Steve Nordhauser wrote

> I am developing an underwater digital camcorder and need some suggestions
> on pushbutton switches for the body.  The requirements are that they are
fairly
> small (1/4" to 1/2"), sealed to 200ft, can handle harsh environments (sand
and
> sea water) and provide contact as long as depressed (unlike piezos which
put
> out a single pulse).  They should not draw much current when open and can
be
> read by a PIC.  One of the hangups is that at 200ft, the pressure on a
1/4"
> button is 4.4lbs.  At sealevel, the switch would need at least 5lbs of
force on
> the button to remain useful at 200ft.
>
> We are considering resistive ink technologies and looking for the pressure
> differential of someone adding 1 lb of force.  Any other creative ideas
would be
> greatly appreciated.  Sorry if this is somewhat off topic.  This is a
great assembly
> of creative people (and I am using a PIC to read them.....)
>
> --
Use a Reed Switch (or even a reed relay) on the inside of the pressure
casing with a bar magnet on the outside. When the bar magnet is in line with
the reed, the circuit will be closed. If the centre of the bar magnet and
the centre of the reed are aligned then when you pivot the bar magnet
through 90 degrees the magnetic field across the reed will drop to zero and
the reed contacts will open circuit. Simple, Cheap, no seals or pressure
differentials to worry about and it draws no power.

Regards
Chris

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