Pin interrupt library for AVR microcontrollers

This library can help to easily configure a pin interrupt on AVR microcontrollers without the need to check the datasheet every time. At the moment only PCINT pins are supported.

In this blog post, I will explain how to use interrupts on AVR microcontrollers. Interrupts are a powerful feature that allow the microcontroller to respond to external or internal events without constantly polling for them. Interrupts can improve the performance and efficiency of your code, as well as enable new functionalities.

What are interrupts?

An interrupt is a signal that causes the microcontroller to temporarily stop its current execution and jump to a special function called an interrupt service routine (ISR). The ISR performs the necessary actions to handle the interrupt, and then returns to the original program flow. The ISR can be triggered by various sources, such as:

• External pins (EXTINT)
• Pin changes (PCINT)
• Timers/Counters (TIMER)
• Serial communication (USART, SPI, TWI)
• Analog-to-digital conversion (ADC)
• Analog comparator (AC)
• Watchdog timer (WDT)
• EEPROM ready (EE READY)
• Store program memory ready (SPM READY)

stepperCon library for controlling stepper motor drivers using timer interrupt on AVR devices

The stepperCon library allows you to control multiple stepper motors at the same time. It can interface with any stepper motor driver that can take inputs such as step and direction. The library also has some extra useful functionalities such as motor coordination using Bresenham line algorithm - useful for controlling 3 axis motors for example, free spin - where the motor keeps spinning, and positioning the motor at a certain degree from 1 to 360 by finding the shortest path.

The maximum speed (step rate) on a 16MHz microcontroller is 25kHz, however the maximum practical speed is 6.25kHz or 8.33kHz depending on the motor, load, supply voltage and micro-step resolution. A higher voltage can yield higher RPM and with 1/32 micro-step resolution the step rate can be 25kHz as oppose to 6.25kHz when using 1/8 micro-step resolution.

Even with multiple motors running at the same time, the speed can be maintained and that is because the speed profile is segmented and calculated while the interrupt routine (ISR) is not executing steps. So the time spent inside the ISR is low since the calculations for acceleration and deceleration are not done there. Only the stepping is done inside the ISR. Having an interrupt to generate the steps is preferred over a function in the main loop where other code could delay the stepping function thus causing motor stuttering.

The stepper library includes the micros library that is used to trigger a timer interrupt every 40us and as a perk you also have a way to keep track of time in your project with a 40us time resolution.

 

stepperCon library characteristics

• interface with multiple stepper motor drivers
• up to 3 coordinated motors for X, Y and Z (can be extended for more)
• maximum stepping rate speed of 6.25kHz (or 8.33kHz if the motor can have high acceleration). Speeds are given for a 16MHz CPU. With higher CPU clock the stepping rate will also be higher.
• angular positioning function that finds the shortest path from current angle to target angle
• perpetual motion
• timer interrupt driven
• individual settings for acceleration and deceleration