The working principle of the optocouplers is quite simple: A photo-emitting
element - usually a LED, is encapsulated inside the die along with the photo-
sensitive element, which can be a photo-sensitive transistor or a photo-
diode. LEDs and photo-sensing elements are galvanically isolated, making
the input and output electrical networks completely independent of each
other. When the LED is biased, it emits light which in return causes the
current to flow through the photo-sensitive element. In these particular
optocouplers, the output stage is additionally conditioned by a Schmitt
trigger and it drives the output transistors which form a totem pole output
stage. Having a totem pole output configuration allows the output stage to
both sink and source current.
The optocoupler inputs - the anodes (labeled as A) and cathodes (labeled as
C) of the internal optocoupler LEDs, are routed to the screw terminals,
which allow connection the external electrical circuit, used to trigger an
event on the isolated MCU. The electrical potential between the anode and
the cathode input of each optocoupler element should stay within the range
between 3.3V and 5V.
The optocoupler outputs are routed to the mikroBUS™. Pins INT, CS, RST,
and AN of the mikroBUS™ are routed to the optocoupler outputs 1, 2, 3, and
4, respectively, and are labeled as IN1, IN2, IN3, and IN4. As already
mentioned, the output stages are conditioned with the Schmitt trigger
circuit, reducing the input noise sensitivity and false triggering. The Faraday
shield protects the output stages against EMI and provides common-mode
transient immunity of ±20 kV/μs. Although these mikroBUS™ pins are
labeled as IN1 to IN4, they are actually outputs from the optocouplers, and it
is highly recommended to use them as the INPUT pins on the host MCU.
The Click board™ is equipped with an SMD jumper labeled as LOGIC, which
allows selection of the voltage, applied to the optocoupler output stage. This
voltage effectively determines the logic voltage level for the MCU pins. It can
be selected between 3.3V and 5V, allowing this Click board™ to be interfaced
with both 3.3V and 5V MCUs.
The provided library offers functions that simplify and speed up the
application development. The included example application demonstrates
their use. This application can be used as a reference for custom projects.
Specifications
Type Optocoupler
Used for isolation MCU input pins from the