Magnetic Switch?

[Technology Guy]

Is there such a thing as a magnetic switch or sensor that would sense
a magnet in the range of 12"-6" away?

 

[Gareth Magennis]

Look for Hall Effect sensors - 3 pin devices that either switch or give a
variable output in the presence of a magnetic field. The maximum range is
dependent on the srtrength of the magnet and the sensitivity of the device.
The variable output ones could be used in a comparator type circuit to give
greater maximum range than the fixed types.


Gareth.

 

[Dave VanHorn]

Reed switches can do this, but it's not easy.

You add a biasing magnet that brings it almost to the switch point.

You can also detect by pulsing a solenoid coil around the switch, till the
switch closes.
The on-time then tells you the strength and direction of the external field.
If it takes longer, the external field is opposing, shorter means it's
aiding.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Is there such a thing as a magnetic switch or sensor that would sense
a magnet in the range of 12"-6" away?

It's called a compass.

Seriously. I've seen this with a set of foil plates glued to the
compass' glass face. The plates are part of a capacitive bridge. As
the needle moves, it unbalances the bridge. A similar arrangement can
also be used with a bubble level.

If you want to find out more about these kinds of sensors, try looking
for info on geotechnical stuff like earthquake and tilt sensors; and
also check the Amateur Scientist articles in Scientific American.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

Reed switches can do this, but it's not easy.

You add a biasing magnet that brings it almost to the switch point.

You can also detect by pulsing a solenoid coil around the switch, till the
switch closes.
The on-time then tells you the strength and direction of the external field.
If it takes longer, the external field is opposing, shorter means it's
aiding.

This kind of reminds me of the flux gate magnetometers.

 

[Dave VanHorn]

This kind of reminds me of the flux gate magnetometers.

Kinda..

I did this years ago, as a demo of what a determined person could easily do
to defeat an alarm system. I built this, and some other goodies into a TV
remote case. This part was for locating magnetic switches in doors.

It also looked for IR beams, and ultrasonics, and some other things.