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Raspberry Pi Overview

What Is a Raspberry Pi​

The Raspberry Pi is a small single-board computer. Besides the usual ports (USB, HDMI, network), it carries a row of GPIO pins that allow electronic components to be connected directly, which makes it a popular platform for hardware projects.

GPIO Pins​

GPIO stands for General-Purpose Input/Output. The pin header combines several kinds of pins:

  • Power pins: fixed 3.3 V and 5 V outputs to supply components.
  • Ground pins (GND): the common reference / return path for the current.
  • I/O pins: freely programmable pins that can be read (input) or set (output).

A GPIO I/O pin is purely digital: it only knows HIGH (3.3 V) and LOW (0 V). It cannot directly measure an analog voltage, so an analog sensor needs an analog-to-digital converter (ADC) in between. Conversely, an analog-like output is approximated with pulse-width modulation (PWM).

Sensors vs. Actuators​

Components fall into two opposite roles:

  • A sensor is a component that converts a physical quantity from the environment (temperature, humidity, pressure, acceleration, etc.) into an electrical signal.
  • An actuator is the counterpart of a sensor and does exactly the opposite: it converts an electrical signal into a physical quantity such as motion, pressure, sound, or light.
RoleDirectionExamples
Sensorenvironment => electrical signaltemperature sensor, light sensor
Actuatorelectrical signal => environmentmotor, lamp/LED, loudspeaker, buzzer

The Breadboard​

A breadboard allows components to be connected without soldering, wires and component legs are simply pushed into its holes. Holes that belong to the same internal strip are electrically connected:

  • The two long power rails along the edges (marked + and -) run the length of the board. They are usually fed once from a 3.3 V / 5 V pin and a GND pin, so power and ground are available everywhere.
  • The inner terminal strips connect the holes of each short column together, divided by a gap in the middle of the board.

Components plugged into the same connected strip share an electrical connection, which is how a circuit is built up.

Connecting Components​

Most components expose a few clearly defined connections. The three most common are power (VCC / +), ground (GND / -), and a signal line.

ComponentRoleConnectionsFurther Explanation
LED / lampactuatoranode (+), cathode (-)longer leg is +, shorter leg is -
Temperature sensorsensorVCC (+), GND (-), signalsignal carries the measured value to a GPIO pin
Buzzeractuator+ (signal), - (GND)the signal switches or drives the sound

Common Pin Labels​

Sensor modules and breakout boards rarely spell their connections out, instead they print short, standardized abbreviations next to each pin:

  • VDD / VDC / VCC (+): the positive supply voltage (power in). VDD and VCC stem from chip design, VDC simply means "volts DC"; in practice all three mark the power pin (e.g. 3.3 V or 5 V).
  • GND / VSS (-): ground, the common reference and return path for the current.
  • SDA: the data line of the I2C bus, over which a sensor exchanges values with the Pi.
  • SCL: the clock line of the I2C bus, which keeps both sides in step.

I2C is a two-wire bus (SDA + SCL) that lets several digital sensors share the same two GPIO pins, each one addressed individually. An I2C sensor needs no ADC, the conversion to digital values already happens inside the module.

LED / Lamp​

An LED has two legs with a fixed polarity:

  • Anode (+): the longer leg, connected toward the GPIO / positive side.
  • Cathode (-): the shorter leg (also marked by the flat edge of the rim), connected to GND.

An LED must always be driven through a series resistor to limit the current — without it, the LED draws too much current and burns out.

Temperature Sensor​

A typical sensor module has three pins:

  • VCC (+): power, e.g. 3.3 V.
  • GND (-): ground.
  • Signal: the output that carries the measurement.

If the signal is analog (a voltage proportional to the temperature), it cannot go straight into a GPIO pin, an ADC is required first.

Buzzer​

A buzzer has just two connections, + (signal) and - (GND), and comes in two variants:

  • Active buzzer: contains its own oscillator and only needs a HIGH / LOW signal to switch the sound on and off. It plays a single, fixed tone.
  • Passive buzzer: has no oscillator and can play different tones, but needs a varying signal. The pitch is set by the frequency of a PWM signal.

See Also​