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Magnetic switch on PCB - how do they do it?

A recent round of scrounging for a Hall effect semiconductor led me to pry open a cheap magnetic burglar alarm. Instead of a semiconductor the alarm used a reed (?) switch mounted on the PCB.

(Is an open-air switch still considered a reed switch?)

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shows a picture of an old style magnetic switch on top with a picture of the cheap alarm below. The old style switch moves a good 1/8" between making and breaking. The new style switch shows no visible movement whatsoever to the naked eye.

How do they do that? Is automated parts placement accurate enough to manufacture a microscopic gap in the PCB reeds?

TIA.

-- Don Kuenz

Reply to
Don Kuenz
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"Don Kuenz"

** The term "reed switch" implies a glass encased one.
** Looks like a simple wire link ( near the magnet) in that PCB to me.

The thing is the TO92 pack has to be identified - it may well be a Hall switch IC.

The black blob looks like a ferrite cored inductor.

.... Phil

Reply to
Phil Allison

It's actually a switch. A VOM confirms that slight finger pressure breaks the connection.

AFAIK the rest of the circuit, including the S9014 small signal NPN, and the transformer (which looks like a coil in the picture) form a high amplitude oscillator to function as an alarm. (Two of the red leads in the lower picture connect to a piezoelectric device.)

-- Don Kuenz

Reply to
Don Kuenz

"Don Kuenz"

** Wild.

WFT not use a real, glass encased reed switch - their reliability is legendary.

If you have a problem with that device, then make the change yourself.

... Phil

Reply to
Phil Allison

Glass reed switches are standard for this use. Did some yahoo think they were too expensive to use?

Reply to
Greegor

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