Marchant Expanding Hoop
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| Switch type | Tactile |
|---|---|
| Sense method | Conductive |
| Keycap mount | Proprietary square peg |
| Switch mount | Communal top housing molded into case |
Marchant Expanding Hoop is a contact based switch found in Marchant 430 adding machines[1]. It consists of a communal top housing that is also part of the top case, a slider, a hoop spring (made by connecting either end of a long coil spring to form a hoop,) a masking ring, and the PCB. In the switch's resting state the diameter of the spring rests on the masking ring and cannot touch the PCB contacts. When you press the switch the tapered slider forces the hoop spring to expand such that it is no longer above the masking ring and instead is bridging the contacts on the PCB. When the switch is released the force of the hoop spring squeezes on the slider which, in combination with the tapering of the slider, provides return force and resets the slider. Because the slider passes through both a hole in a communal top housing and through a hole in the PCB the switches are remarkably stable, allowing for keys as wide as 2u to operate with no stabilization without experiencing any noticeable binding.
Keyboards
Marchant 430 adding machine
