User Manual
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14 EasyVR 3 User Manual (1.0.14)
General Purpose I/O
Since the EasyVR communication interface takes two pins of the host controller, a few spare I/O pins are
provided, which can be controlled with the communication protocol, to get those pins back for basic
tasks, such as lighting an LED or reading a switch.
The six I/O pins IO1–IO6 are connected directly to the embedded microcontroller on the EasyVR module,
so they are referenced to the internal 3.0V regulated power supply VDD. If you need to interface to
circuits using a different supply, there are a number of solutions you can adopt. Some of these are
outlined below (here IOn indicates any one of the six I/O pins of the EasyVR).
Use a pin as an output
All the I/O pins are inputs with weak internal pull-up after power on. You must explicitly configure a pin
before you can use it as an output (see the example code Use general purpose I/O pins).
IOn
LED
IOn
Inverted
OUT
5V
IOn
-
12V
RELAY
Z
Switched
Load
AC MAINS
Voltage
I/O pin directly driving a
low-current LED
I/O pin connected to high
impedance 5V circuit (such as
MCU input pin)
I/O pin switching a load on a high voltage
line using a 12V relay
The exact components values in these circuits may vary. You need to calculate required values for your
application and choice of components. For example, resistor value for the LED circuit can be calculated
approximately as:
Where V
LED
is the LED forward voltage, as reported on the LED datasheet, at the driving current I
OH
(see
section Electrical Characteristics). Let’s assume a typical low-current LED has a V
F
=1.8V at 5mA, the
resistor value is:
Now stay on the safe side and choose a slightly larger resistor, such as 150Ω.
If you want to drive higher current LEDs, you need a circuit like the second one, where you put the LED
between the output resistor and the collector of the NPN transistor.
Use a pin as an input
All the I/O pins are inputs with weak internal pull-up after power on or reset. You may also configure the
pin to have a strong pull-up or no pull-up at all (see the example code Use general purpose I/O pins).