There exist two kinds (AFAIK) of these:
- mechanical ones
- and optical ones.
There are many variations of these:
- with built-in push button
- with built-in push/pull switch (for Airbus builders)
- concentric rotaries (stacked, the axis has an outer and inner part)
- these can be combined with switches as well
- usually two rotaries stacked, but sometimes more
just about any Microchip PIC can be used to decode 2 bit gray quadrature code. You need two inputs for each, and two outputs (up and down). Alternatively, you could use a different software that eg. uses the I2C protocol to tell the master (eg. PHCC motherboard) which rotaries where turned, and in which direction.
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