This might not even require a PIC.

Go to a department store and pick up one of those 'massage pillows.'  They
have some kind of pressure sensor in there to turn on the massage motor.
Should be easy enough to 'liberate' this sensor.  (And, as a bonus, you
could add a butt massage switch to your chair! <g>)

A simple 555 timer IC should be all you need to do the 1 minute timeout and
start the screamin' alert.

-Matt

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jean-Michel Howland
> Sent: Sunday, April 01, 2001 10:50 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE] Pressure/Mass sensor pad/mats
>
>
>  >> I need to to measure weight or to be more precise, measure if
> weight is
>  >> present or not in the rangeo of 0 to 100kgs.  I really need
> some sort of
>  >> flexible mat/pad that can be slipped under a cushion.
>  >
>  >
>  >With the intent of keeping it cheap and sensible I
>  >suggest buying a digital bathroom scales, quite common
>  >now, and they have all the hardware needed to measure
>  >weight in that range. You could interface to the PIC
>  >with little hassle.
>  >
>  >"slipping under a cushion" sounds difficult as it is
>  >hard to measure weight unless the person is stationary
>  >and above the sensor. If they are on a lounge or chair
>  >(you said cushion) they may have weight on their feet
>  >or arms.
>  >
>  >I'm sure if you explained more about the exact thing
>  >you want to achieve there would be some helpful answers.
>  >-Roman
>
> OK, good point about explaining more.
>
> Last night I had an accident in my electric wheelchair, I was driving
> around and ended up with my front in stuck in a drain hole, I
> fell forward,
> barely able to breathe and was stuck like that for 40 minutes.  I never
> want to go through that again so I need a solution.
>
> I thought of of 2 possible solutions:
>
> #1. Build some sort of pendant to wear around my neck that would contain a
> tilt sensor, RF transmitter and a timer.  However this would be bulky to
> wear because I couldn't build it small enough, battery life would be a
> problem and the range would be very small.  In my opinion this is
> not workable.
>
> #2. Slip a pressure transducer under my cushion and one behind my back,
> hook them into a PIC.  If I'm sitting in the chair the unit is activated,
> if I fall forward for more than a minute the PIC timesout and
> activates one
> of those 110db alerts which will be heard by the people around my
> house.  The advantage is everything can be mounted on and powered from the
> chair.
>
> The reason I want to find a mat/pad type of sensor is I'm reluctant to
> drill/cut or modify an $8000 chair that I don't own.
>
> Oh and before someone mentions the obvious, a seatbelt, well it's not an
> option. :o)
>
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