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Latching Reed Switch or Alternative?

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TwoPlank

New Member
I've been looking for a latching reed switch or some sort of alternative for a project of mine. I've searche the General Electronics Chat forum, but couldn't find an answer. I'm VERY new to electronics, but I'm trying to set up a simple circuit with a latching reed switch, miniature vibrating motor (pager motor), and a coin cell battery that will be sealed in an a capsule about the size of walnut shell. I've been experimenting with reed switches (form A?), but I need a switch that I can turn on and off (form E?). I've found a switch I think will work, but I'm not sure. It's made my Meder and it's part# MK6-4-E, but I haven't been able to find where I can purchase just a few of them, plus they cost a little more than I'm looking to spend. If there is an alternative to that part that someone can recommend or a simple setup that would work for my applicatoin, I would really appreciate it! Please let me know if you have any questions or need any additional information to help me come up with a solution.
 

MikeMl

Well-Known Member
Most Helpful Member
Are you trying to use the latching feature as a "zero power" memory?

A latching reed relay is just a glass-encapsulated reed switch which is "biased" by a permanent bar magnet. The coil is pulsed with one polarity where the magnetic flux adds to that from the magnet to latch the points closed, and the opposite polarity in the coil opposes the magnet to unlatch.
 

Ross Craney

New Member
but I need a switch that I can turn on and off (form E?).

You can get reed switches with changeover contacts if that is what you are looking for. They are easy to get & inexpensive.
 

Ross Craney

New Member
bluey - Jaycar (Australia) part # LA5070
$6.25 (aus$) each $4.95 for 10+ I use em all the time for customised electronic security applications
 

Mr RB

Well-Known Member
I would use 2 reed switches and an SCR (as Blueroom suggested). One reed turns it on, the other shorts the SCR causing it to turn off. That would be the most energy efficient setup since you wont have much energy reserve with a coin cell.
 

Ross Craney

New Member
There is a minimum "latching" current (anode to cathode) below which the SCR will not stay latched. He may need to choose his SCR very carefully.
 

Mr RB

Well-Known Member
Agreed. :)

C106D, TO126, Ion=0.2mA, Ihold=5mA
C103B, TO92, Ion=0.2mA, Ihold=5mA

Both are common enough. However the forward voltage may be too high, I'm thinking he might need 2 coin cells. That might still fit.

Here's an off the wall thought, what about an inertially operated switch? Get a miniature toggle switch, epoxy a lead sinker to the end of the lever and glue it in the waterproof capsule with battery and motor. A harsh impact would flip the switch either on or off, depending which way you impact it. ;)
 

floyd955

New Member
Latching Reed Switches

There are latching reed switchs out there in the SPDT configuration.
How much current are you talking about and what is the switching frequency of the circuit you are trying to control.
Look at Hermetic Switch Inc. Model HSR-638BSL Form C Bi-Stable Latcher.
 
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