Door knob switch for wrist supination and pronation excercise

Requested Project

A low voltage switch operated by twisting a door knob to be used as a training device for people who have difficulty with wrist supination and pronation (rotation of the wrist).

Design Notes

The door knob switch is a training device for people who have difficulty with wrist supination and pronation (rotation of the wrist).  A micro switch is attached to the door knob so that rotation of the door knob will trigger the switch.  The switch is attached to an 1/8 inch phone plug that can be plugged into actuation devices in the class room.

One half of a door knob is mounted on a base.  The cam action of the door knob shaft triggers a micro switch mounted inside the base.  The base consists of three sandwiched plywood boards with the micro switch mounted inside a hole in the center board.

There are many types of door knob mechanisms.  Switch construction must be adapted accordingly.  The design described here uses a door knob with a square shaft that rotates with the door knob and the spring return is contained in the door knob.  Switches have also been built with door knobs that output a linear motion instead of the rotating shaft type described here.  Construction is similar for all door knob types, however the location of the micro switch must be appropriate for the type of door knob used.

The cam action of the shaft in the door knob is used to trigger a micro switch.  A Radio Shack submini lever switch was used.  This door knob has a square shaft that is used as the cam.  A spring return is built into the door knob.  The base consists of 1/2 inch plywood (5.5" x 7") with a 2 inch hole to mount the door knob.  A grove is cut in the bottom of the 1/2 inch plywood for the cable.  The bottom of the base is a 1/4 inch plywood.  A blind hole for the door knob shaft is drilled in the bottom plywood and two door knob mounting holes are drilled through the bottom plywood.  A small sheet metal piece is sandwiched between the two sheets of plywood to create a stable bearing surface for the door knob shaft and micro switch mounting as shown in the picture below.

Adjustment of the micro switch is critical.  Final adjustments can be made by bending the lever arm of the micro switch.  The lever arm must be adjusted to be tangent to the cam at the point of contact.

RCRV designer is John Wauer, and was requested by GWAEA. The project was begun May 9, 2001 and completed May 9, 2001.


Additional Information:

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Construction drawings

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