When it comes to controlling servo motors, various communication methods are available. While modern systems often favor USB or dedicated servo control protocols, the question of using traditional RS232 serial communication sometimes arises. This article explores the possibilities and challenges of Serial Servo Wiring using RS232, particularly in the context of servo controllers like the Maestro, and discusses why alternative methods might be more practical for most applications.
One might consider using a standard RS232 serial COM port from a computer to directly interface with a servo controller. In theory, this approach is possible, but it’s crucial to understand the electrical differences between RS232 and the TTL (Transistor-Transistor Logic) levels that most servo controllers, including the Maestro, operate on.
RS232 specifications define voltage levels ranging from ±3 to ±15 volts, although the actual voltage can vary depending on the specific computer’s port implementation. These voltage levels are incompatible with the TTL levels (0 to 5V) expected by servo controllers like the Maestro. Directly connecting an RS232 port to a Maestro or similar controller without proper voltage adjustment can lead to damage or malfunction.
To bridge this gap, voltage level shifting is essential. A level shifting circuit is required to convert the RS232 voltage levels to TTL levels for transmission to the servo controller (TxD line) and to perform the reverse conversion for signals coming back from the controller to the computer (RxD line). Implementing such a circuit adds complexity to the wiring and requires careful consideration to ensure proper signal levels and reliable communication.
For basic serial communication, only three wires are strictly necessary: Transmit Data (TxD), Receive Data (RxD), and Ground (Earth). When wiring for serial servo control with RS232, ensure the ground pin of the RS232 connector is connected to the ground on the Maestro. The TxD pin of the RS232 port should be connected to the Rx pin of the Maestro (via the voltage level shifting circuit), and conversely, the RxD pin of the RS232 port connects to the Tx pin of the Maestro (again, through level shifting).
It’s also worth considering whether two-way communication is actually needed. If control is only required in one direction – sending commands to the servos – then you might only need to utilize the TxD line (with voltage level shifting) and ground connection.
Software like LabVIEW can be used to control serial COM ports, similar to how it manages virtual COM ports. This allows for programming and sending serial commands to the servo controller.
However, despite the theoretical feasibility of RS232 serial servo wiring, the USB to virtual COM port method is generally a more straightforward and highly recommended approach for modern systems. Servo controllers like the Maestro are designed to be easily controlled via USB, which simplifies wiring, eliminates the need for external level shifting circuits, and often provides faster and more reliable communication. USB connections also typically offer plug-and-play convenience and better integration with modern operating systems and software environments.
In conclusion, while RS232 serial servo wiring is technically possible with the inclusion of voltage level shifting and careful wiring, it introduces unnecessary complexity compared to using USB. For most users, especially those seeking ease of use and reliable performance, leveraging the USB interface and virtual COM port capabilities of modern servo controllers like the Maestro is the preferred and more practical solution for serial servo wiring and control. The versatility of boards like the Maestro is better realized through their intended USB interface, offering a smoother and more efficient path to servo control.
