Development of a multi-channel remote control stim

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Development of a constant current multi-channel remote control stimulation system for animal robots

0 introduction

animal robots are robots that use animals in nature as the body of motion. They achieve the purpose of controlling animal motion by implanting microelectrodes into brain nuclei or direction sensing areas related to animal motion and applying artificial simulated neuroelectrical signals. Compared with bionic robots, animal robots have attracted the attention of the world's powerful countries because of their better environmental adaptability, concealment, flexibility and reliability of movement. In recent years, the research on animal robots at home and abroad has developed vigorously. Scientists have carried out the research on robot cockroaches, robot mice, robot turtles, robot pigeons, and robot geckos, and have made many exciting achievements. In 2001, Professor Isao Shimoyama of the University of Tokyo, Japan, equipped cockroaches with electronic backpacks. Through appropriate stimulation, cockroaches can turn left and right according to instructions; In 2002, Nature magazine reported that Professor Chapin of the State University of New York Medical Center in the United States implanted electrodes into different brain regions of rats and controlled rats to walk along a pre-designed route under the stimulation of artificial electrical signals; In 2007, the robot research center of Shandong University of science and technology initially realized the control of pigeons to fly according to human instructions, becoming the world's first robot bird III; The Institute of bionic structure and material protection of Nanjing University of Aeronautics and Astronautics selected gecko with special movement ability as the research object, took the lead in conducting artificial induction research on gecko movement at home and abroad, measured the spatial distribution of gecko brain area and movement related nuclei, revealed the space-time coding law of gecko neuroelectric signals, and successfully realized the left turn, right turn Artificial induction of basic motor behaviors such as moving forward and avoiding

among the many factors that determine the success of the development of animal robots, the remote control stimulation system of animal robots is one of the key factors. It is the only way for animal robots to get rid of all kinds of constraints and realize free movement. It is also the necessary condition for animal robots to get rid of signal lines and get out of the laboratory. It requires reliable operation, low energy consumption, high efficiency and long transmission. In order to accurately control animals with individual differences, the remote control stimulation system and then change the handwheel also requires independent adjustment of various electrical stimulation parameters. In addition, due to the limitations of animal posture and animal weight-bearing capacity, the backpack remote control micro stimulator that controls animal movement behavior generally has strict requirements for size and weight

l development of wireless signal transmitting station

the animal robot remote control stimulation system developed here is composed of two parts: remote control signal transmitting station and knapsack micro stimulator (as shown in Figure 1)

the wireless signal transmitting station is composed of a PC installed with labview8.20 program operation interface and a wireless signal transmitting station connected through RS 232 serial port line. The atmega8l microprocessor located on the wireless signal transmitting station first receives the stimulation parameter signal from the PC serial port, and after receiving the data, it will judge whether the data is right or wrong according to the data format specified by the author. If the data is correct, the atmega8l microprocessor located on the wireless signal transmitting station will send this command string to the wireless signal transmitter, and these data will be sent out at the moment of sending, If the data is wrong, the microprocessor will discard it automatically. At each step of this process, two light-emitting diodes located on the wireless signal transmitting station will prompt the operator in different lighting ways

1.1 LabVIEW control program based on PC

in this system, PC and microprocessor atmega8l of wireless signal transmitter communicate through RS 232 serial port. There are two ways to use serial communication in Lab View: using visa and using axtivex (using MSComm). Programming with axtivex is relatively complex, and communicating with visa in LabVIEW is convenient and not prone to errors. Therefore, the former is adopted in the design, which uses visa function module to read and write data to serial devices in the virtual environment. The serial communication VI of labview8.20 is located in the serial of in strlament I/O Platte, which includes 8 VI nodes. When using visa for serial communication, it is necessary to install a mechanism to prevent and resolve excess capacity, which should be driven by the version, otherwise communication cannot be carried out

(1) call visaconfigure serial port to complete the setting of serial port parameters, including serial port resource allocation, baud rate, check bit, etc. the baud rate must be set correctly during serial communication, otherwise the communication data is wrong, and the baud rate is set to 9600 B./s in this system

(2) send data with visa write and receive data with visa read. Before receiving data, you need to use visabbytes at serial port to query the number of data bytes in the current serial port receiving buffer

(3) after the serial port is used, use visa close to end the session with the serial port specified by visa resource name and close the occupied serial port resources

stimulation parameters are set in double precision (DBL) data format on the LabVlEW operation interface of PC. after clicking the stimulation button, the data in double precision format will create an array containing all stimulation parameters in order. Since LabVIEW serial port can only read and write character strings, it is necessary to transform the array in double precision data format to transmit through serial port, Here, the conversion command from array to string is used to convert the double precision data array into the corresponding string. In order to prevent errors in data transmission from the computer to the wireless signal transmitting station, the data packet format of serial communication is specified: the length of the stimulus parameter data string is 24, and the first two and the 24th characters of the data are y. The correctness and error of the data are judged by the microprocessor of the wireless signal transmitting station. After the data is judged to be correct, it is transmitted, and the data error is automatically discarded. From the perspective of use safety, the emergency stop function is necessary for the knapsack micro stimulator. In order to realize this function, define the 23rd command because the breathing bag must be folded when not in use. If the 23rd byte is y, the knapsack micro stimulator is considered as a stimulation command; If it is O, it is an emergency stop command, and the microprocessor of the knapsack micro stimulator immediately enters the emergency stop state. In the command bytes, some data is reserved for the expansion of system functions in the future. They have no practical significance and are transmitted with the character 0. The communication program between PC and microcontroller based on labview8.20 is shown in Figure 2

1.2 wireless signal transmitter

the function of wireless signal transmitter is to send the stimulation parameters set by PC machine to knapsack micro stimulator in the form of wireless signal. It consists of the following parts: wireless signal transmitter, step-down and voltage stabilizing circuit composed of amslll7 3.3, atmega8l microprocessor, and level conversion circuit between PC serial port and single chip microcomputer serial port. The connection relationship between the circuits of each part of the wireless signal transmitting station is shown in Figure 3. Based on cclloo wireless transceiver ccllooa 01 (Ritchie International Trade Co., Ltd.) is a low-cost, low-power ultra-high frequency (UHF) transceiver. The module is small in size (20 mm, 30 mm, 6 mm), light in weight (2.3 g), and has a transmission distance of more than 200 m. It mainly works in ism and SRD frequency bands

because the logic o of RS 232 serial port is specified between 5 ~ 15 V, and the logic 1 is specified between - 5 ~ 15 v. The single chip microcomputer can only receive TTL level (input high level 2.4 V, input low level 0.8 V, noise tolerance is O.4 V). Therefore, the PC machine and the single chip microcomputer cannot communicate directly through the serial port line, and must undergo level conversion. Here, the.Rs 232 interface chip MAX3232 produced by Maxim company is selected, which uses a single power supply voltage for power supply, and the power supply voltage can work normally in the range of 3.0 ~ 5.5 v. The system uses a 9-pin serial port and completes communication through three lines: RXD, TXD and GND, corresponding to line 2, line 3 and line 5 on the 9-pin serial port. In the system design, the chip max323 is powered by 5.0 V voltage, and the single chip microcomputer is powered by 3.3 V voltage. Therefore, the 3.3 V voltage stabilizing chip amslll7 3.3 is selected, and the whole transmitting station can receive power from PC through USB interface

2 development of knapsack micro stimulator

for the whole system, animal knapsack micro stimulator occupies the core position, its importance is greater than other parts of the system, and its development is also more difficult. It requires not only reliable working performance, but also low energy consumption and small size. Light weight, long remote control distance. In order to meet the design requirements, the design of the micro stimulator adopts the following parts: atmega8l microprocessor, wireless signal receiver, dual phase voltage pulse generation unit composed of D/a conversion chip ad5310 and () P07 operational amplifier, bidirectional analog switch CD4051B, voltage controlled constant current circuit composed of operational amplifier lm358 and resistance, negative pressure circuit composed of TC7660 chip, voltage doubling circuit composed of TC7660 chip Led working state indication circuit and two rechargeable polymer lithium batteries (4.1 V, 180 MAH)

the wireless transceiver module ccll00a-01 can send and receive data, and its size is small and its weight is light. Therefore, it is also suitable to be used as the receiving module of remote stimulation parameter data of micro stimulator. The single 10 bit serial D/a conversion chip ad5310 is combined with () P07 to generate two-phase voltage pulse signals (as shown in Figure 4). These two-phase voltage signals are converted into corresponding two-phase constant current pulse signals through the voltage controlled current source circuit (VCCS) composed of lm358 and resistors. Under the control of the single chip microcomputer, the analog switch CD4051 sends these constant current pulses to the first to fourth stimulation channels in turn, so that the required constant current pulse signals are generated on the four channels in turn (as shown in Figure 5). The device can achieve multi-channel joint stimulation, and each channel is a biphasic pulse with adjustable current intensity. When it is necessary to select any of the four channels for multi-point joint stimulation, set the stimulation intensity of those channels that do not need to be selected to 0. In order to improve the ability of the circuit to drive the load, 4.1 V polymer lithium battery is selected, and the voltage doubling and negative pressure are carried out through TC7660, which is specially used to supply 8.2 V power to the voltage controlled constant current circuit and the analog switch CD4051; The operational amplifier (P07) used to generate two-phase voltage pulses selects 4.1 V power supply; The wireless receiver uses 5 KQ and 41 KQ resistors to divide 4.1 V into about 3.6 V power supply. In the design of knapsack micro stimulator, surface mounted electronic components with small package (0603 package) and polymer lithium battery with high power density (4.4 g, 180 MAH) are used. Therefore, the overall size of the micro stimulator is greatly reduced. The overall size is about 33 mm 24 mm 16 mm, and the mass of the battery is about 14.8 g, which is within the load range of the gecko's free movement. The ultra-low power circuit design enables the micro stimulator to be used for more than 5 hours when the battery is fully charged. After proper program delay, the knapsack micro stimulator can generate bidirectional constant current pulses with a pulse width of 1 ms, a frequency of 50 ~ 125 Hz, and an intensity of about O ~ 40 A (when the load resistance is 100 K). Because the system uses a mature commercial wireless communication module, its wireless communication performance is stable, and the remote control distance is about 200 m

in the artificial induction experiment of gecko movement, the device is sensitive to the stimulation of brain nuclei with medium and high sensitivity

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