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GPIO and PWM: switching and controlling pins

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tagsglossar, elektronik, raspberry-pi

2 min read

GPIO and PWM: switching and controlling pins

In short: GPIO pins are freely programmable digital inputs and outputs of microcontrollers; with PWM brightness, motors and servos can be controlled without exceeding the pins’ current capacity.

In more detail: GPIO (general purpose input/output) are pins that a program uses as input (read a button) or output (switch an LED). On Raspberry Pi, Pico, Arduino and ESP32 this connects software with the world.

In Depth

Inputs and outputs

  • Output: HIGH (3.3 V/5 V) or LOW (0 V); current per pin limited (Arduino ≈ 20 mA, Pi ≈ 16 mA, mind the total); LED with series resistor, larger loads via transistor/MOSFET/relay driver.
  • Input: reading a button; an open input floats (reads randomness) → pull-up or pull-down (internally activatable: INPUT_PULLUP).
  • Debouncing: mechanical buttons bounce for a few ms → software debouncing/capacitor.
  • Interrupts: an edge triggers a function (instead of constant polling).

PWM (pulse-width modulation)

Fast on/off with adjustable duty cycle. The average acts like an analogue voltage: 25 % on → about ¼ brightness/power.

# MicroPython (Raspberry Pi Pico)
from machine import Pin, PWM
led = PWM(Pin(15)); led.freq(1000)
led.duty_u16(32768)      # 50 %

Uses: dimming LEDs, motor speed, servo (pulses of 1–2 ms every 20 ms for angle), tones (speaker), fan control. Frequency high enough (avoid flicker/whine).

Analogue and levels

  • ADC reads voltages (0–3.3 V → 0–1023/4095), e.g. potentiometer, light sensor; Raspberry Pi has no ADC (external needed, MCP3008). Outputting DAC is rare; PWM + filter often suffices.
  • 3.3 V vs. 5 V: only tolerant pins/level shifters; 5 V on a 3.3 V GPIO can destroy it.
  • Connect GND in common.
  • Motors/servos with own power supply and common ground, flyback diode; not directly on the pin.
  • Protection: series resistors, ESD caution.

Programming

  • Arduino: pinMode, digitalWrite, digitalRead, analogWrite.
  • Raspberry Pi: gpiozero (LED(17).on(), Button(2)), libgpiod; (RPi.GPIO old). Distinguish pin numbering (BCM vs. board).
  • MicroPython/CircuitPython on Pico/ESP32.
  • Linux level: gpiod tools, device tree.
  • Projects: button-LED, traffic light, temperature sensor + display (I²C), servo control, retro case with power button, fan curve.
  • Safety: never mains voltage directly; relay modules with isolation only with expertise.

See also: I²C, SPI and UART, Raspberry Pi, Arduino and microcontrollers, Electronic components

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