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Subject: Re: a question on detecting open/close between 2 surfaces
Date: Thu, 21 Nov 2002 14:30:04 GMT
NNTP-Posting-Date: Thu, 21 Nov 2002 09:30:04 EST
Organization: Road Runner
> I am designing a circuit that requires the following switch (actually
> there will be about 30 of them):
> there are two surfaces (a hole and a cover) that are connected by a
> hinge. the two surfaces open and close. when closed, they form an
> airtight seal. The hole is about 1 inch in diameter.
> i wish to detect when the hole is closed (a "1" state), vs. open
> I've been looking for a small switch (maybe a pushbutton, but
> everything is too big) that I can mount at the bottom surface (the
> edge of the hole), so when the cover falls on it produces a signal.
> After thinking about it for a bit, I thought that maybe a hall sensor,
> or just two small conductive plates that when joined close the circuit
> and produce a voltage.
> Any ideas on either a good switch for this application, or conductive
> material that could be soldered on both hole and cover to give me the
> on/off signals?
> This is harder than I initially thought because of the space and cost
> limitations, but the need for a clear on/off signal.
> Hope this makes sense. I need to replicate this about 30 times so
> cost is an issue.
> Thanks in advance!
One way might be to use optical sensors. What you have not specified is
if something can in fact go between the two surfaces. Also, a hole is
not exactly a surface, now is it? Depending on overlap, if any, your
options will be more or less limited. If you need to know if the seal
has been formed, rather than just the cover touching the perimeter of
the hole, then perhaps pressure sensors are more suited. Cost may be
prohibitive here, but some sensors, if used properly, can be quite
effective at this with minimal cost. For instance, you may not care how
much pressure (or vacuum) there is, just whether there is indeed some
present. In this case, I might use piezo transducers. A circuit could
then look for a change in capacitance. This may not exactly give much
accuracy, but it can work. Also, you have not said if speed is an issue.
Some sensors will have a certain delay time before a change is seen on
the output. Although small, this delay can effect your design if these
covers are opening and closing at high enough speed.
I need more info to go any further here.