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We Interrupt This Program...

Raspberry Pi Interrupts With the GPIO

Issue: 24.3 (May/June 2026)
Author: Eugene Dakin
Author Bio: Eugene works as a Senior Oilfield Technical Specialist. He has university degrees in the disciplines of Engineering, Chemistry, Biology, Business, and a Ph.D. in Chemical Engineering. He is the author of dozens of books on Xojo available on the xdevlibrary.com website.
Article Description: Interrupts on Raspberry Pi GPIO electronics efficiently handle external voltage changes, such as button presses or sensor feedback, by triggering an interrupt service routine (ISR) instead of wasting CPU cycles through polling. This immediacy and reliability are crucial for real-time applications like robot control or sensor monitoring, as interrupts can promptly respond to fast-changing signals without missing events. The text details using a low-level library, lgpio, with Xojo to manage GPIO events, providing examples for raw interrupts and enhanced stability with debounce to prevent multiple triggers from a single button press due to electrical noise. The setup involves configuring a Raspberry Pi (preferably Pi 4 or 5) with the necessary libraries and wiring a switch to GPIO Pin 17, while the code illustrates initializing GPIO, setting up interrupt callbacks, and implementing debounce logic by checking the time elapsed since the last interrupt. Overall, interrupts offer a significant advantage in reducing CPU usage and ensuring accurate data acquisition from physical interactions..
Article Length (in bytes): 12,629
Starting Page Number: 15
Article Number: 24303
Resource File(s):

project24303.zip Updated: 2026-05-04 10:01:23

Related Link(s): None

Excerpt of article text...

Interrupts with GPIO electronics on the Raspberry Pi respond to external changes in voltage, usually from +3.3 volts to 0.0 volts. These changes can be triggered by a button being pressed or by sensor feedback. Since loops can waste CPU cycles by polling a pin, interrupts are more efficient, allowing the CPU to perform other tasks, such as graphics. When the interrupt event occurs, an interrupt service routine (ISR) is triggered, and a method is called to handle the actions of the triggered event.

Interrupts are efficient, allowing the program to wait passively, and the method fires only when the event occurs. Interrupts are immediate, meaning they can react to a real-time event instantly, which is better for controlling a robot or monitoring a sensor. Another benefit of interrupts is their reliability for fast-changing signals, as regular polling can be unreliable and may miss events.

In summary, the interrupt acts like a doorbell that activates when an event occurs in the real world.

This example uses a low-level library called lgpio to handle the GPIO events directly. This allows the program to respond immediately to external signals without constant CPU polling. There are two examples: the first explains and provides code to have the raw interrupt working, while the second example adds debounce for increased interrupt stability.

Figure 1 is a screen grab of a Xojo program using version 1.33 of the free lgpio module available at my GitHub site (https://github.com/eugenedakin/lgpio-GPIO). When wired up and connected to Pin 17 with a resistor and switch, the program automatically starts running when launched. Press the physical button to cause a 3.3-volt spike to the pin, and the count number will increase. The Xojo program calculates the number of times the voltage of Pin 17 has reached 3.3 volts.

In this case, the physical button has been pressed six times, which has increased the voltage from 0.0 volts to 3.3 volts on six occasions.

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