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'[EE]: Tilt switch replacement BEWARE'
2001\06\28@094932 by Lawrence Lile

Oh, Peter, beware the pitfalls of ball switches, for they are many.  I
design steam irons, and they need tilt switches.  We got away from mercury
switches a couple of years ago, because of the haz waste issue.

We buy a ball switch from

COMUS INT'L part number CW1300-1

Now, many here have suggested a homemade ball switch consisting of a metal
ball in a cage.  DON"T DO THIS if you are going into production.  These
types of switches WILL fail.  It takes only a tiny piece of dust or a tiny
spot of corrosion to disable them.  Your fingerprint on a steel ball will
eventually corrode just enough to render this switch useless.  Probably
during your warrantee period.

I've tested dozens of ball switches.  Many of them will operate OK about 90%
of the time.  My simple test is this:  Apply an ohmmmeter to the terminals,
and hold the switch so it's contacts are open.  Then very very slowly tilt
it until the contacts should be closed.  Any mercury switch will pass this
test every time.  MOST commercial ball switches will fail one time in ten!
No kidding!

If you don't care about a 10% failure rate, then go ahead and use a homemade
ball-in-cage or a cheap commercial ball switch.  The one mentioned above is
about US$0.15 in quantity, maybe 3mm diameter, 5mm long.  Comus makes dozens
of others, and will custom make one for your app if it is production.  They
make them in clean rooms, with silver plated balls and silver plated
contacts.  You can buy a knockoff switch for US0.10 that is not made in a
clean room and will fail.

I've got maybe 100,000 of these switches out in the field now, no problems
with them.

-- Lawrence Lile

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