CN102426297B - Wireless multipoint soil resistivity measuring system - Google Patents

Wireless multipoint soil resistivity measuring system Download PDF

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Publication number
CN102426297B
CN102426297B CN201110235553.1A CN201110235553A CN102426297B CN 102426297 B CN102426297 B CN 102426297B CN 201110235553 A CN201110235553 A CN 201110235553A CN 102426297 B CN102426297 B CN 102426297B
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circuit
wireless
soil resistivity
chip microcomputer
data
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CN102426297A (en
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卢超
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Shaanxi University of Technology
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Shaanxi University of Technology
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Abstract

The invention discloses a wireless multipoint soil resistivity measuring system. A soil resistivity measuring circuit is designed according to a principle of 'current-voltage four-electrode method', and a self-made mini-probe is used for reducing the interference on movement of a soil solute and can also carry out high-density distribution measurement. A wireless communication circuit of the wireless multipoint soil resistivity measuring system is an nRF24L01 wireless module which can form one 'one-to-many' communication network, thereby realizing multipoint measurement on the soil resistivity. The wireless multipoint soil resistivity measuring system establishes a measurement platform by a master-slave mode structure, a master machine finishes functions of receiving, processing, displaying and storing data of the soil resistivity, and a slave machine finishes functions of collecting and transmitting the data of the soil resistivity, thus a problem of consistency on multipoint soil resistivity real-time measurement is effectively solved. Based on test results, the wireless multipoint soil resistivity measuring system has excellent stability and practicability, and the soil resistivity, the saltness and the water content are of excellent linear relationship.

Description

Wireless multipoint soil resistivity measuring system
Technical field
The present invention relates to a kind of system of measuring soil resistivity, be specifically related to a kind of Wireless multipoint soil resistivity measuring system.
Background technology
21 century, agricultural reached very flourishing level, and such speed of development is mainly a large amount of uses that rely on chemical fertilizer, agricultural chemicals.These chemical substances, when bringing agricultural year, also cause the problems such as agriculture soil erosion, soil productivity decline, agricultural product and Ecological Groundwater deterioration, and agriculture sustainable development is seriously obstructed.Precision Agriculture Technology arises at the historic moment just in this case.
Precision agriculture is exactly a kind of agricultural modernization theory.So-called precision agriculture, refers to a kind of field management means based on variation.In farmland, the characteristic of field soil, crop is not homogeneous, along with time, spatial variations.And in the farmland management traditional, that still adopting at present, all think to adopt unified fertilization time, rate of fertilizer application by homogeneous.In esse difference, spatial variability make at present this mode of carrying out farm work by homogeneous have two kinds of evils: first, waste resource, in order to make the ground of barren fertilizer deficiency also can obtain high harvest, just rate of fertilizer application to be set highlyer, so original just more fertile ground has just been wasted; The second, these excessive agricultural chemicals of using, fertilizer can flow into surface water and groundwater, cause environmental pollution.Propose in this case precision agriculture, according to field, make a variation and determine that most suitable management decision, target are to reduce under the prerequisite of consumption, protection of the environment, obtaining best harvest.Precision agriculture itself is a kind of theory of sustainable development, is a kind of way to manage.
The core concept of precision agriculture is exactly the environmental factor (as soil texture, landform, fertility, water cut, disease and pest etc.) obtaining the crop yield of community, farmland and the affect plant growth otherness in room and time distribution, analyze the reason that produces these differences, take suitable regulation measure, treat with a certain discrimination, as required real-time orientation management.For the environmental factor measuring crop yield and the affect plant growth otherness in room and time distribution, directly each factor of measurement is unpractical for the agricultural of low profit, in order to reduce testing cost, in recent years people finding always one can each factor of concentrated expression index.
The optimum method of carrying out precision agriculture is exactly to supply agricultural material according to the demand of crops.The key that realizes this idea is to find out the demand of crops.According to expert's the discovery that studies for a long period of time, crops are relevant with a series of attributes of soil to the demand of agricultural material, as the resistivity of soil, water cut, compactness etc.Measure the survey instrument of the just necessary use easy to use of these attributes of soil.
Salt content, water cut, the content of organic matter, soil texture structure and the porosity isoparametric size of the resistivity of soil in can reflect soil in various degree found in research by pedology, by the spatial and temporal distributions of measuring soil resistivity and assess the growing environment of crops and the various parameters of definite soil, has great significance.
Resistivity is for representing the physical quantity of various material resistance characteristics, and unit is that ohm meter (Ω m or ohmm) represents.Soil physics research shows the abundant information that soil resistivity itself has comprised reflect soil quality and physical property.Electric current conduction in soil is produced by aperture between soil particle by moisture.Therefore, soil resistivity has following soil property to determine.
Factor of porosity: the factor of porosity of soil is larger, and resistivity is less.The soil that clay content is high has higher factor of porosity than sand.Exception, compacting meeting reduces soil resistivity conventionally.
Temperature: in the time of near temperature is reduced to freezing point, the rising that soil resistivity can be faint.When below freezing, can more and more insulate each other in soil aperture, and whole soil resistivity can sharply rise.
Water cut: dry soil is more much bigger than moist resistivity.The soil that resistivity is moderate has moderate soil texture, and maintenance moisture that can be appropriate, and the crop yield of this soil is the highest.
Salt content: the concentration that improves the electrolytic solution (salinity) in the holard can sharply reduce soil resistivity.The salt content of the soil of most of maize plantings is all very low.
Cation exchange capacity (CEC) (CEC): mineral soil comprises very high organism or about 2: 1 clay minerals all will have the ability of higher maintenance kation (as calcium, magnesium, potassium, sodium, ammonia or hydrogen) than lacking organic soil.These ions exist in the pore with soil humidity understands reduce soil resistivity the same as salinity.
The clay seam degree of depth: the resistivity response that clay presents has accurately been used on the top layer depth of soil of prediction rock-soil layer.
Soil resistivity has clear and definite correlativity except some soil attribute with above, and the relation between soil resistivity and crop yield is the focus of research always, but does not find clear and definite correlativity.
The measurement of soil resistivity is broadly divided into laboratory measurement and the large class of in-site measurement two, first laboratory measurement will prepare soil extraction, then utilize electrode method to measure the resistivity of soil extraction, utilize the variation of the measured value sign soil resistivity of soil extraction.This traditional laboratory method has higher precision as standard method of measurement, also be the benchmark of evaluating soil resistivity height, but measuring process is loaded down with trivial details, and expends the long period, real-time is poor, can not meet the requirement that modern precision agriculture requirement completes measurement in enormous quantities at short notice.
Summary of the invention
The deficiency existing in order to solve prior art, it is easy that the technical matters that the present invention solves is to provide a kind of measuring process, and expend shorter, the Wireless multipoint soil resistivity measuring system that real-time is good.Its technical scheme is:
A Wireless multipoint soil resistivity measuring system, comprises host machine part and slave part, and host machine part comprises single chip machine controlling circuit, liquid crystal display circuit, external data storage circuit, wireless communication line and keyboard circuit; Slave partly comprises single chip machine controlling circuit, wireless communication line, sine wave generating circuit, alternating constant-current source circuit, sensor electrode, difference channel, RMS-DC converter circuit, signal amplification circuit, the digital regulation resistance with AD conversion; The metering circuit part of slave produces the lower sine wave signal of degree of distortion by sine wave generating circuit, be loaded in alternating constant-current source circuit the driving source as metering circuit, be connected on two current terminals of sensor electrode, when sensor electrode connects after driving source, two voltage ends of electrode will produce voltage difference, by difference channel, obtain this difference, through RMS-DC converter circuit, obtaining the effective value direct current signal of this difference, after being amplified by amplifying circuit, pass to Chip Microcomputer A/D conversion mouthful and be AD and change.Finally by wireless module, AD transformation result is sent to main frame.
Further preferably, the single-chip microcomputer of described host machine part is STC89C52 single-chip microcomputer, and there is the programmable Timer/Counter of three 16 its inside.
Further preferably, the single-chip microcomputer self that described slave adopts is with 10,8 tunnel AD.
Further preferably, the liquid crystal display of described host machine part liquid crystal display circuit is HJ1602A graphical dots formation Liquid Crystal Module, be with backlight, Liquid Crystal Module is connected 11 I/O mouths that need to take single-chip microcomputer with single-chip microcomputer, the P3.5 of single-chip microcomputer, P3.6, P3.7 mouth are connected with RS, RW, the E of Liquid Crystal Module respectively, P2 mouth is connected with RS, RW, the E of Liquid Crystal Module, and P2 mouth is connected with the data port of Liquid Crystal Module.
Further preferably, described host machine part external data storage circuit AT24C08 adopts bus and the microcontroller communication of two-wire serial, voltage is minimum can arrive 2.5V, rated current is 1mA, quiescent current 10uA, voltage 5.5V, a 8K bit serial CMOS E2PROM, 1024 octets are contained in inside, AT24C08 has 16 byte page buffers, this device operates by I2C bus interface, AT24C08 is controlled by P0.6 mouth and the P0.7 mouth of single-chip microcomputer, R1, R2 is pull-up resistor, the data line of AT24C08 and address wire are multiplexing, adopt the mode of serial ports to transmit data, only by two line SCK shift pulses and SDA data/address and single-chip microcomputer transmission data.
Further preferably, described Wireless multipoint soil resistivity measuring system, it is characterized in that, wireless module nRF24L01 in described host machine part wireless communication line is a monolithic wireless transceiver chip that is operated in 2.4~2.5GHz ISM band, and wireless transceiver comprises: frequency generator, enhancement mode ShockBurst tMmode controller, power amplifier, crystal oscillator Oh, modulator, detuner, power stage, channel selection and agreement setting arrange by spi bus interface, the Power Management Design of nRF24L01 wireless transmit receiver module and with being connected of single-chip microcomputer, use AMS1117 stabilivolt to carry out voltage stabilizing, to obtain 3.3V burning voltage, use the P0 mouth of single-chip microcomputer to be connected with nRF24L01 wireless transmit receiver module.
Further preferably, described slave sinusoidal segment wave generation circuit adopts special purpose function signal generator ICL8038 to produce sinusoidal signal, and output signal Vsin peak-to-peak value is 5.2V, and frequency is that 330Hz output signal end Vsin will connect alternating constant current source circuit input end.
Further preferably, the modified Howland current pump circuit that described slave alternating constant-current source circuit adopts, output terminal Rsb end can ground connection, and exchange current source circuit has three parts to form, and is respectively reference source, comparison and output.The reference source Vsin of alternating current source circuit is sinusoidal signal, and this signal is produced by sine wave generating circuit, and output terminal Rsb connects load.
Further preferably, described slave difference channel differential signal input end has added voltage follower circuit.
Further preferably, described slave RMS-DC converter main circuit will consist of real effective conversion chip AD637, inside comprise active rectifier, square/divider, filter amplifier, impact damper, biasing circuit, dB OUT is level voltage output terminal, and BUFF IN, BUFF OUT are respectively input, the output terminal of impact damper.
Beneficial effect of the present invention:
(1) Wireless multipoint soil resistivity measuring system measuring process of the present invention is easy, and expends shortlyer, and real-time is good;
(2) by the passage of configuration wireless module and the communication network that channel is realized this " one-to-many ";
(3) digital regulation resistance of slave part, under the control of single-chip microcomputer, changes the output current of alternating constant current source, to adapt to the measurement of different soils;
(4) design of AT24C08 power down storage unit, AT24C08 is the electric erasable storage chip of 8KB byte, adopt bus and the microcontroller communication of two-wire serial, voltage is minimum can arrive 2.5V, rated current is 1mA, quiescent current 10uA (5.5V), and the data in chip can be preserved more than 40 years in the situation that of power-off, and adopt the DIP of 8 pin to encapsulate, easy to use;
(5) the extremely low current power dissipation of wireless communication line design: when emissive power is for-6dBm under being operated in emission mode, current drain is 9mA, is 12.3mA during receiving mode, and under power-down mode and standby mode, current drain is lower.
Accompanying drawing explanation
Fig. 1 is overall system design block diagram of the present invention;
Fig. 2 is main frame block diagram of the present invention;
Fig. 3 is slave block diagram of the present invention;
Fig. 4 is " current-voltage " four-end method schematic diagram;
Fig. 5 is main frame way circuit figure of the present invention;
Fig. 6 is wireless communication line design nRF24L01 internal logic structure figure of the present invention;
Fig. 7 is nRF24L01 Star Network structural drawing of the present invention;
Fig. 8 is slave way circuit figure of the present invention;
Fig. 9 is soil resistivity of the present invention and salt content graph of a relation;
Figure 10 is soil resistivity of the present invention and water cut graph of a relation.
Embodiment
Below in conjunction with accompanying drawing and embodiment, the present invention is described in more detail.
Overall system design block diagram is as shown in Figure 1: system adopts master-slave mode communication mode, and a main frame receives, and a plurality of slaves send.By the passage of configuration wireless module and the communication network that channel is realized this " one-to-many ".
As shown in Figure 2, be system host block diagram.It comprises single chip machine controlling circuit, liquid crystal display circuit, external data storage circuit, wireless communication line and keyboard circuit.Main frame, centered by STC89C52 single-chip microcomputer, receives to wireless module the data that slave sends and simply processes, and to identifying from plane No., then pass through liquid crystal display data.External data memory can be done regularly storage to data, so that the tracking observation to measurement point.User can realize by keyboard circuit the data manipulation of storage, as: check data, delete data, save data etc. whether automatically.
As shown in Figure 3, be slave block diagram.It comprises single chip machine controlling circuit, wireless communication line, sine wave generating circuit, alternating constant-current source circuit, sensor electrode, difference channel, RMS-DC converter circuit, signal amplification circuit, digital regulation resistance with AD conversion.The metering circuit of slave partly designs based on " current-voltage " four-end method, by sine wave generating circuit, produce the lower sine wave signal of degree of distortion, be loaded in alternating constant-current source circuit as the driving source of metering circuit, be connected on two current terminals of sensor electrode.When sensor electrode connects after driving source, two voltage ends of electrode will produce voltage difference, by difference channel, obtain this difference, through RMS-DC converter circuit, obtaining the effective value direct current signal of this difference, after being amplified by amplifying circuit, pass to Chip Microcomputer A/D conversion mouthful and be AD and change.Finally by wireless module, AD transformation result is sent to main frame.The single-chip microcomputer self adopting due to slave is with 10,8 tunnel AD, so saved extra A/D convertor circuit in circuit design.Digital regulation resistance effect is under the control of single-chip microcomputer, changes the output current of alternating constant current source, to adapt to the measurement of different soils.
Contact design based on " current-voltage " four-end method:
Contact design has used comparatively ripe " current-voltage " four-end method theoretical.The application of this theory progressively expands to farm land soil information collecting from geophysical survey, in soil resistivity is measured, is widely used.Use this theory of " current-voltage " four-end method, at measurement soil resistivity, be, can not sample, disturbed soil, can not keep the continuous coverage of ortho states original position, and measured value and soil extraction resistivity value have good correlativity simultaneously." current-voltage " four-end method, test macro comprises two current terminals and two voltage ends.Two current terminals provide measures required pumping signal, converses the resistivity of gusset material by detecting the potential difference (PD) of two voltage ends.The schematic diagram of measuring system is as shown in Figure 4:
From the definition of conductor resistance rate, if the sectional area of measuring object and length are definite, the resistivity of conductor is just easy to try to achieve.Yet for the measurement of ground resistivity, it is sectional area and length unascertainable complicated measurements all exactly
ρ = K V C - V D I = K ΔV CD I
Object.Through a large amount of scientific researches, can obtain the measurement formula of the resistivity of the earth
(1)
By computing formula, easily know, in the situation that fixed ampllitude alternate current-changing source output current is certain, soil resistivity and voltage end voltage difference are proportional.Wherein K be one with the sensor electrode relevant coefficient that distributes.
With reference to Fig. 5 main frame way circuit of the present invention figure, STC89C52 is also a low-power consumption, 8 monolithic Bigpians of high-performance CMOS include the Flash ROM (read-only memory) of erasable 1000 times repeatedly of 8kbytes ISP (In-system programable), this device adopts high density, the nonvolatile storage technologies manufacture of atmel corp, compatibility standard MCS-51 order set and 80C51 pin configuration, core Embedded general 8 central processing units and ISP Flash storage unit.
STC89C52 has following standard feature: 8k bytes Flash, 256 byte RAM, 32 I/O mouth lines, WatchDog Timer, 2 data pointers, three 16 bit timing device/counters, 2 grades of interrupt structures of one 6 vector, full duplex serial port, crystal oscillator and clock circuit in sheet.In addition, STC89C52 can be down to the operation of 0Hz static logic, supports 2 kinds of softwares can select energy-saving mode.Under idle pulley, CPU quits work, and allows RAM, timer/counter, serial ports, interruption to work on.Under power down protection mode, RAM content is saved, and oscillator is frozen, and all work of single-chip microcomputer stop, until next, interrupting or hardware reset.
Native system slave computer part is realized by single-chip microcomputer STC89C52.
The interrupt system of STC89C52 comprises six interrupt sources, is respectively:
(1) INT0-external interrupt 0 request, Low level effective.By P3.2 pin, input
(2) INT1-external interrupt 1 request, Low level effective.By P3.3 pin, input
(3) T0-timer/counter 0 overflows interrupt request
(4) T1-timer/counter 1 overflows interrupt request
(5) T2-timer/counter 2 overflows interrupt request
(6) TX/RX-serial port interrupt request
The corresponding interrupt request zone bit of each interrupt source, they are arranged in special function register TCON and SCON, and when these interrupt source requests are interrupted, the corresponding sign respectively corresponding positions in TCON and SCON latchs.The opening of interrupt source or shielding are controlled by interrupting permission register IE.
There is the programmable Timer/Counter of three 16 STC89C52 single-chip microcomputer inside, and they are all binary addition counters, when the full back to zero of counter meter, can automatically produce and overflow interrupt request, represents that timing has arrived or counted oneself and stopped.Three equal programmable of timer/counter are two kinds of timing mode and count modes, under these two kinds of patterns, all can set again four kinds of working methods, its control and state are all in corresponding special function register, by the programming to control register, just can select easily suitable working method.Timing and the counting under count mode under timing mode all can pass through program setting.By software, writing TMOD and two eight bit registers of TCON arranges the operator scheme of Timer/Counter and controls function.
(1) position of mode of operation register TMOD is defined as follows shown in table 1:
Table 1
Native system is only used the relevant knowledge of M1, M0, only introduces the function of M1, M0 pattern control bit here.
(2) four kinds of mode of operations of M1, M0 control timer T1 and timer T0 are as shown in table 2 below:
Table 2
(3) position definition and the function of control register TCON are as shown in table 3 below:
Table 3
(4) everybody effect of TCON is as follows:
TF1:T1 Overflow flag, when T1 overflows, makes interrupt flip-flop TF1 put 1 by hardware automatically, and interrupts to CPU application.
TF0:T0 Overflow flag, the same TF1 of its function situation
TR1:TI moves control bit.Can put 1 or clear 0 by software starts or closes T1
TR0:T0 moves control bit.The same TR1 of its feature operation situation
IE1: the interrupt request sign of external interrupt 1
IT1: the down trigger mode control bit of external interrupt 1
IE: the interrupt request sign of external interrupt 0
IT: the down trigger mode control bit of external interrupt 0
So that its micro-power consumption, small size, use be flexible etc., plurality of advantages obtains applying more and more widely liquid crystal display in pocket meter and low-power consumption application system.Liquid crystal display can be divided into two large classes conventionally, and a class is dot matrix type, and another kind of is character type.The common area of dot matrix type liquid crystal is larger, can display graphics; And general character mode lcd only has two row, area is little, can only show character and some very simple figures, simple and easy to control and cost is low.The current character mode lcd overwhelming majority is on the market based on HD44780 liquid crystal chip, so control principle is identical, the control program of writing for HD44780 can be applied to most character mode lcd on the market easily.
The liquid crystal display that the design adopts is HJ1602A graphical dots formation Liquid Crystal Module (being with backlight).Built-in 192 conventional characters of HJ1602A, show corresponding character by writing the ASCII character value of character.Screen can show two row, and every row shows 16 characters.
HJ1602A Liquid Crystal Module interface specification is as shown in table 4:
Table 4
VDD: positive source, 4.5-5.5V, is used 5V voltage conventionally;
V0:LCD contrast adjustment end, voltage-regulation scope is 0-5V.While connecing positive supply, contrast is the most weak, and during earthing power supply, contrast is the highest, but contrast can produce " ghost " when too high, therefore conventionally with the potentiometer of a 10K, adjusts contrast.
When RS:MCU will write instruction, making RS is low level; When MCU wants data writing, making RS is high level;
R/W: read-write control end.When R/W is high level, reading out data; When R/W is low level, data writing;
E:LCD module enable signal control end.While writing data, need negative edge trigger module.
DB0-DB7/SID:8 bit data bus, tri-state is two-way.
BLA:LED positive pole backlight.When needs are backlight, a current-limiting resistance of BLA serial connection meets VDD, BLK ground connection, and the back facet current of surveying this module is 50mA left and right;
BLK:LED holds backlightly.
HJ1602A Liquid Crystal Module instruction is as shown in table 5:
Table 5
When module is being accepted before instruction, micro-processing is along must first confirming that inside modules is in non-busy condition, and while reading BF sign, BF is required to be 0, can accept new instruction; If do not check BF sign before sending an instruction, in the middle of previous instruction and this instruction, must postpone one longer period so, be to wait for that previous instruction is really complete.
Single-chip microcomputer is followed strict sequential when communicating by letter with Liquid Crystal Module, could normally work.
[1] read states: input: RS=L, RW=H, E=H output: D0~D7 status word
[2] write command: input: RS=L, RW=L, D0~D7=order code, E=high impulse output: nothing
[3] read data: input: RS=HR, RW=H, E=H output: D0~D7=data
[4] write data: input: RS=H, RW=L, D0~D7=data, E=high impulse output: nothing
Liquid Crystal Module circuit design is mainly that the data after host process are shown, this module is connected 11 I/O mouths that need to take single-chip microcomputer with single-chip microcomputer, P3.5, the P3.6, the P3.7 mouth that are single-chip microcomputer are connected with RS, RW, the E of Liquid Crystal Module respectively, and P2 mouth is connected with the data port of Liquid Crystal Module.
Main frame external data storage circuit design: AT24C08 is a 8K bit serial CMOS E 2pROM, 1024 octets are contained in inside, and AT24C08 has 16 byte page buffers, and this device passes through I 2c bus interface operates, and has a special writing protection function.Data can be preserved and do not lost for 100 years.AT24C08 pin is described:
A0, A1, A2: address of devices is selected
SDA: serial data and/or addresses
SCL: serial clock
WP: write-protect
Vcc: power supply
Vss: ground
The design of AT24C08 power down storage unit: AT24C08 is the electric erasable storage chip of the 8KB byte of atmel corp, adopt bus and the microcontroller communication of two-wire serial, voltage is minimum can arrive 2.5V, rated current is 1mA, quiescent current 10uA (5.5V), data in chip can be preserved more than 40 years in the situation that of power-off, and adopts the DIP encapsulation of 8 pin, easy to use.
AT24C08 is controlled by P0.6 mouth and the P0.7 mouth of single-chip microcomputer, R1, R2 are pull-up resistors, its effect is the quiescent dissipation that reduces AT24C08, because data line and the address wire of AT24C08 is multiplexing, adopt the mode of serial ports to transmit data, so only use two line SCK (shift pulse) and SDA (data/address) to transmit data with single-chip microcomputer.
Wireless telecommunications are important component parts for system, and the design objective that mainly will complete is to utilize wireless module to realize networking communication function, and is applied in the multi-point sampler function of native system.
Wireless module nRF24L01 is a monolithic wireless transceiver chip of ISM band for 2.4~2.5GHz Global Access that is operated in.Wireless transceiver comprises: frequency generator, enhancement mode ShockBurst tMmode controller, power amplifier, crystal oscillator Oh, modulator, detuner.Power stage, channel selection and agreement setting can arrange by spi bus interface.
Extremely low current power dissipation: when emissive power is for-6dBm under being operated in emission mode, current drain is 9mA, is 12.3mA during receiving mode.Under power-down mode and standby mode, current drain is lower.Its major functions and features is as follows:
Enhancement mode ShockBurst tMfunction
Auto answer and automatically retransmitting function
Address and CRC check function
Wireless transmission rate: 1 or 2Mbps
SPI interface rate: 0~8Mbps
125 optional working channels
Very short time of switching channels, can be used for frequency hopping
I/O can accept the input of 5V level
Low-work voltage: 1.9~3.6V
NRF24L01 internal logic structure figure as shown in Figure 6.
NRF24L01 has mode of operation to have three kinds, and transceiver mode, idle pulley, shutdown mode and mode of operation, determined by PWR_UPregister, PRIM_RX register and CE, in Table 6.
Table 6
NRF24L01 has ShockBurst to the processing mode of packet tMwith enhancement mode ShockBurst tMtwo kinds of patterns.
ShockBurst tMunder pattern, nRF24L01 can be connected with lower-cost low speed MCU.It is the radio frequency protocol processing by chip internal that high speed signal is processed, and nRF24L01 provides SPI interface, and data transfer rate depends on the interface rate of single-chip microcomputer own.ShockBurst tMpattern, by allowing the wireless portion high-speed communication with single-chip microcomputer low-speed communication, reduces the average consumed cur-rent of communication.
At ShockBurst tMunder receiving mode, IRQ notice MCU when receiving effective address and data, MCU can read the data that receive from RX_FIFO register subsequently.
At ShockBurst tMunder sending mode, nRF24L01 generates lead code and CRC check automatically.Data are sent rear IRQ notice MCU.Reduced the query time of MCU, also just meaned that the workload that has reduced MCU has reduced the development time of software simultaneously.There are three different RX fifo registers (6 these registers of channels share) and three different TX fifo registers in nRF24L01 inside.Under power-down mode, under standby mode and in the process of data transmission, MCU can access fifo register at any time.This just allows SPI interface to carry out data transmission with low speed, and can be applied on MCU hardware, not have in the situation of SPI interface.
Enhancement mode ShockBurst tMpattern can be so that bi-directional chaining agreement be carried out more easy, effective.Typical bi-directional chaining is: transmit leg requires terminal device after receiving data, to have answer signal, so that transmit leg detects, has or not loss of data.Once loss of data, recovers the data of loss by resending function.The ShockBurst pattern of enhancement mode can be controlled simultaneously and reply and retransmitting function and without increasing MCU workload.
NRF24L01 can receive the data of the different passages in 6 tunnels under receiving mode, as shown in Figure 7.Each data channel is used different addresses, but shares identical channel.That is to say that 6 different nRF24L01 are set to can carry out communication with the same nRF24L01 that is set to receiving mode after sending mode, and the nRF24L01 that is set to receiving mode can identify to these 6 transmitting terminals.Data channel 0 is a unique data channel that can be configured to 40 self addresses.1~5 data channel is all 8 self address and 32 public address.All data channel can be set to enhancement mode ShockBurst tMpattern.
According to the feature of two kinds of data processing methods and system demand, the data processing method selective enhancement type ShockBurst of native system wireless telecommunications tMpattern.If slave number, below 6, can configure different data channel and realize networking under same channel, if slave number, more than 6, need to carry out frequency hopping, under different channels, configure respectively different data channel to expand networking quantity.
All configuration efforts of nRF2401 are all to complete by SPI, have the configuration words of 30 bytes.Native system nRF24L01 works in enhancement mode ShockBurst tMtransceiver mode, under this mode of operation, the program composition meeting of system is simpler, and stability also can be higher, therefore, below highlights nRF24L01 is configured to enhancement mode ShockBurst tMthe cell configuration method of transceiver mode.
Enhancement mode ShockBurst tMconfiguration words make nRF24L01 can process radio frequency protocol, after configuration completes, in the process of nRF24L01 work, only need to change the content in its minimum byte, to realize between receiving mode and sending mode, switch.
Enhancement mode ShockBurst tMconfiguration words can be divided into following four parts:
[1] data width: the figure place that in statement rf data bag, data take.This makes nRF24L01 can distinguish data and the CRC check code receiving in packet;
[2] address width: the figure place that in statement rf data bag, address takies.This makes nRF24L01 can distinguish address and data;
[3] address: receive the address of data, have passage 0 to the address of passage 5;
[4] CRC: make nRF24L01 can generate CRC check code and decoding.
During CRC technology in using NRF24L01 sheet, guarantee that CRC check is enabled in configuration words (EN_CRC of CONFIG), and sending and receiving is used identical agreement.
Due to what adopt in the design, be nRF24L01 wireless transmit receiver module finished product, thus only need to do nRF24L01 wireless transmit receiver module Power Management Design and with being connected of single-chip microcomputer.Because nRF24L01 wireless transmit receiver module adopts 3.3V power supply, and single-chip microcomputer adopts 5V power supply, therefore need to use AMS1117 stabilivolt to carry out voltage stabilizing, to obtain 3.3V burning voltage.Use the P0 mouth of single-chip microcomputer to be connected with nRF24L01 wireless transmit receiver module.
It with reference to Fig. 8 slave way circuit figure STC12C5608AD series monolithic, is the single-chip microcomputer of the single clock/machine cycle (1T) of macrocrystalline science and technology production, a new generation's 8051 single-chip microcomputers of high speed/low-power consumption/strong anti-interference, instruction code completely compatible traditional 8051, but speed is wanted fast 8~12 times, inner integrated MAX810 Special reset circuit.Have 10 the A/D conversions in 4 road PWM and 8 tunnels, be widely used in various electronic equipments and Industry Control occasion.
STC12C5608AD has following standard feature: 8k bytes Flash program storage area, 768 byte RAM, 23 I/O mouth lines, inner integrated MAX810 Special reset circuit, WatchDog Timer, 2 data pointers, six 16 bit timing device/counters, 2 grades of interrupt structures of one 6 vector, full duplex serial port, crystal oscillator and clock circuit in sheet.In addition, STC12C5608AD can be down to the operation of 0Hz static logic, supports 2 kinds of softwares can select energy-saving mode.Under idle pulley, CPU quits work, and allows RAM, timer/counter, serial ports, interruption to work on.Under power down protection mode, RAM content is saved, and oscillator is frozen, and all work of single-chip microcomputer stop, until next, interrupting or hardware reset.
STC12C5608AD, except possessing above-mentioned standard feature, also possesses the specific function that some are different from common 8051 single-chip microcomputers: operating frequency range 0~35MHz (being equivalent to 0~420MHz of common 8051); I/O can be arranged to four kinds of patterns, i.e. accurate bidirectional interface/weak pull-up, recommend by force/strong pull-up, only for input/high resistant, open stripping pattern formula, each I/O mouth driving force all can reach 20mA, but whole chip maximum can not surpass 55mA; ISP/IAP programming mode, without Special programming, without dedicated emulated device, can directly download by microcontroller serial port; Possess EEPROM function, can do external data memory and use; 4 road PWM/PCA; 8 10, tunnel adc circuits; SPI synchronous communication interface (master/slave pattern).
System does not have extra A/D convertor circuit, but the A/D translation function that adopts STC12C5608AD to carry realizes AD conversion.
The A/D conversion mouth of the single-chip microcomputer of STC12C5608AD serial band A/D conversion, at P1 mouth (P1.0~P1.7), has 10,8 tunnel high-speed a/d converter, and speed all can reach 100KHz (100,000 times per second).The imported A/D of 8 road voltage, can do the application such as temperature detection, voltage detecting, keyboard scan, frequency spectrum detection.After electrification reset, P1 mouth is weak pull-up type I/O mouth, and developer can arrange any road in 8 tunnels by software and be set to A/D and change, and what do not need to use as A/D mouthful can continue to use as I/O mouth.
The mouth that need to use as A/D needs to be first set to out stripping pattern formula or high resistant input, in P1M0, P1M1 register, corresponding position is arranged.Concrete configuration is shown in Table 7.
Table 7
ADC_CONTR is the A/D conversion and control register of STC12C5608AD, and its every title is in Table 8.
Table 8
Respectively everybody function of ADC_CONTR register is described below:
CHS2/CHS1/CHS0: analog input channel is selected control bit, refers to table 9.
Table 9
ADC_START: digital to analog converter conversion starts control bit, while being set to " 1 ", starts conversion, is " 0 " after EOC.
ADC_FLAG: digital to analog converter EOC zone bit, after A/D converts, ADC_FLAG=1, be by software clear 0.No matter be to be interrupted by this generation after A/D converts, or judge by software inquiry zone bit whether A/D conversion finishes, and after A/D converts, ADC_FLAG=1, must software clear 0.
SPEED1, SPEED0: digital to analog converter slewing rate control bit, refers to table 10.
Table 10
ADC_POWER:ADC power supply control bit.Be to close ADC power supply at 0 o'clock; Be to open ADC power supply at 1 o'clock.In order to guarantee high-precision A/D conversion, start after A/D conversion, before A/D EOC, try not to change the state of any I/O mouth.
A/D transformation result register has two, i.e. ADC_DATA and ADC_LOW2, and ADC_DATA is the most-significant byte of transformation result, ADC_LOW2 is the low 2 of transformation result, jointly forms 10 transformation result data.
A/D transformation result computing formula is as follows:
(ADC_DATA[7:0],ADC_LOW2[1:0])=1024×Vin/Vcc????????????(2)
Vin is analog input channel input voltage, and Vcc is single-chip microcomputer real work voltage, uses single-chip microcomputer operating voltage as analog reference voltage.If give up the low 2 of ADC_LOW2, only with 8 of ADC_DATA register, A/D transformation result is 8 to be precision, and transformation result computing formula is as follows:
ADC_DATA[7:0]=256×Vin/Vcc????????????????(3)
Sine wave generating circuit: by consulting related data, find main two kinds of sine wave generating circuit, a kind of is RC oscillatory circuit or the RL oscillatory circuit that adopts discrete elements, and another kind is the circuit that adopts integrated function generator.
Although the cost of manufacture of RC oscillatory circuit lower than the cost of function signal generator, considers sinusoidal wave low distortion and be made into power, native system design has adopted special purpose function signal generator ICL8038 to produce sinusoidal signal.
ICL8038 waveform generator is that a minimum outer member of use just can produce the monolithic integrated optical circuit of high-precision sine wave, square wave, triangular wave, sawtooth wave and pulse.The selected of frequency can select resistor or capacitor to regulate from 0.001HZ~300kHz, and frequency modulation and scanning can be completed by same external voltage.The accurate function generator of ICL8038 is the monolithic integrated circuit chip that adopts the advanced technologies such as Schottky-barrier diode to make, and output is extensively determined by temperature and change in voltage scope.This chip and phase-locked loop effect, have and when occurrence temperature changes, produce low frequency drift.The frequency of output waveform and dutycycle can also be controlled by electric current or resistance.
From ICL8038 inner structure, can find out, this chip is comprised of triangular wave oscillating circuit, comparer 1, comparer 2, trigger, triangular wave-sinusoidal wave translation circuit, constant current source CS1, CS2 etc.Constant current source CS1, CS2 are mainly used in external capacitor C to carry out charging and discharging, can utilize 4,5 pin outer meeting resistances to adjust the electric current of constant current source, to change the time constant that discharges and recharges of capacitor C, thereby change 10 pin triangle wave frequencies.Two comparers are set in 23Vs and 13Vs by internal reference voltage respectively.Two comparers must be overturn being greater than 23Vs or being less than in the scope of 13Vs.Trigger is controlled in its output simultaneously, make it control on the one hand the break-make of constant current source CS2, export on the other hand square wave through open collector impact damper, by 9 pin output square pulses, and 10 pin are directly exported triangular waves by 3 pin through impact damper, also through triangular wave-sinusoidal wave translation circuit, by 2 pin, export low-distortion sine wave in addition.External capacitor C is by two constant current source charging and electric discharge.If S disconnects, only there is electric current I 1 to C charging, when C powers on while pressing the threshold voltage 23Vs that is raised to comparer 1, trigger output Q=1.Switch S conducting, CS2 is added to the upper reverse charge of C electric current I 2, when I2 > I1, being equivalent to C is discharged by a net current I2-I1, now the upper voltage of C declines gradually, and when dropping to the threshold voltage 13Vs of comparer 2, rest-set flip-flop is reset, Q=0, so S disconnects CS2, only there is CS1 to charge to C, be so concatenated to form vibration, the upper voltage of C is approximately triangular wave, and trigger output is square wave.When the electric current of two current source CS1, CS2 is set as respectively I, 2I, equate the charging in capacitor C, discharge time, the sine wave of 10 pin triangular waves and conversion is symmetrical, and the dutycycle of square wave is 50%.If the electric current of constant current source CS1, CS2 does not meet above-mentioned relation, 3 pin are exported asymmetrical sawtooth wave, and 2 pin are exported asymmetrical sine wave, the pulse waveform that 9 pin output duty cycles are 2%~98%.Change in addition the size of constant current source I, can change the frequency of oscillator signal.
The sine wave generating circuit of native system, output signal Vsin peak-to-peak value is 5.2V, frequency is 330Hz.RP1, RP2, for regulating sinusoidal wave degree of distortion, make sinusoidal wave distortion minimum.Output signal end Vsin will connect alternating constant current source circuit input end.
Alternate current-changing source design: in " current-voltage " four-end method soil resistivity measuring principle, the measuring accuracy of soil resistivity sensor depends primarily on the precision in fixed ampllitude exchange current stream source.The exchange current source circuit of native system designs based on Howland current pump.
What conventional alternate current-changing source adopted is parallel-current negative-feedback circuit, sort circuit output voltage compliance is poor, Voltage-output efficiency is low, because sample resistance will account for voltage greatly, and conventional voltage-controlled current source can not be realized one end ground connection, and this is also the defect of parallel-current negative feedback itself.The modified Howland current pump circuit that native system adopts, has higher output voltage compliance, and output terminal Rsb end can ground connection.
According to the disconnected principle of void, have:
I o = V n R 4 + R 6 R 4 - ( V P - V i R 3 · ( R 3 + R 5 ) + V i ) / R 7 - - - ( 4 )
When R 3 R 5 = R 4 R 6 Time, have: I o = V i · R 6 R 5 + R 9 - - - ( 5 )
As can be seen from the figure regulate R7 just can change output current I o; Also be the output voltage compliance V of VCCS on the other hand lfor:
V L = V sat - R 9 · I o = V sat - V i R 6 R 4 - - - ( 6 )
V wherein satfor amplifier is the most very much not true output voltage.
Exchange current source circuit has three parts to form, and is respectively reference source, comparison and output.The reference source Vsin of alternating current source circuit is sinusoidal signal, and this signal is produced by sine wave generating circuit, and output terminal Rsb connects load.
Sample circuit R7 is connected on the output of U2A and connects with load, its resistance determines output current size, U2B and U2C form follower, by benchmark, comparison and output three part isolation, make reference voltage and output current more stable, by emulation experiment and Experiment of Electrical Circuits, prove, this circuit output current is 5uA, and output current is less than 3% with the fluctuation of load variations.
This fixed ampllitude alternate current-changing source output impedance is high, outputting current steadily, and workload-adaptability is strong.Because alternate current-changing source has automatic adjusting, this system can the large feature of adapted soil change in resistance, and does not need human intervention internal system parameter.
Difference channel design: know according to " current-voltage " four-end method, system need to detect the voltage difference between two voltage poles, i.e. Δ V cD, this just needs difference channel to realize.
Output voltage is:
u o = R f R ( u i 2 - u i 1 ) - - - ( 7 )
Work as R fduring=R,
u o=u i2-u i1????????????????????????????(8)
U wherein i1, u i2respectively two voltage pole voltages of sensor electrode, u oto connect effective value change-over circuit.
Obviously, this circuit is done when signal is adjusted and is had a serious shortcoming in prime, is exactly all less for the input resistance of each signal source, larger on the impact of signal source.Therefore, must make certain improvements to this circuit, as shown in Figure 8, be the modified difference channel that this circuit adopts.In this circuit, improved place has added voltage follower circuit at differential signal input end exactly, makes input resistance approach infinity, and output resistance is very little, and the input/output relation formula of circuit is constant.
RMS-DC converter circuit design: RMS-DC converter circuit is for converting to and have true effect to be worth equivalent direct current signal with it from difference channel output point AC signal, and real effective is one of attribute of AC signal, can react the size of AC signal.RMS-DC converter circuit in native system coordinates a small amount of outer member to form by real effective conversion chip AD637.
Real effective-direct current conversion chip that AD637 ShiAD company produces, its function is that the AC signal RMS-DC converter of outside input is become to DC signal output, can calculate the real effective of various complicated wave forms.The effective value of the input signal that can measure is up to 7V, and for the signal of 1vRMS, its three dB bandwidth is 8MHz, and can be to the level of input signal with the indication of dB form, and when applied signal voltage is 100mV, bandwidth scale value is 600kHz; When input voltage is 2V, bandwidth nominal value is 8MHz.In addition, AD637 selects the effect of (CS) pin by sheet, can make quiescent current drop to 350uA from 2.2mA.
AD637 inside comprises active rectifier (also claiming absolute value circuit); Square/divider; Filter amplifier; Impact damper; Biasing circuit.DB OUT is level voltage output terminal.BUFF IN, BUFF OUT are respectively input, the output terminal of impact damper.
The RMS-DC converter circuit that native system adopts, input signal will pass through the low-pass filter of C7 and R15 formation, for effective interchange of signal is extracted, the high frequency clutter in filtering input signal.Output terminal connects the P1.7 mouth of single-chip microcomputer and does AD conversion.Capacitor C 3 is average capacitance, and for reducing ripple signal magnitude, the size of ripple signal depends on the size of C3 and input exchange signal frequency, and at frequency input signal, fixedly in the situation that, the size of ripple signal only depends on C3.C3 is larger, and ripple is less, but that AC signal converts the time of effective value to is just longer.C4, C5 can, in the situation that ripple error is constant, shorten switching time rapidly.
System debug: concerning native system, debugging step divides following five steps to carry out:
(1) before overlap joint hardware, the LCD MODULE to Single Chip Microcomputer (SCM) system in simulation software first, button arranges module and data storage and read module and has carried out distributed simulation and whole uniting and adjustment emulation.Because the emulation of wireless data communication module in PROTEUS has certain restriction, material object debugging is carried out in this work after material object has overlapped.If the mistake of hardware components circuit diagram will be revised it, repeatedly test, until the connection of hardware is completely error-free, and reasonable in design.Whole software emulation need carry out combined debugging in PROTEUS software and KEILC51 composing software to be completed.
(2) after the hardware components of system is made.First, each module of Single Chip Microcomputer (SCM) system is carried out at length detecting debugging and assembling test, checked in manufacturing process whether have the situations such as wrong weldering, rosin joint, got rid of welding mistake.Secondly, check whether single-chip microcomputer can normally work, whether testing hardware part can complete its corresponding function.Again, according to the schematic diagram of wireless communication module design, carried out welding debugging in kind, whether test wireless module normal communication, gets rid of hard error.
(3) debugging of system slave hardware is a pith of native system debugging, comprises the debugging of offset of sinusoidal wave generation circuit, alternating constant-current source circuit, difference channel, RMS-DC converter circuit.Utilize oscillograph to observe the output signal of sine wave generating circuit, regulate two degree of distortion regulator potentiometers, make the sinusoidal signal degree of distortion of output reach minimum; Again sinusoidal signal is loaded in alternating constant-current source circuit, at constant-current source circuit output termination 30k Ω potentiometer, does load, regulator potentiometer resistance size, the situation of change of testing its output current with multimeter, more needs to improve circuit if change; The debugging of difference channel is to utilize two-way signal generator input phase identical, and whether two groups of signals that amplitude is different are that two groups of input signals are only poor by oscilloscope measurement output signal amplitude, need the resistance in circuit to do further correction if unequal.RMS-DC converter circuit is also to utilize signal generator input sinusoidal signal, and whether with multimeter, survey its output voltage is 1.41 times of input signal amplitude.By above-mentioned debug process, to guarantee that each electronic circuit of slave hardware can normally work.
(4) when the software section of design Single Chip Microcomputer (SCM) system, successively liquid-crystal data display routine, soil resistivity data acquisition program, button setting program, data recording program and Wireless Data Transmission program are debugged to several parts and carry out debugging and modification repeatedly.Reached and shown attractive in appearance, data acquisition and the reliable and stable effect of transmission.In their corresponding exploitation translation and compiling environments, program is carried out to constantly debugging compiling, until program can normally be moved.
(5) system integration and test.After four steps complete in the above, we just must partly combine the hardware and software of whole system, carry out system integration and test, can checking system normally move, and test macro property indices is seen the requirement that whether can reach expection, if desired, also to constantly revise and perfect procedure, until system can realize the function of expection, can come into operation.The system integration and test of native system is in laboratory, soil sample to be tested, open slave power supply, sensor electrode is inserted to soil, observe main frame soil resistivity value show whether stable, by button to the data of main frame check, storage and delete function test.Through above-mentioned debug process, system reaches initial design requirement substantially.
The test of system: after completing the commissioning test of whole system, by the test method that reality is suitable, test macro is demarcated, the performance index of analytic system, check its function, algorithm to realize effect and stability.Analyze and can provide the evaluation compared with science to the research of native system by experiment, for further studying foundation is provided.By following three parts, test to carry out system testing analysis:
First is distance and the stability test of Wireless Data Transmission.
Second portion is the stability test of alternating constant current source.
Third part is soil resistivity and salt content, salt content relation test.
Wireless telecommunications test: the outer open area of wireless telecommunications test locellus and two kinds, indoor obstacle place situation are tested, and are mainly the ultimate range that will determine nRF24L01 wireless module data transmission, and the foundation of implementing is installed as system.Method of testing is that slave sends character string " ABCD " to main frame in real time, if main frame can receive data, the data that receive by 1602 demonstrations, if do not received, show " abcd ".Table 11, the 12nd, the test case of two kinds of situations of outdoor open area and indoor obstacle place.
Table 11
Table 12
From table 11 and table 12, can show that the maximum effective propagation path at outdoor open area nRF24L01 is about 95m, at the maximum effective propagation path of indoor obstacle place nRF24L01, be about 75m.
Alternating constant current source stability test: one of the technological difficulties of utilization " current-voltage " four-end method measurement soil resistivity and emphasis are exactly that the alternating constant current source that is used in sensor excitation source keeps constant, stability for the fixed ampllitude alternating constant current source of detection design, utilize variable resistor simulated soil impedance variation to test, for testing the degree of stability of constant current source.
Method of testing is to increase gradually variable-resistance value, variation by oscillograph observation signal amplitude, until driving source two ends output voltage reaches the critical point of sinusoidal signal distortion, and record resistance value and the magnitude of voltage of some pilot process points and critical point, then calculate current stability error, experimental test data are as shown in table 13.
Table 13
Calculate the relative error of curent change,
r=(I max-I min)/I max·100%????????????????????(9)
Obtain r=2.63%.
Therefore, the amplitude of variation < 3% of alternating constant current source when load variations, alternating constant current source has good stability.
Soil resistivity and salt content, water cut relation test:
Soil resistivity and salt content relation test:
In order to find out the relation of soil resistivity and salt content, in indoor soil tank, keep the mass water content of soil in 15% left and right, people adds the NaCL solution of variable concentrations of equivalent to increase the salt content of soil, after salinity fully mixes with soil, insert slave sensor electrode, open main frame and receive from machine data.Keeping sensor electrode insertion depth is 5cm, and measurement data is as shown in table 14.
Table 14
According to the test data in table 14, take salt content as horizontal ordinate, soil resistivity is that ordinate is made scatter plot of data as shown in Figure 9.As can be seen from the figure, have good linear relationship between the soil resistivity that system records and salt content, salt content is higher, and the soil resistivity value recording is less.
Soil resistivity and water cut test: indoor maintenance soil salt content, in 0.15% left and right, constantly adds water to improve the water cut of soil in soil, after water and soil fully mixes, inserts sensor electrode and measures soil sample, opens slave and receives from machine data.Keeping sensor electrode insertion depth is 5cm, and measurement data is as shown in Table 15.
Table 15
According to the test data in table 14, take water cut as horizontal ordinate, soil resistivity is that ordinate is made scatter plot of data as shown in figure 10.As can be seen from the figure, have good linear relationship between the soil resistivity that system records and water cut, water cut is higher, and the soil resistivity value recording is less.

Claims (10)

1. a Wireless multipoint soil resistivity measuring system, is characterized in that, comprises host machine part and slave part, and host machine part comprises single chip machine controlling circuit, liquid crystal display circuit, external data storage circuit, wireless communication line and keyboard circuit; Slave partly comprises single chip machine controlling circuit, wireless communication line, sine wave generating circuit, alternating constant-current source circuit, sensor electrode, difference channel, RMS-DC converter circuit, signal amplification circuit, the digital regulation resistance with AD conversion; The metering circuit part of slave produces the low sine wave signal of degree of distortion by sine wave generating circuit, be loaded in alternating constant-current source circuit the driving source as metering circuit, be connected on two current terminals of sensor electrode, when sensor electrode connects after driving source, two voltage ends of electrode will produce voltage difference, by difference channel, obtain this difference, through RMS-DC converter circuit, obtaining the effective value direct current signal of this difference, after being amplified by amplifying circuit, pass to Chip Microcomputer A/D conversion mouthful and be AD and change; Finally by wireless communication line, AD transformation result is sent to main frame.
2. Wireless multipoint soil resistivity measuring system according to claim 1, is characterized in that, the single-chip microcomputer of described host machine part is STC89C52 single-chip microcomputer, and there is the programmable Timer/Counter of three 16 its inside.
3. Wireless multipoint soil resistivity measuring system according to claim 1, is characterized in that, the single-chip microcomputer self that described slave adopts is with 10,8 tunnel AD.
4. Wireless multipoint soil resistivity measuring system according to claim 2, it is characterized in that, the liquid crystal display of described host machine part liquid crystal display circuit is HJ1602A graphical dots formation Liquid Crystal Module, be with backlight, Liquid Crystal Module is connected 11 I/O mouths that need to take single-chip microcomputer with single-chip microcomputer, the P3.5 of single-chip microcomputer, P3.6, P3.7 mouth are connected with RS, RW, the E of Liquid Crystal Module respectively, and P2 mouth is connected with the data port of Liquid Crystal Module.
5. Wireless multipoint soil resistivity measuring system according to claim 2, it is characterized in that, described host machine part external data storage circuit AT24C08 adopts bus and the microcontroller communication of two-wire serial, voltage is minimum can get at 2.5V, rated current is 1mA, quiescent current 10uA, voltage 5.5V, a 8K bit serial CMOS E2PROM, 1024 octets are contained in inside, AT24C08 has 16 byte page buffers, this buffer operates by 12C bus interface, AT24C08 is controlled by P0.6 mouth and the P0.7 mouth of single-chip microcomputer, R1, R2 is pull-up resistor, the data line of AT24C08 and address wire are multiplexing, adopt the mode of serial ports to transmit data, only by two line SCK shift pulses and SDA data/address and single-chip microcomputer transmission data.
6. Wireless multipoint soil resistivity measuring system according to claim 1, it is characterized in that, wireless module nRF24L01 in described host machine part wireless communication line is a monolithic wireless transceiver chip that is operated in 2.4~2.5GHz ISM band, wireless transceiver comprises: frequency generator, enhancement mode ShockBurstTM mode controller, power amplifier, crystal oscillator, modulator, detuner, power stage, channel selection and agreement setting arrange by spi bus interface, the Power Management Design of nRF24L01 wireless transmit receiver module and with being connected of single-chip microcomputer, use AMS1117 stabilivolt to carry out voltage stabilizing, to obtain 3.3V burning voltage, use the P0 mouth of single-chip microcomputer to be connected with nRF24L01 wireless transmit receiver module.
7. Wireless multipoint soil resistivity measuring system according to claim 1, it is characterized in that, described slave sinusoidal segment wave generation circuit adopts special purpose function signal generator ICL8038 to produce sinusoidal signal, output signal Vsin peak-to-peak value is 5.2V, and frequency is that 330Hz output signal end Vsin will connect alternating constant current source circuit input end.
8. Wireless multipoint soil resistivity measuring system according to claim 1, it is characterized in that, the modified Howland current pump circuit that described slave alternating constant-current source circuit adopts, output terminal Rsb holds ground connection, alternating constant-current source circuit has three parts to form, and is respectively reference source, comparison and output, and the reference source Vsin of alternating constant-current source circuit is sinusoidal signal, this signal is produced by sine wave generating circuit, and output terminal Rsb connects load.
9. Wireless multipoint soil resistivity measuring system according to claim 1, is characterized in that, described slave difference channel differential signal input end has added voltage follower circuit.
10. Wireless multipoint soil resistivity measuring system according to claim 1, it is characterized in that, described slave RMS-DC converter main circuit will consist of real effective conversion chip AD637, inside comprise active rectifier, square/divider, filter amplifier, impact damper, biasing circuit, dB OUT is level voltage output terminal, and BUFF IN, BUFF OUT are respectively input, the output terminal of impact damper.
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