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“This article introduces the hardware design and communication protocol of the receiving and transmitting unit of the multi-bionic robotic fish communication subsystem. Discussed the software running program of the robotic fish communication subsystem and the design method of error correction coding in communication. This method can greatly improve the reliability of MRFS, thereby providing a reliable platform for expanding MRFS functions.
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Authors: Liu Guichun, Li Xiaojian
The Multiple Robotic Fish System (MRFS) based on global vision is generally composed of four parts: robotic fish subsystem, vision subsystem, decision-making and simulation subsystem, and wireless communication subsystem. Among them, the wireless communication subsystem is mainly responsible for information interaction between decision-making and simulation subsystems and robotic fish subsystems. At this stage, the robotic fish subsystem and the decision-making and simulation subsystem mostly adopt one-way communication, that is, the control commands formed by the decision-making and simulation subsystem are sent to the robotic fish subsystem through the computer serial port and wireless transmitting unit, and the robotic fish subsystem is through The built-in wireless receiving unit receives the commands from the host computer, and the robotic fish-mounted AVR single-chip microcomputer processes the received commands, thereby controlling the behavior of the multi-bionic robotic fish to complete a certain task. Therefore, the communication system should be able to use one transmitter to send corresponding commands to multiple robotic fish. This article analyzes and describes the hardware design and communication protocol of the communication subsystem according to the real-time and accurate actual requirements of MRFS.
1 Hardware design of multi-bionic robotic fish communication subsystem
The MRFS communication system is composed of a wireless transmitting unit, a communication cable and an average line receiving unit. The wireless transmitting unit is connected to the host by a cable, so that the commands of the decision-making subsystem can be sent to the receiving unit of each robotic fish by wireless broadcast; and the wireless receiving unit is connected to the robotic fish-mounted single-chip microcomputer, which is mainly based on the command. Control the behavior of robotic fish. The structural block diagram of this communication subsystem is shown as in Fig. 1.
1.1 The hardware design of the wireless transmitting unit
In the design method introduced in this article, the core component of the wireless transmitting unit adopts a new type of ultra-small, ultra-low power consumption, high-speed wireless data transmission MODEM wireless transceiver module PTR2030. Figure 2 shows the schematic diagram of the module’s pin arrangement. . Its pin functions are as follows:
VCC: positive power supply;
CS: Channel selection terminal, this terminal must be high (ie CS=1) to select the working channel as 315 MHz;
DO: Data output terminal;
DI: Data input terminal;
GND: power ground;
PWR: Energy-saving control terminal, when PWR is high, it is in normal working state; when PWR is low, it is in standby micro power consumption state;
TXEN: Transmit and receive control terminal. When TXEN is 1, the module is in the transmitting state; when TXEN is 0, the module is in the receiving state.
The module is composed of a single IC, combining receiving and transmitting, built-in loop antenna, small size, very suitable for embedded devices; it adopts FSK modulation method, the working frequency is the international 315MHz digital transmission frequency band, and has strong anti-interference ability; The one-way transmission rate can reach 20 KB/s, and the working voltage is low (2.7～3.3 V), the power consumption is small, the current in the standby state is only 8 μA; in addition, the module is also compatible with CMOS and TTL logic, and can be directly connected with The one-chip computer serial port is connected, the programming is very convenient.
Because the control command generated by the decision-making subsystem is issued by the host through the commonly used RS-232 serial interface, and what PTR2030 can receive is TTL/CMOS level, the interface circuit needs to be level-converted. This design uses the level conversion chip ICL232 produced by Intersil to complete the conversion. The ICL232 chip contains two drivers and receivers, which can fully meet the requirements of the system. The PWR terminal of PTR2030 can be connected to high level to make it in working state; TXEN terminal can be programmed and controlled by the host computer through ICL232; DI and DO terminals are connected to the RXD and TXD of the host computer through ICL232. After ICL232 converts the RS-232 level to TTL level, it can be transmitted in the form of radio waves through the satire transmitting module PTR2030. The principle diagram of the wireless transmitting unit is shown in Figure 3.
1.2 The hardware design of the wireless receiving unit
After the control command of the decision-making subsystem is sent by the wireless transmitting unit in the way of radio waves, it is demodulated by the wireless receiving unit into a signal that can be recognized by the single-chip microcomputer and sent to the robotic fish-carrying single-chip microcomputer for processing, so as to realize the control of each robotic fish. Because the SCM system can directly receive the TTL/CMOS level, there is no need for level conversion between the PTR2030 and the SCM, and can be directly connected. In this way, the DI end of the PTR2030 wireless MODEM should be connected to the sending end of the single-chip serial port, and the DO end should be connected to the receiving end of the single-chip serial port. The I/O port of the single-chip microcomputer can be used to control the module’s emission, channel conversion and low power consumption mode. In the MRFS system, the robotic fish-mounted microcontroller adopts the new AVR microcontroller ATmega16L launched by ATMEL. The chip has an advanced RISC architecture, and its data throughput rate is as high as 1 MIPS/MHz, so it can better deal with the contradiction between power consumption and processing speed of the system, and it is very suitable for real-time and reliability requirements such as robotic fish or robots. Higher intelligence system. The principle diagram of the wireless receiving unit is shown in Figure 4.
2 Design of communication protocol
In MRFS, a PC (upper computer) usually needs to correspond to multiple robotic fish (lower computers). Therefore, the system is a master-slave data transmission system. The design adopts simplex communication mode (that is, the commands of the decision-making system are sent from the PC to each robotic fish-mounted single-chip computer). The motion information of the robotic fish is usually provided by the vision subsystem to the PC, and the robotic fish itself does not send to the PC. Order. The coordination of the simplex communication system is completely controlled by the sender. The sender uses a data frame with an address code to send data or commands, which are then all received by each robotic fish, and the received address code is compared with its own address code. If they are different, the data will be ignored (no response will be made); if the address code is the same, it proves that a robot fish has been addressed by the PC, and the robot fish will respond differently according to the sent data or commands. This transmission method can ensure that only one robotic fish is addressed at any instant, thereby avoiding mutual interference. Figure 5 shows a flowchart of a robotic fish communication subroutine. Since this system uses wireless data transmission, the data must be processed in a prescribed format. The format of the data packet is as follows:
3 Design of error correction coding
In the wireless communication system, although some anti-interference measures have been introduced in the hardware circuit, the data will inevitably be subjected to various interferences during the transmission process, so that the data received by the receiving end of the communication will be compared with the data actually sent by the sending end. The data appears inconsistent. Therefore, in order to ensure the reliability of the system, error control coding (error correction coding) measures must be added to the communication system when designing. There are mainly three commonly used error correction control methods: error detection and retransmission (ARQ), forward error correction (FEC) and hybrid error correction (HEC). This system is a simplex communication method, suitable for the use of BCH (7, 4) forward error correction packet code control with both error detection and error correction functions, so it needs to use a two-byte length to send a valid byte information. Facts have proved that this error correction method has achieved good results in both the multi-robot system and the football robot system.
4 Conclusion
This article introduces the hardware design and communication protocol of the receiving and transmitting unit of the multi-bionic robotic fish communication subsystem. Discussed the software running program of the robotic fish communication subsystem and the design method of error correction coding in communication. This method can greatly improve the reliability of MRFS, thereby providing a reliable platform for expanding MRFS functions.
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