The pins are your board's way to communicate with external devices connected to it. There are 19 pins for your disposal, numbered 0-16 and 19-20. Pins 17 and 18 are not available.
For example, the script below will change the display on the micro:bit depending upon the digital reading on pin 0:
from microbit import *
while True:
if pin0.read_digital():
display.show(Image.HAPPY)
else:
display.show(Image.SAD)
Those pins are available as attributes on the microbit module:microbit.pin0 - microbit.pin20.
+-----+---------+----------+ | Pin | Type | Function | +=====+=========+==========+ | 0 | Touch | Pad 0 | +-----+---------+----------+ | 1 | Touch | Pad 1 | +-----+---------+----------+ | 2 | Touch | Pad 2 | +-----+---------+----------+ | 3 | Analog | Column 1 | +-----+---------+----------+ | 4 | Analog | Column 2 | +-----+---------+----------+ | 5 | Digital | Button A | +-----+---------+----------+ | 6 | Digital | Row 2 | +-----+---------+----------+ | 7 | Digital | Row 1 | +-----+---------+----------+ | 8 | Digital | | +-----+---------+----------+ | 9 | Digital | Row 3 | +-----+---------+----------+ | 10 | Analog | Column 3 | +-----+---------+----------+ | 11 | Digital | Button B | +-----+---------+----------+ | 12 | Digital | | +-----+---------+----------+ | 13 | Digital | SPI MOSI | +-----+---------+----------+ | 14 | Digital | SPI MISO | +-----+---------+----------+ | 15 | Digital | SPI SCK | +-----+---------+----------+ | 16 | Digital | | +-----+---------+----------+ +-----+---------+----------+ | 19 | Digital | I2C SCL | +-----+---------+----------+ | 20 | Digital | I2C SDA | +-----+---------+----------+
The above table summarizes the pins available, their types (see below) and what they are internally connected to.
The pins of your board cannot output analog signal the way an audio amplifier can do it -- by modulating the voltage on the pin. Those pins can only either enable the full 3.3V output, or pull it down to 0V. However, it is still possible to control the brightness of LEDs or speed of an electric motor, by switching that voltage on and off very fast, and controlling how long it is on and how long it is off. This technique is called Pulse-Width Modulation (PWM), and that's what the write_analog method below does.
Above you can see the diagrams of three different PWM signals. All of them have the same period (and thus frequency), but they have different duty cycles.
The first one would be generated by write_analog(511), as it has exactly 50% duty -- the power is on half of the time, and off half of the time. The result of that is that the total energy of this signal is the same, as if it was 1.65V instead of 3.3V.
The second signal has 25% duty cycle, and could be generated with write_analog(255). It has similar effect as if 0.825V was being output on that pin.
The third signal has 75% duty cycle, and can be generated with write_analog(767). It has three times as much energy, as the second signal, and is equivalent to outputting 2.475V on th pin.
Note that this works well with devices such as motors, which have huge inertia by themselves, or LEDs, which blink too fast for the human eye to see the difference, but will not work so good with generating sound waves. This board can only generate square wave sounds on itself, which sound pretty much like the very old computer games -- mostly because those games also only could do that.
There are three kinds of pins, differing in what is available for them. They are represented by the below classes. Note that they form a hierarchy, so that each class has all the functionality of the previous class, and adds its own to that.
Note
Those classes are not actually available for the user, you can't create new instances of them. You can only use the instances already provided, representing the physical pins on your board.