Digital input (GPIO.input) in Raspberry Pi - Step-by-Step Execution

Concept Flow - Digital input (GPIO.input)

Setup GPIO pin as input

↓

Read pin state with GPIO.input

↓

Check if pin is HIGH or LOW

↓

Use pin state in program

↓

Repeat or Exit

This flow shows how to set a pin as input, read its digital state, and use that value in your program.

Execution Sample

Raspberry Pi

import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.IN)
state = GPIO.input(17)
print(state)

This code sets GPIO pin 17 as input, reads its digital state (0 or 1), and prints it.

Execution Table

Step	Action	Pin 17 Mode	GPIO.input(17) Result	Output
1	Set GPIO mode to BCM	Not set yet	N/A	No output
2	Setup pin 17 as input	Input	N/A	No output
3	Read pin 17 state	Input	0 (LOW) or 1 (HIGH)	No output yet
4	Print state	Input	0 or 1	Prints 0 or 1 to console

💡 Program ends after printing the pin state.

Variable Tracker

Variable	Start	After GPIO.setup	After GPIO.input	Final
state	Undefined	Undefined	0 or 1	0 or 1

Key Moments - 3 Insights

Why do we need to set the pin mode before reading it?

GPIO pins must be set as input or output first; otherwise, GPIO.input won't know how to read the pin. See execution_table step 2 where pin mode changes to input.

What does GPIO.input(17) return?

It returns 0 if the pin voltage is LOW (off) or 1 if HIGH (on). This is shown in execution_table step 3.

Can GPIO.input return values other than 0 or 1?

No, GPIO.input only returns digital states: 0 (LOW) or 1 (HIGH), never other numbers.

Visual Quiz - 3 Questions

Look at the execution_table, what is the pin mode after step 2?

A Output

B Not set

C Input

D Analog

💡 Hint

Check the 'Pin 17 Mode' column in execution_table row for step 2.

At which step does GPIO.input(17) return the pin state?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'GPIO.input(17) Result' column in execution_table.

If the pin is connected to 3.3V, what will GPIO.input(17) return?

A 1

B 0

C -1

D It depends on the pin mode

💡 Hint

GPIO.input returns 1 for HIGH voltage, see key_moments about return values.

Concept Snapshot

GPIO.input reads the digital state of a pin.
1. Set pin mode to input with GPIO.setup(pin, GPIO.IN).
2. Call GPIO.input(pin) to get 0 (LOW) or 1 (HIGH).
3. Use the returned value in your program.
Always set mode before reading.
Returns only 0 or 1.

Full Transcript

This lesson shows how to read a digital input from a Raspberry Pi GPIO pin. First, you set the pin mode to input using GPIO.setup. Then, you read the pin state with GPIO.input, which returns 0 if the pin is LOW or 1 if it is HIGH. Finally, you can use this value in your program, for example, printing it. The execution table traces these steps, showing the pin mode changes and the input reading. Key points include the need to set the pin mode before reading and that GPIO.input only returns 0 or 1. The visual quiz tests understanding of these steps and values.