What are the three servo lines? This paper analyzes the corresponding relationship between servo cables

Recently, some students often ask me questions about servo lines, including what are the three lines of the servo, what is the color of each line, how should the servo connection be connected, and what are the lines of the four-wire servo. In order to better answer your doubts, I specially wrote this article, hoping to be helpful to you.

According to the signal type, the servo CAN be divided into PWM signal servo, RS-485 serial port servo, TTL serial port servo and CAN bus servo. Although the wiring methods of various communication methods are slightly different, they all contain two positive and negative power lines. Generally use color to distinguish the function, the red line in the middle is the positive power supply, the brown line is the negative power supply, and the remaining orange line is the signal line. However, there are also cases where the positive electrode of the servo is red, the negative electrode is black, and the signal line is white. In addition to the conventional color matching of the three-wire servo line, there are also lines that are all black, and signal lines with white edges.

PWM servo connection:

In the transmission process of PWM signal, only one wire is needed to complete the transmission and reception of the signal. This is because the PWM signal is a digital signal that contains only two states, high and low, and changes in these two states can be transmitted through a single wire.

It should be noted that although the PWM signal has only one wire, its frequency and duty cycle can be adjusted by the microprocessor or other control chip. Different PWM signals can realize the digital encoding of different analog signals, so as to achieve different control functions.

In addition to the conventional three-wire servo, there is a five-wire servo, the five-wire servo has no servo control board, the Angle sensor and the motor are directly connected to the electric regulator, so the line will have two more positive and negative lines of the potentiometer.

RS-485servo：

RS-485 signals use two wires because it is A differential signal transmission method that requires two wires to transmit the difference between the signals, usually represented by A and B or D+ and D-. When sending data, the transmitter sends the data to two wires, and the receiver receives the data from both wires and compares it. Since the signals from the two wires are opposite, the receiver can extract useful signals from them.

Because RS-485 signal has the advantages of strong anti-interference ability, long transmission distance and signal stability, RS-485 servo has been widely used in industrial automation, robot arm, remote control and other fields.

TTLservo：

TTL servo is the same as PWM servo, there is only one signal line, the difference is that TTL signal is transmitted through the voltage level. In TTL circuit, when the input is high level, the output is also high level. When the input level is low, the output level is low.

TTL interface usually has VCC, GND, TXD and RXD four lines, but you can use the serial to single line communication circuit to mount the original two-wire duplex serial device to the single-bus circuit of single-wire half-duplex. The process of sending and receiving data needs to be controlled by the master device, which determines whether the bus is used to send or receive data at a certain time.

TTL double wire to single wire

In addition, the anti-interference ability of TTL signal is weak, and it is easy to be affected by electromagnetic interference. Therefore, its transmission distance is generally short.

CAN bus servo:

CAN bus and RS485 are similar, are two-wire differential signals, divided into CAN_H and CAN_L two buses. When the CAN node sends data, it sends data simultaneously through two wires CAN_H and CAN_L, and the receiving node judges the logical state of the data by comparing the voltage difference between the two wires. Since the signals of the two wires are opposite, the receiving node can extract useful signals from them.

The difference between CAN bus and RS485 is that RS485 is a single master-slave structure, that is, there can only be one host on a bus. The CAN bus is a multi-master-slave structure, each node has a CAN controller, when multiple nodes are sent, the ID number is automatically arbitrated, so that the bus data can be realized is not bad, and after a node is sent, another node can detect the bus idle, and immediately sent, which saves the host's inquiry, improves the bus utilization rate, and enhances the rapidity. Therefore, CAN bus servo is often used in automobiles, smart homes and other systems with high real requirements.

Original link:https://blog.csdn.net/lanxiaoke123/article/details/92840243

In general, each communication protocol servo wiring are different, signal line color is not strict standards, therefore, want to understand their own servo wiring, you can refer to the relevant information, compare different communication protocols wiring methods, combined with their actual needs for analysis and judgment, you can also consult professionals. Non-professionals had better not dismantle the machine, easy to cause damage to the servo.