Instructables

Step 22: ATTACH THE REED SWITCHES

Picture of ATTACH THE REED SWITCHES
sensitivitychart.jpg
spacebarreedswitch.jpg
Experiment With Positioning
Unless you have worked with reed switches before, it may be tricky to find the appropriate place to attach them to your typewriter.  So, some experimentation with a multimeter is required before finalizing the position of each reed switch.  First, attach a magnet to the key you wish to detect (for example, the spacebar, backspace key, shift key, or return carriage lever).  Next, attach the probes of your multimeter to the wires of the reed switch, and use the "continuity" setting (often signified by a little beeping sound wave) to monitor whether the reed switch is open or closed (see picture above).  The multimeter will emit a beeping noise whenever the switch is closed (i.e. when a magnet is nearby).

HINT: The reed switch can detect magnets in any direction, but it is most sensitive to magnets that are directly in front of it or behind it (see 2nd picture above).

Finalize the Position
When you are satisfied that you have found a good position for the reed switch, so that it opens and closes consistently whenever the key is pressed, use superglue to attach it permanently to the chassis of the typewriter.  I like to use hot glue as well -- not to attach the reed switch but to tack the wires down.

Example -- Space Bar
In the example shown above (see 3rd picture), the switch is normally open, but closes whenever the space-bar is pressed.  However, you may decide to use the opposite configuration -- so that the switch is normally closed but opens when the key is pressed.  It makes no difference whether the switch is normally open or normally closed, because the software is able to figure this out during calibration.
 
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d_septikhan2 years ago
Also, orientation of the magnet is also important.
http://www.kjmagnetics.com/blog.asp?p=reed-switches-and-hall-effect-sensors