[MakeLV] Replacement magnetic reed switch for bike computer?

[rsjames at ix.netcom.com]

Generally, reed switches are pretty interchangable, especially for low power applications like bike computers. The "Shack" used to sell bare switches.  I don't know if they still have them.  You could probably use one from a door or window alarm.  They may sell just the switch and matching magnet for expanding alarm systems.  Just look for one that has a rectangular box about an inch and a half long and about 3/8 inch square.  Also check to make sure that the reed switch isn't potted in the box (filled with epoxy). 
R. S. James    

-----Original Message-----
>From: Randy Kramer <rhkramer at gmail.com>
>Sent: Mar 23, 2012 1:13 PM
>To: Build things for fun! <makelehighvalley at makelehighvalley.com>
>Subject: [MakeLV] Replacement magnetic reed switch for bike computer?
>
>Has anyone here ever picked out a magnetic reed switch to use as a replacement 
>for a bike computer (i.e., electronic bike speedometer / odometer ...)?
>
>We have two bike computers that are non-working because the reed switches have 
>died.  (Both due to impact, they no longer switch, they're stuck in one 
>position.  I've tried tapping them fairly hard to get them to operate again, 
>but no luck.)
>
>I'd like to buy an off the shelf reed switch and solder it in place of the 
>original.
>
>If anybody has done that, do you have a reed switch you'd recommend?
>
>If not, I did a little bit of looking.  The reed switch in one of the speed 
>sensors is about 1/2" long.  I found a reed switch that is 1/10" (diameter) 
>by about 1/2", so it should physically fit.
>
>Here is the switch I found:
>
>SWITCH,MAG REED,SPST-NO 0.5A at 100VDC. JAMECO VALUEPRO MKA-14103-1015-R
> 
>http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_171872_-1
>
>and a link to the data sheet:
>
>http://www.jameco.com/Jameco/Products/ProdDS/171872.pdf
>
>I can't copy and paste from that .pdf, so I'll mention a few things:
>
>The battery operating the computer is (depending on the computer) either a 3.2 
>or 1.6 volt button cell. (2032 or 2016).  Thus, I'm sure the voltage at the 
>reed switch is no higher than that (it could be, I haven't measured it, but I 
>doubt it is any higher).  So, I need contacts with low contact resistance.
>
>I don't need high current capability.
>
>I do want good resistance to mechanical shock.  This one is rated to withstand 
>1 msec. shocks of up to 150 g, and sinusoidal vibration of 1 to 2000 Hz. at 
>20 g.  Sounds likely to be tough enough.
>
>Any comments, other suggestions?
>
>Thanks!
>Randy Kramer
>
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