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'[ot]: thermostat switches???'
2000\12\14@225109 by rad0

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Hello Picsters!

I want to make a gadget using a switch like the
ones used inside a house thermostat, the kind that have
mercury inside, and I was wondering what these switches
are called, I looked for them in digikey and couldn't find them?

Secondly, I don't need temperature sensing, I am just trying
to determine when a door is opened,  a vertical door, with
hinges on the bottom, vertical when closed, horizontal when opened,
I suppose I could just rig up some sort of ball to hit a micro-switch,
but I was wondering if there is something like this ready made?

The thermostat thing comes to mind, but maybe there is something
cheaper, better, faster, etc..

Thanks

Rick

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2000\12\14@231225 by Stephen B Webb

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> to determine when a door is opened,  a vertical door, with
> hinges on the bottom, vertical when closed, horizontal when opened,

Radio shack sells these "mercury switches" for about $3 each IIRC.

Radio shack also sells burlgar alarm switches for relatively cheap.  My
understanding is that there are two pieces, a magnet and a switch.  The
switch is closed when the magnet is in close proximity.  I'm not sure how
much gravity affects the switch (ie if these switches are normally used on
"normal" doors, and mounting it on the door you describe (sounds sort of
like a cellar door to me) might take  a different switch or  different
mounting approach)

I was thinking about doing something like this on my car trunk.  Too many
projects..

-Steve

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2000\12\15@012058 by Peter May

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Mercury Tilt Switch or what about a reed switch and magnet?

-----Original Message-----
From: pic microcontroller discussion list
[spam_OUTPICLISTTakeThisOuTspamMITVMA.MIT.EDU]On Behalf Of rad0
Sent: Friday, 15 December 2000 2:52
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject: [ot]: thermostat switches???


Hello Picsters!

I want to make a gadget using a switch like the
ones used inside a house thermostat, the kind that have
mercury inside, and I was wondering what these switches
are called, I looked for them in digikey and couldn't find them?

Secondly, I don't need temperature sensing, I am just trying
to determine when a door is opened,  a vertical door, with
hinges on the bottom, vertical when closed, horizontal when opened,
I suppose I could just rig up some sort of ball to hit a micro-switch,
but I was wondering if there is something like this ready made?

The thermostat thing comes to mind, but maybe there is something
cheaper, better, faster, etc..

Thanks

Rick

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2000\12\15@033821 by Roman Black

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Stephen B Webb wrote:
>
> > to determine when a door is opened,  a vertical door, with
> > hinges on the bottom, vertical when closed, horizontal when opened,
>
> Radio shack sells these "mercury switches" for about $3 each IIRC.
>
> Radio shack also sells burlgar alarm switches for relatively cheap.  My
> understanding is that there are two pieces, a magnet and a switch.  The
> switch is closed when the magnet is in close proximity.  I'm not sure how
> much gravity affects the switch (ie if these switches are normally used on
> "normal" doors, and mounting it on the door you describe (sounds sort of
> like a cellar door to me) might take  a different switch or  different
> mounting approach)


Make sure to run the mercury switches at very low currents.
At anything over a few mA they "arc" at the pins that contact
the mercury, and soon form corrosion that gives bad conductivity.
Once corroded you can just throw them away! I have used these
for years in motorcycle tilt alarms and stuff.

The smallest current the better, under 1mA best.
-Roman

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2000\12\15@095821 by todd + jean

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Roman Black wrote:
>Make sure to run the mercury switches at very low currents.

Could this be caused by running the switches on direct current? mercury
switches are used in the common household light switches and are rated
at 20 amps  120 volts A.C.

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2000\12\15@105221 by Roman Black

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todd + jean wrote:
>
> Roman Black wrote:
> >Make sure to run the mercury switches at very low currents.
>
> Could this be caused by running the switches on direct current? mercury
> switches are used in the common household light switches and are rated
> at 20 amps  120 volts A.C.

I have never heard of this! In light switches?? Australia is a 240v
country, this seems almost insane to me. The mercury switches I have
seen and used for years are the typical cheap ones sold as "tilt"
switches in hobby electronics shops. Probably due to the metal
composition of the two prongs, they don't like high currents.
Maybe your light switches have special metal as the prongs, I
would really like to see one of these switches! :o)
-Roman

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2000\12\15@110135 by David Kott

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> todd + jean wrote:
> >
> > Roman Black wrote:
> > >Make sure to run the mercury switches at very low currents.
> >
> > Could this be caused by running the switches on direct current? mercury
> > switches are used in the common household light switches and are rated
> > at 20 amps  120 volts A.C.
>
> I have never heard of this! In light switches?? Australia is a 240v
> country, this seems almost insane to me. The mercury switches I have
> seen and used for years are the typical cheap ones sold as "tilt"
> switches in hobby electronics shops. Probably due to the metal
> composition of the two prongs, they don't like high currents.
> Maybe your light switches have special metal as the prongs, I
> would really like to see one of these switches! :o)

Nope.. it's true.  These switches are quiet.  No contact closures, so there
is no appreciable sound when you make or break them.

I don't presume he's talking about Mercury Whetted contacts, a la' relay
style.  I do believe that he is genuinely referring to the Mercury
sustaining the full current load of a home appliance/light/whatnot.

-d

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2000\12\18@090413 by Alan B. Pearce

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>I suppose I could just rig up some sort of ball to hit a micro-switch,
>but I was wondering if there is something like this ready made?

>The thermostat thing comes to mind, but maybe there is something
>cheaper, better, faster, etc..

I have found mercury tilt switches in the handsets of telephones where the
handset had to laid on its back if using it as a speaker phone. If the handset
was placed microphone down (as it is in the cradle) the tilt switch shorted out
the microphone so you could turn on the speaker with the handset still in place
to dial a number. This stopped the audio feedback loop while the handset was in
the cradle.

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