Merge pull request #932 from TheDeanLab/updated_shutter_documentation

Update Shutter Website Page

Author: AdvancedImagingUTSW

docs/source/user_guide/hardware/shutter.rst

@@ -2,19 +2,36 @@
 Shutters
 ========
 
-When controlled with analog, digital, or mixed modulation, not all laser sources
-reduce their emitted intensity to 0. In such cases, residual illumination subjects
+When only controlled with analog modulation, many laser sources do not
+reduce their emitted intensity to 0 watts. In such cases, residual illumination subjects
 the specimen to unnecessary irradiation between image acquisitions. Shutters overcome
 this by completely blocking the laser, albeit on a much slower timescale than direct
 modulation of the laser. With **navigate**, shutters automatically open at the start
 of acquisition and close upon finish.
 
+Most shutters are controlled via a digital voltage. When the voltage is high (e.g., >
+2.5 V), the shutter is open, and when the voltage is low (e.g., < 2.5 V), the shutter
+is closed.
+
 ------------
 
-Analog/Digital-Controlled Shutters
-----------------------------------
+National Instruments (NI)
+----------------------------
+
+We can control these shutters using a digital output from a National
+Instruments (NI) data acquisition card.
+
+.. Note::
 
-Thorlabs shutters are controlled via a digital on off voltage.
+    If the shutter opens and closes immediately upon starting an acquisition, try a
+    different port for the digital I/O on the NI data acquisition card. Some NI devices
+    (e.g.PCIe-6738) have port/sample size limitations. If the port/sample size is
+    exceeded, the shutter will not open. For example, on our `NI PCIe-6738 <https://www
+    .ni.com/docs/en-US/bundle/pcie-6738-specs/page/specs.html>`_ using port 0 for the
+    shutter causes this issue, but switching the shutter to any port 1 channel fixed it.
+    In comparison, for the `NI PCIe-6259 <https://www.ni
+    .com/docs/en-US/bundle/pci-pcie-pxi-pxie-usb-6259-specs/page/specs.html>`_,
+    using port 0 had no averse effects.
 
 .. collapse:: Configuration File