end of the bag up, with just a tube connected in to it.

put a 'bridge' across the box & bag with a solenoid in the middle, the moving part attached to the center of the top surface of the bag.

Use a solenoid with a spring return (normally up) so actuating the solenoid pushes the top surface of the bag down and it acts like a bellows. For a solenoid with no spring, turn the thing over so it falls/opens by gravity.

You could possibly use a relay with the cover removed and an extra wire arm attached to operate the bellows, rather than a solenoid.

The damping caused by moving the plastic & air should give a slow, smooth action. You could add a thin shim of plastic or foam in the solenoid if it clicks at the end of it's travel.

You could also stand the whole frame on edge if it works better with the relay or small solenoid, so it's not fighting gravity.

 

A slight variant on the idea described by rjenkins would be to substitute the relay with a small motor with a metal disk mounted on the shaft. Then you attach the link from the diaphram to a point on the metal disk. Then the speed of the motor would modulate the diaphram at a controllable rate. The rate could be set to be subsonic to preclude noise from the motor or the moving air.

hgmjr

 

or use a fish tank air pump..... simple, easy to acquire, if you spend a little extra you can get a really quiet one....

B. Morse

 

Hi Agustín.
Use Nitinol - the muscle wire to move in a fanning way forth and back (abanico), or if you prefer, to push/pull the hanger string. No sound at all, and as much action as needed.