hi,
i need a pressure sensor that will detect if someone leaves the bed. for example a bed bound patient sneaks out.
also, if available any example of of those circuit in the market...
any kind soul pls help...

 

Sounds like all what you are looking for could be easily done with an op amp and just a regular pressure sensor. You should be able to pick up the sensor from Motorola or Honeywell, but if memory serves me correctly they are pricey.

 

It's called a "load cell".

I have images of a patient with a bag of sand, trying to figure exactly how much to use, take out a pinch, then quickly swap himself with it, Indiana Jones-style.

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I thought what I'd do was I'd pretend I was one of those deaf-mutes.

 

Load-cells are expensive devices....and cumbersome to implement. The application is neither ratiometric nor quantitative.
A simple 'spring switch should justify the present necessity, However if one wants to be state-of-art, Several Peizo-Presure sensors are in vogue, at the present moment.

It is a simple excercise, I think, to fabricate a mechanical/electromechanical/electrostatic, Magnetostrictive, Inductive, Resistive, Photo=electric, Piezo-electric, .....and many more innovative/cheap alternatives (under the traditional 99c banner) to the suggested technological wonders (translate= expemsive).

I could elaborate if sufficient interest is expressed.....

 

You might try something where the bed leg meets the floor. This isn't perfect or foolproof but it's simple and could be implemented without modifying the bed. If the bed has 4 legs the weight of the bed is distributed over all 4 legs. The weight on each leg depends on where the patient is - but a given leg would carry some increased load at all times. You might fashion something with a fairly stiff spring and microswitch.

Another approach - some of the structural members in a bed deflect sufficiently to displace a microswitch.

Yet another approach - stick on strain gages on a structural member. With this you should be able to see the presence of a patient. You might also easily see fluctuations if the patient were to have a seizure.

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stevez

 

Some quite complicated suggestions so far.
I think a simple pressure mat, as is used at shop entrances to sound the customer entering alarm, is all that's required.
They could even be made from the conductive foam that IC's come packaged on. I had to make a smallish sensor to detect wether the head was lifted up while some leg exercises were done on a firm exercise couch surface. A bit of that foam sandwiched between brass shim disks did make a fairly reliable sensor.
Klaus

 

hi everyone,

thanks for all those whom reply..
i have decided to use flexiforce A201..
http://www.tekscan.com/flexiforce/flexiforce.html
are this pressure sensor suitable ?
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in the whole sensor circuit, they can be broken down into many portions...
however, i'm not very sure of the flow of the bloack diagram and if they are neccessary.

1.)w.bridge,

2.)amplifier,

3.)comparator,

4.)A to D converter,

5.)alarm,

6.)differential aplifier

7.)sensor,


thankyou....