Many Arduino enthusiasts utilize servo motors in their projects, relying on the convenience of the built-in Servo library. However, questions often arise about the inner workings of this library, especially when users encounter timer conflicts or explore alternative libraries like ServoTimer2. This article delves into the mechanics of the Arduino Servo library, addressing common curiosities about its operation and pulse generation.
One might initially assume that the Servo library generates pulses for all connected servo motors simultaneously. Imagine controlling multiple servos; a naive approach could involve setting all pulse signals high at once, then sequentially turning them off based on each servo’s desired position. This method would require recalculating the pulse order whenever a servo position changes.
However, the standard Arduino Servo library, and libraries like ServoTimer2, operate differently. Instead of simultaneous pulses, they generate pulses sequentially. This means a pulse is sent to one servo, and after it concludes, the pulse for the next servo begins. This sequential approach might seem less efficient at first glance, especially when libraries like ServoTimer2 are mentioned as potentially using an 8-bit timer, seemingly limiting the number of controllable servos compared to the standard library’s capacity for 12 servos.
The question then becomes: how can the standard Servo library manage up to 12 servos if pulses are sequential? If each servo at 180 degrees requires a 2ms pulse, and we have 12 servos, the total pulse duration in a strictly simultaneous system could reach 24ms. This would result in a refresh rate of approximately 41.7Hz, falling below the common 50Hz refresh rate for servos.
The key to understanding this lies in the sequential nature of pulse generation. The Servo library manages to control multiple servos by sending pulses one after another within the 20ms refresh cycle (which equates to 50Hz). While the pulses are not simultaneous, the library ensures that each servo receives its control pulse within the necessary timeframe. This method cleverly utilizes timer interrupts to schedule and deliver these sequential pulses efficiently, maximizing the number of servos an Arduino can control without requiring complex, simultaneous pulse generation hardware.
Therefore, the Arduino Servo library employs a sequential pulse method. It does not send pulses to all servos at the exact same moment, but rather manages to control multiple servos effectively by delivering precisely timed pulses, one after another, within the standard servo refresh cycle. This approach allows for control of multiple servos even with timer limitations and without the need for simultaneous pulse generation.
