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Help with a component/idea

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ankurchanga

New Member
I am a really newbie to electronics but need some desparate advice.

I need to create a little circuit that is triggered by a sensor - the sensor needs to be variable according to how much pressure is to be applied ?

Can anybody advise me as to the simplest/best thing to use for the job.

Thanks.
 
i am new to electronics but i think i read somewhere that there is some sort of crystal that will put out electrical pulses or something if there is pressure along different axes
 

kinjalgp

Active Member
You can make use of a Load-Cell which is used in weighing machines. Its is a resistive transducer whose resistance varies depending on pressure applied.
 

bogdanfirst

New Member
yes, a quartz cristal gives out pusles when it is squeezed, never tried it, but i dont think that it is that hard to build a simple device to do that.
i am not talking about the quartz cristals used in oscilators, i am thinking to get a piece of high purity quartz from the nature, from a rock.
i dont know how to do it, maybe put it between 2 sheets of metal.
 

kinjalgp

Active Member
Its difficult to make good contact between metal sheets and quartz since it is not solderable.
 

bogdanfirst

New Member
that's what i was thinking of, but you cant solder everything...
i once saw a guy that build some quartz generators and put them on his shoes and used the energy generated to charge his cell phone....
 

Mosfet

New Member
the foam used to protect integrated circuits from static charge is slightly conductive - pressure on the foam lowers it's resistance - not sure what you want to trigger
 

john1

Active Member
Hi ankurchanga,

I need to create a little circuit that is triggered by a sensor

The simplest sensor arrangement that comes to mind
is a micro-switch.

the sensor needs to be variable according to how much pressure is to be applied ?

Well, if is just mechanical pressure, like someone
treading on it, then some sort of lever mechanism
would do, maybe with an adjustable screw to set the
operation at a suitable weight.

But if its hydraulic pressure or air (gas) pressure
from about 5 PSI to about 50 PSI then i would suggest
getting the COLDNESS sensor out of an old fridge.
I mean the bit where the temperature control is, its
usually just inside the door.
They usually have a little bellows working a micro-
switch.
Its a cold sensor, but it works by pressure on the
bellows at this point.
Pressure adjustment would be done with the TEMP
control.
Cut off the copper tubing and fix the test pressure
to it, see if the range is what you need.

If its low pressure air (gas) below five PSI then
get a water level sensor from an old washing machine,
you may have to look at a few types, they dont all
use a DIAPHRAGM but most of them do.
Again is just the pressure that works the diaphragm
and operates the switch, but get the whole unit cos
the switches they pick operate at low pressures an
ordinary micro switch would be too stiff.

If none of these are suitable,
then come back with more information as to the use.

Regards, John
 

john1

Active Member
Mosfet,

Thanks for that info on the anti static foam,
that might do just what i want,
for something else.

Regards, John
 

Scubasteve

New Member
I've heard of using two plates separated by a thin peice of foam to vary the capacitance, which you can use in a LC tank circuit through a frequency to voltage converter. This might be one of the most robust ways to do it without having to make any orders, but it does take some knowhow.

You need to explain your application more. You can be talking about 1oz-1000lbs of working pressure that you want to keep a linear range of. How linear do you want this range to be? What kind of output do you want? I know that you know what you want, just communicate it to us effectively and we should be able to help!

Steve
 

pebe

Member
bogdanfirst said:
piezo buzzers change the characteristics if you put pressure on them, you cold use them too......
The equivalent circuit of most piezo stuff when used in that mode, is a generator in series with approx a 1nF capacitor.

They need a gentle tap or similar which will produce a sharp transient so that the sharp leading edge gets past the 1nF. I doubt they will respond to a steady pressure unless the load they are looking into is very high ohms.
 

Mosfet

New Member
A junked automobile engine could have several free vacuum/pressure sensors. Usually these are resistive bridge circuits that have two electrical connections and a mechanical air connection. Make sure there is no petroleum reside and measure the resistance on the two leads while you 'blow' or 'suck'. Add an opamp and you have a voltage that varies per pressure.

Autos also have on/off pressure switches that come in handy.

If air pressure doesn't affect the sensor, maybe it's a temperature sensor. Keep that around for another day.
 

ankurchanga

New Member
Thanks

Thanks for all your lp so far.

but i think i need to give you more info: i want a sensor that will give a variable signal out when very light pressure is applied...imagine for exaple you baned your palm on a table, i want the sensor to be placed on the heel of your hand and give me a variable signal depending on how hard you hit the table - so not a ver heavy duty component ? see what i mean ?
 

bogdanfirst

New Member
you are right Pebe. they only respond in changes of pressure, not when you have a constant pressure.
but it depends on what pressure you need, air, water, or the pressure generaten by stepping on something or placing an object on the sensor....
i build some sort of pressure sensor wich can be adapted...i hope so...
i used an old tv potenriometer(from a WB tv) and connected a spring on it, but it wasnt accurate....
you remember the big old microphones that used carbon ? you can use on of these.....
 

Mosfet

New Member
A small air bladder attached to a glove.
Connect the bladder to an electric auto tire pressure guage.
I have seen these guages at Kmart for less than $10.
Miniture microprocessor-controlled digital readout pressure sensor.
 

bogdanfirst

New Member
meybe yo can trey something like this?
 

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ankurchanga

New Member
Thanks - not convnices

Thanks guys but still doesnt feel right. There is goingto be one of these on each finger and on the heel of the hand it has to be quite small, an air bladder is an interestin idea but will be too big..these things need to be the size of microswitches - doesnt have to be sensitive just has to be able to have 1-3 possible readings, as opposed to a microswitch that will have only one - any ideas ? sorry to wrack your brains...
 
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