Hardware
========

The hardware is based upon an Arduino Due microcontroller, with a custom circuit board to interface
to the various instruments.

The circuit board is designed in `KiCad <https://www.kicad.org/>`__, source files are available
under the `hardware <https://gitlab.com/ptapping/trs-interface/-/tree/main/hardware>`__ tree of the
git repository. Gerber files suitable for production are also available in the `gerber
<https://gitlab.com/ptapping/trs-interface/-/tree/main/hardware/gerber>`__ directory.

The device connects to the laser sync input, optical chopper wheel input and output sync, delay
stage trigger and quadrature position inputs, and camera trigger output.

A combination of an inverting buffers and voltage divider networks convert the microcontroller's 3.3
V levels to the 5 V levels expected by the instruments. A balanced line receiver is used to
interface to the delay stage's quadrature position inputs.

The physical connections to the Arduino Due I/O pins are:

* Pin  2: Quadrature channel A (QA) in
* Pin  3: Chopper sync out
* Pin  4: Laser sync in (joined to pin 30)
* Pin  5: Camera trigger out
* Pin 10: (joined to pin 11)
* Pin 11: (joined to pin 10)
* Pin 13: Quadrature channel B (QB) in
* Pin 30: Laser sync in (joined to pin 4)
* Pin  6: Chopper sync in (any available pin, software defined)
* Pin  8: Delay trig in (any available, software defined)

Extensive use of the Arduino Due's timer/counter hardware is used, which mandates the purposes of
some specific pins.

.. figure:: images/trs-interface.png

    TRS-Interface circuit schematic.

.. figure:: images/trs-interface-3d.png

    Render of the TRS-Interface circuit board.

.. figure:: images/trs-interface-box.jpg

    The interface boxed up, connected to the other equipment and in use. The instrument below it is
    a Thorlabs BB201 brushless DC motor controller used to control the delay stage.