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Magnetic reed switches for actuators

Glass reed switches are very fragile so please take note:

If you apply heat to the wire it will expand and shatter the glass. What you must do is to hold the wire near to the glass (but NOT touching the glass!) with a pair of "needle-nose" pliers. This will suck heat away from the wire before it reaches the wire in the glass. You can then use a very hot iron to quickly "tin" the end of the wire with solder.

Then tinned copper wire can be soldered to the reed switch wires, still using the pliers.

If you need to bend or shorten the reed switch wires you must again grip the wire close to the glass with pliers and bend or cut the wire furthest from the glass. The pliers will prevent any strain on the glass.

Once it's prepared, the reed switch can be glued in place using hot-melt adhesive or similar. If you use Evo-Stick DO NOT let it touch any connections because it corrodes.

Some Jacks use an encapsulated reed switch which is not soldered. The wires simply plug into tiny sockets. In this case it's simply a matter of holding each wire with pliers, bending it at right-angles then snipping off the excess length. Be very careful to ensure that the wire ends are the right distance apart so they fit in the sockets.

How to test a reed switch

Connect a multimeter to the reed switch with the lowest resistance (Ohms) range selected. The meter should indicate infinity. Now bring a magnet close to the reed switch. The meter should indicate zero Ohms as the switch reds click together. The orientation of the magnet is important. Hold it so that its North pole is close to one wire and its South pole is close to the other.

IMPORTANT

When you reconnect the dish motor, make sure that you have NOT connected the motor wires to the reed switch by mistake! If you do, then the instant the rotating magnet closes the contacts, the reed switch will explode or blow the fuse or both. You can protect the reed switch by connecting a very low current fuse in series with one of the wires connected to it. About 100mA should be fine.

For most reliable operation, the wires connecting the positioner equipment to the reed switch should be shielded to prevent electrical "noise spikes" from the motor from confusing the counting circuit inside the positioner.

Reed switches for fun and security

These handy devices are used with magnets to detect doors and windows opening. They can also be used for amusement in conjunction with electronic counters, lights, LEDs and other devices.

Approximate dimensions of glass envelope:
Length = 13mm
Diameter = 2mm

©2004 SatCure

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