docs: add English version of GPIO article

docs/en/SUMMARY.md

@@ -45,6 +45,7 @@
   * [Computer vision basics](camera.md)
   * [LED strip](leds.md)
   * [Using rviz and rqt](rviz.md)
+  * [Working with GPIO](gpio.md)
   * [Interfacing with a sonar](sonar.md)
   * [Interfacing with a laser rangefinder](laser.md)
   * [PX4 Simulation](sitl.md)

docs/en/gpio.md

@@ -0,0 +1,96 @@
+# Working with GPIO
+
+GPIO (General-Purpose Input/Output) – is a type of Raspberry Pi's pins, with programmatically adjustable and measurable voltage. On some of the pins there also is hardware implemented <abbr title="Pulse-width modulation">PWM</abbr>.
+
+> **Info** Use the [pinout](https://pinout.xyz) for figuring out, which Raspberry Pi's pins support GPIO and PWM.
+
+[The RPi image](microsd_images.md) includes [`pigpio`](http://abyz.me.uk/rpi/pigpio/) library for work with GPIO. To interact with this library, run the appropriate daemon:
+
+```bash
+sudo systemctl start pigpiod.service
+```
+
+For enabling automatic launch of the daemon, use command:
+
+```bash
+sudo systemctl enable pigpiod.service
+```
+
+Example of working with the library:
+
+```python
+import time
+import pigpio
+
+# initializing connection to pigpiod
+pi = pigpio.pi()
+
+# setting pin 11 mode for output
+pi.set_mode(11, pigpio.OUTPUT)
+
+# enabling signal of pin 11
+pi.write(11, 1)
+
+time.sleep(2)
+
+# disabling signal on pin 11
+pi.write(11, 0)
+
+# ...
+
+# setting pin 12 mode for input
+pi.set_mode(12, pigpio.INPUT)
+
+# read the state of pin 12
+level = pi.read(12)
+```
+
+For finding out pins' numbers, use the [Raspberry Pi pinout](https://pinout.xyz).
+
+## Connecting servos
+
+Most of servos are controlled with PWM signal. Extreme positions of servos are reached with signal widths approximately equal to 1000 and 2000 µs. Values for a specific servo can be determined experimentally.
+
+Connect the signal wire of the servo to one of GPIO-pins of the Raspberry. For controlling a servo, connected to the pin 13, use a code like this:
+
+```python
+import time
+import pigpio
+
+pi = pigpio.pi()
+
+# setting mode of pin 13 to output
+pi.set_mode(13, pigpio.OUTPUT)
+
+# setting pin 13 to output PWM signal 1000 us
+pi.set_servo_pulsewidth(13, 1000)
+
+time.sleep(2)
+
+# setting pin 13 to output PWM signal 2000 us
+pi.set_servo_pulsewidth(13, 2000)
+```
+
+## Connecting electromagnet
+
+![GPIO Mosfet Magnet Connection](../assets/gpio_mosfet_magnet.png)
+
+For connecting an electromagnet, use a field-effect transistor (MOSFET). Connect the MOSFET to one of GPIO-pins of the Raspberry Pi. For controlling the magnet, connected to the pin 15, use a code like this:
+
+```python
+import time
+import pigpio
+
+pi = pigpio.pi()
+
+# setting mode of pin 15 for output
+pi.set_mode(15, pigpio.OUTPUT)
+
+# enabling the magnet
+pi.write(15, 1)
+
+time.sleep(2)
+
+# disabling the magnet
+pi.write(15, 0)
+```