CN102426297A - Wireless multipoint soil resistivity measuring system - Google Patents

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 measured 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 mainly is a large amount of uses that rely on chemical fertilizer, agricultural chemicals.These chemical substances also cause problems such as agriculture soil erosion, soil productivity decline, agricultural product and the underground water deterioration of the ecological environment when bringing agricultural year, make the sustainable development of agricultural seriously be obstructed.The precision agriculture technology is arisen at the historic moment just in this case.

Precision agriculture is exactly the agriculture theory of a kind of modernization.So-called precision agriculture is meant a kind of field management means based on variation.The characteristic of field soil, crop is not a homogeneous in the farmland, 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 that two kinds of evils arranged: first; The waste resource; For the ground that makes barren fertilizer deficiency also can obtain high harvest, just to set rate of fertilizer application than higher, 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 underground water, cause environmental pollution.Propose precision agriculture in this case, make a variation to confirm that according to the field only management decision, target are under the prerequisite that reduces consumption, protection environment, obtain 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 to obtain crop yield of sub-district, farmland and the otherness of the environmental factor (like soil texture, landform, fertility, water cut, disease and pest etc.) that influences plant growth on room and time distributes; Analyze the reason that produces these differences; Take suitable regulation measure; Treat real-time positioning management as required with a certain discrimination.In order to measure crop yield and the otherness of the environmental factor that influences plant growth on room and time distributes; Directly measuring each factor is unpractical for the agricultural of hanging down profit; In order to reduce the detection cost, in recent years people seeking 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.Realize that the key of 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, like the resistivity of soil, water cut, compactness etc.Want the survey instrument of the just necessary use easy to use of these attributes of measured soil.

Through salt content, water cut, the content of organic matter, soil texture structure and the isoparametric size of porosity in can reflection soil in various degree to the resistivity of discovering soil of pedology, the spatial and temporal distributions of various parameters of assessing growing environment and the definite soil of crops by measured soil resistivity has great significance.

Resistivity is the physical quantity that is used for representing various material resistance characteristics, and unit is ohm meter (Ω m or ohmm) expression.Soil physics research shows that soil resistivity itself has comprised the abundant information of reflection soil quality and physical property.Conduction of current in the soil is produced through aperture between the soil particle by moisture.Therefore, soil resistivity has following soil property to determine.

Factor of porosity: the factor of porosity of soil is big more, and resistivity is more little.The soil that clay content is high has higher factor of porosity than sand.What make an exception is that the compacting meeting reduces soil resistivity usually.

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 the 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 can the appropriateness maintenance moisture, 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 (like calcium, magnesium, potassium, sodium, ammonia or hydrogen) than lacking organic soil.These ions exist with the moist pore of soil in understand the same soil resistivity that reduces with salinity.

The clay seam degree of depth: the resistivity response that clay appears accurately has been used on the top layer depth of soil of prediction rock-soil layer.

Soil resistivity is except having the clear and definite correlativity with some top soil attribute, and the relation between soil resistivity and the 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 in-site measurement two big classes; Laboratory measurement at first will prepare soil extraction; Utilize the resistivity of electrode method measured soil leaching liquor then, 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 estimating the soil resistivity height, but measuring process is loaded down with trivial details, and expends the long period; Real-time is poor, can not satisfy modern precision agriculture requirement and accomplish Testing requirement in enormous quantities at short notice.

Summary of the invention

In order to solve the deficiency that prior art exists, it is easy that the technical matters that the present invention solves provides 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 kind of 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, effective value change-over circuit, signal amplification circuit, the digital regulation resistance of band 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 on the alternating constant-current source circuit as the driving source of metering circuit, be connected on two current terminals of sensor electrode, after sensor electrode connects driving source; Two voltage ends of electrode will produce voltage difference; Obtain this difference by difference channel,, do the AD conversion by passing to Chip Microcomputer A conversion mouth after the amplifying circuit amplification at the effective value direct current signal that obtains this difference through the effective value change-over circuit.Through wireless module the AD transformation result is sent to main frame at last.

Further preferred, the single-chip microcomputer of said host machine part is the STC89C52 single-chip microcomputer, and there is three 16 programmable Timer its inside.

Further preferred, the singlechip that said slave adopts has 8 tunnel 10 AD.

Further preferred; The liquid crystal display of said host machine part liquid crystal display circuit is a HJ1602A graphical dots formation Liquid Crystal Module; Be with backlightly, Liquid Crystal Module is connected 11 I/O mouths that need take single-chip microcomputer with single-chip microcomputer, and the P3.5 of single-chip microcomputer, P3.6, P3.7 mouth link to each other with RS, RW, the E of Liquid Crystal Module respectively; The P2 mouth links to each other with RS, RW, the E of Liquid Crystal Module, and the P2 mouth links to each other with the data port of Liquid Crystal Module.

Further preferred, said host machine part external data storage circuit AT24C08 adopts the bus and the microcontroller communication of two-wire serial, and voltage is minimum can to arrive 2.5V; Rated current is 1mA, quiescent current 10uA, voltage 5.5V; Be a 8K bit serial CMOS E2PROM, 1024 octets are contained in inside, and AT24C08 has one 16 byte page buffer; This device is operated through the I2C EBI, and AT24C08 is by the P0.6 mouth and the control of P0.7 mouth of single-chip microcomputer, and R1, R2 are pull-up resistors; The data line of AT24C08 and address wire are multiplexing, adopt the mode of serial ports to transmit data, only with two line SCK shift pulses and SDA data/address and single-chip microcomputer transmission data.

Further preferred; Described wireless multipoint soil resistivity measuring system; It is characterized in that; Wireless module nRF24L01 in the said 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 output, channel selection and agreement setting are provided with through the spi bus interface; The design of the power supply of nRF24L01 wireless transmit receiver module with being connected of single-chip microcomputer; Use the AMS1117 stabilivolt to carry out voltage stabilizing,, use the P0 mouth of single-chip microcomputer to be connected with nRF24L01 wireless transmit receiver module to obtain the 3.3V burning voltage.

Further preferred, said 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 preferred, the modified Howland current pump circuit that said slave alternating constant-current source circuit adopts, output terminal Rsb end can ground connection, and the exchange current source circuit has three parts to constitute, and is respectively reference source, comparison and output.The reference source Vsin of alternating current source circuit is a sinusoidal signal, and this signal is produced by sine wave generating circuit, and output terminal Rsb connects load.

Further preferred, said slave difference channel differential signal input end has added voltage follower circuit.

Further preferred; Said slave effective value change-over circuit mainly is made up of real effective conversion chip AD637; Inside comprise active rectifier, square/divider, filter amplifier, impact damper, biasing circuit; DB OUT is the 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) through 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 changes the output current in alternating constant-current source, to adapt to the measurement of different soils under the control of single-chip microcomputer;

(4) design of AT24C08 power down storage unit, AT24C08 is the electric erasable storage chip of 8KB byte, adopts the bus and the microcontroller communication of two-wire serial; Voltage is minimum can to arrive 2.5V; Rated current is 1mA, and the data in the quiescent current 10uA (5.5V), chip can be preserved more than 40 years under the situation of outage; And adopt the DIP of 8 pin to encapsulate, easy to use;

(5) the extremely low current power dissipation of wireless communication line design: current drain was 9mA when emissive power was for-6dBm under being operated in emission mode, was 12.3mA during receiving mode, and current drain is lower under power-down mode and the standby mode.

Description of drawings

Fig. 1 is an overall system design block diagram of the present invention;

Fig. 2 is a main frame block diagram of the present invention;

Fig. 3 is a 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 a 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 done explanation in further detail.

The overall system design block diagram is as shown in Figure 1: system adopts the master-slave mode communication mode, and promptly a main frame receives, and a plurality of slaves send.Through the passage of configuration wireless module and the communication network that channel is realized this " one-to-many ".

As shown in Figure 2, be the 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 is the center with the STC89C52 single-chip microcomputer, wireless module is received the data that slave sends simply handle, and to doing identification from plane No., pass through liquid crystal display data then.External data memory can be done regularly storage to data, so that to the tracking observation of measurement point.The user to the storage data manipulation can realize through keyboard circuit, as: check data, deleted data, whether preserve data etc. automatically.

As shown in Figure 3, be the 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, effective value change-over circuit, signal amplification circuit, the digital regulation resistance of band AD conversion.The metering circuit of slave partly is based on the design of " current-voltage " four-end method; Produce the lower sine wave signal of degree of distortion by sine wave generating circuit; Be loaded on the alternating constant-current source circuit as the driving source of metering circuit, be connected on two current terminals of sensor electrode.After sensor electrode connects driving source; Two voltage ends of electrode will produce voltage difference; Obtain this difference by difference channel,, do the AD conversion by passing to Chip Microcomputer A conversion mouth after the amplifying circuit amplification at the effective value direct current signal that obtains this difference through the effective value change-over circuit.Through wireless module the AD transformation result is sent to main frame at last.Because the singlechip that slave adopts has 8 tunnel 10 AD, so saved extra A/D convertor circuit on the circuit design.The digital regulation resistance effect is under the control of single-chip microcomputer, changes the output current in alternating constant-current source, to adapt to the measurement of different soils.

Contact design based on " current-voltage " four-end method:

The contact design has used comparatively ripe " current-voltage " four-end method theoretical.The application of this theory progressively expands to the farm land soil information collecting from geophysical survey, in soil resistivity is measured, has obtained using widely.This theory of utilization " current-voltage " four-end method, in measured soil resistivity be, can not take a sample, the not disturbance soil body can keep the continuous coverage of ortho states original position, and measured value and soil extraction resistivity value have correlativity preferably simultaneously." current-voltage " four-end method, promptly test macro comprises two current terminals and two voltage ends.Two current terminals provide measures required pumping signal, converses the resistivity of gusset material through the potential difference (PD) that detects two voltage ends.Measuring principle of measurement system figure is as shown in Figure 4:

Definition by the conductor resistance rate can be known, if the sectional area of measuring object and length confirm that then the resistivity of conductor just is easy to try to achieve.Yet for the measurement of ground resistivity, it is sectional area and all unascertainable complicated measurement of length exactly

$\mathrm{\ρ}=K\frac{V_C-V_D}{I}=K\frac{{\mathrm{\ΔV}}_{\mathrm{CD}}}{I}$

Object.Through a large amount of scientific researches, can obtain the measurement formula of the resistivity of the earth

(1)

Know easily that through computing formula under the certain situation of fixed ampllitude alternate current-changing source output current, 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 also is a low-power consumption; 8 single-chip microcomputer sheets of high-performance CMOS include 8kbytes ISP (In-system programable) can be erasable repeatedly 1000 times the Flash ROM (read-only memory); This device adopts high density, the nonvolatile storage technologies manufacturing of atmel corp, compatibility standard MCS-51 order set and 80C51 pin configuration, integrated general 8 central processing units and ISP Flash storage unit in the chip.

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, crystal oscillator and clock circuit in the full duplex serial port, sheet.In addition, STC89C52 can reduce to the operation of 0Hz static logic, supports 2 kinds of softwares can select energy-saving mode.Under the idle pulley, CPU quits work, and allows RAM, timer/counter, serial ports, interruption to work on.Under the power down protection mode, the RAM content is preserved, and oscillator is freezed, and all work of single-chip microcomputer stop, till next one interruption 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 is effective.Import through the P3.2 pin

(2) INT1-external interrupt 1 request, low level is effective.Import through the P3.3 pin

(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 all corresponding interrupt request zone bit of each interrupt source, they are arranged among special function register TCON and the SCON, and when these interrupt source requests were interrupted, corresponding sign was latched by the corresponding positions among TCON and the SCON respectively.Opening or shielding to interrupt source are controlled by interrupting permission register IE.

There is three 16 programmable Timer STC89C52 single-chip microcomputer inside, and they all are binary addition counters, when the counter meter completely returns zero, can produce automatically and overflow interrupt request, and the expression 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 four kinds of working methods again; Its control and state are all in corresponding special function register; Through programming, just can select suitable working method easily to control register.Timing and the counting under the count mode under the timing mode all can pass through program setting.Write operator scheme and the control function that TMOD and two eight bit registers of TCON are provided with Timer through software.

(1) the position definition of mode of operation register TMOD is as shown in table 1 below:

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 following:

TF1:T1 overflow indicator position when T1 overflows, makes interrupt flip-flop TF1 put 1 by hardware automatically, and interrupts to the CPU application.

TF0:T0 overflow indicator position, the same TF1 of its function situation

TR1:TI moves control bit.Can put 1 or clear 0 through 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

Plurality of advantages obtains application more and more widely to LCD in pocket meter and low-power consumption application system so that its little power consumption, small size, use be flexible etc.LCD can be divided into two big types usually, and one type is dot matrix type, and another kind of is character type.The common area of dot matrix type liquid crystal is bigger, can display graphics; And general character mode lcd has only two row, and area is little, can only character display and some very simple figures, and simple and easy to control and cost is low.The present character mode lcd overwhelming majority on the market is based on the HD44780 liquid crystal chip, so control principle is identical, the control program of writing for HD44780 can be applied to most on the market character mode lcd easily.

The liquid crystal display that the design adopts is a HJ1602A graphical dots formation Liquid Crystal Module (being with backlight).Built-in 192 conventional characters of HJ1602A show corresponding character through the ASCII character value that writes 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 uses 5V voltage usually;

V0:LCD contrast adjustment end, voltage-regulation scope are 0-5V.When connecing positive supply contrast a little less than, contrast is the highest during earthing power supply, but contrast can produce " ghost " when too high, therefore uses the potentiometer of a 10K to adjust contrast usually.

When RS:MCU will write instruction, making RS was low level; When MCU will write data, making RS was high level;

R/W: read-write control end.When R/W is high level, reading of data; When R/W is low level, write data;

E:LCD module enable signal control end.During write data, need the negative edge trigger module.

The DB0-DB7/SID:8 bit data bus, ternary two-way.

BLA:LED positive pole backlight.When needs were backlight, current-limiting resistance of BLA serial connection met VDD, BLK ground connection, and the back facet current of surveying this module is about 50mA;

BLK:LED holds backlightly.

HJ1602A Liquid Crystal Module instruction is as shown in table 5:

Table 5

Before module was being accepted instruction, little processing was along confirming that earlier inside modules is in non-busy condition, and BF is required to be 0 when promptly reading the BF sign, can accept new instruction; If before seeing an instruction off, do not check the BF sign, in the middle of previous instruction and this instruction, must postpone one section so than the long time, promptly be to wait for that previous instruction is complete really.

Single-chip microcomputer is followed strict sequential with Liquid Crystal Module when communicating by letter, could operate as normal.

[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: do not have

[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: do not have

The Liquid Crystal Module circuit design mainly is that the data presentation after the host process is come out; This module is connected 11 I/O mouths that need take single-chip microcomputer with single-chip microcomputer; The P3.5, P3.6, the P3.7 mouth that are single-chip microcomputer link to each other with RS, RW, the E of Liquid Crystal Module respectively, and the P2 mouth links to each other 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 one 16 byte page buffer, and this device passes through I ²The C EBI is operated, and a special write-protect function is arranged.Data can be preserved and do not lost in 100 years.The AT24C08 pin is described:

A0, A1, A2: address of devices is selected

SDA: serial data and

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 the bus and the microcontroller communication of two-wire serial, voltage is minimum can to arrive 2.5V, and rated current is 1mA; Quiescent current 10uA (5.5V); Data in the chip can be preserved more than 40 years under the situation of outage, and adopts the DIP encapsulation of 8 pin, and is easy to use.

AT24C08 is by the P0.6 mouth and the control of 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 are 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 of system design, and the design objective that mainly will accomplish is to utilize wireless module to realize the networking communication function, and is applied in the multi-point sampler function of native system.

Wireless module nRF24L01 is a monolithic wireless transceiver chip that is operated in 2.4～2.5GHz Global Access with ISM band.Wireless transceiver comprises: frequency generator, enhancement mode ShockBurst ^TMMode controller, power amplifier, crystal oscillator Oh, modulator, detuner.Power output, channel selection and agreement setting can be provided with through the spi bus interface.

Extremely low current power dissipation: current drain was 9mA when emissive power was for-6dBm under being operated in emission mode, was 12.3mA during receiving mode.Current drain is lower under power-down mode and the standby mode.Its major functions and features is following:

Enhancement mode ShockBurst ^TMFunction

Auto answer and automatic retransmitting function

Address and CRC check function

Wireless transmission rate: 1 or 2Mbps

SPI interface rate: 0～8Mbps

125 optional working channels

Very short channel switching time, can be used for frequency hopping

I/O can accept the input of 5V level

Low-work voltage: 1.9～3.6V

Figure is as shown in Figure 6 for the nRF24L01 internal logic structure.

NRF24L01 has mode of operation to have three kinds, and promptly transceiver mode, idle pulley, shutdown mode and mode of operation by PWR_UPregister, PRIM_RX register and CE decision, are seen table 6.

Table 6

NRF24L01 has ShockBurst to the processing mode of packet ^TMWith enhancement mode ShockBurst ^TMTwo kinds of patterns.

ShockBurst ^TMNRF24L01 can link to each other with lower-cost low speed MCU under the pattern.It is the radio frequency protocol processing by chip internal that high speed signal is handled, and nRF24L01 provides SPI interface, and data transfer rate depends on the interface rate of single-chip microcomputer own.ShockBurst ^TMPattern is through allowing the wireless portion high-speed communication with the single-chip microcomputer low-speed communication, the average consumed cur-rent that reduces to communicate by letter.

At ShockBurst ^TMUnder the receiving mode, IRQ notice MCU when receiving effective address and data, MCU can read the data that receive from the RX_FIFO register subsequently.

At ShockBurst ^TMUnder the sending mode, nRF24L01 generates lead code and CRC check automatically.Data are sent the back IRQ notice MCU that finishes.Reduced the query time of MCU, just meaned that also the workload that has reduced MCU has reduced the Development of Software time simultaneously.There is three different RX fifo registers (6 these registers of channels share) TX fifo register different with three nRF24L01 inside.MCU can visit fifo register at any time under power-down mode, under the standby mode and in the process of data transmission.This just allows the SPI interface to carry out the data transmission with low speed, and can be applied to not have on the MCU hardware under the situation of SPI interface.

Enhancement mode ShockBurst ^TMPattern can so that the bi-directional chaining agreement carry out more easy, effectively.Typical bi-directional chaining is: transmit leg requires terminal device that answer signal is arranged after receiving data, so that transmit leg detects no data loss is arranged.In case loss of data is then through resending the data recovery that function will be lost.The ShockBurst pattern of enhancement mode can be controlled simultaneously and reply and retransmitting function and need not to increase the MCU workload.

NRF24L01 can receive the data of 6 tunnel different passages under receiving mode, as shown in Figure 7.Each data channel is used different address, but shared 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 behind the sending mode, and the nRF24L01 that is set to receiving mode can discern 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 all is 8 self address and 32 public address.All data channel can be set to enhancement mode ShockBurst ^TMPattern.

According to the characteristics and the system design demand of two kinds of data processing methods, the data processing method of native system wireless telecommunications is selected enhancement mode ShockBurst ^TMPattern.If the slave number, then can dispose different data channel below 6 and realize networking under same channel,, under different frequency channels, dispose different data channel respectively to enlarge networking quantity if the slave number more than 6, need carry out frequency hopping.

All configuration efforts of nRF2401 all are to accomplish through 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, and therefore, hereinafter highlights and is configured to enhancement mode ShockBurst to nRF24L01 ^TMThe cell configuration method of transceiver mode.

Enhancement mode ShockBurst ^TMConfiguration words make nRF24L01 can handle radio frequency protocol, after configuration is accomplished, in the process of nRF24L01 work, only need to change the content in its minimum byte, switch between receiving mode and the sending mode realizing.

Enhancement mode ShockBurst ^TMConfiguration words can be divided into following four parts:

[1] data width: the figure place of data occupancy in the statement rf data bag.This makes nRF24L01 can distinguish data and the CRC check sign indicating number that receives in the packet;

[2] address width: the figure place that the address takies in the statement rf data bag.This makes nRF24L01 can distinguish address and data;

[3] address: receive the address of data, the address of passage 0 to passage 5 arranged;

[4] CRC: make nRF24L01 can generate CRC check sign indicating number and decoding.

When the CRC in using the NRF24L01 sheet is technological, guarantee that CRC check is enabled in configuration words (EN_CRC of CONFIG), and send with receiving and use identical agreement.

Because what adopt among the design is nRF24L01 wireless transmit receiver module finished product, thus the power supply design that only need do nRF24L01 wireless transmit receiver module with being connected of single-chip microcomputer.Because nRF24L01 wireless transmit receiver module adopts the 3.3V power supply, and single-chip microcomputer adopts the 5V power supply, therefore needs to use the AMS1117 stabilivolt to carry out voltage stabilizing, to obtain the 3.3V burning voltage.Use the P0 mouth of single-chip microcomputer to be connected with nRF24L01 wireless transmit receiver module.

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; Be high speed/low-power consumption/strong jamproof 8051 single-chip microcomputers of new generation; Instruction code fully compatible traditional 8051; But speed is wanted fast 8～12 times, the special-purpose reset circuit of inner integrated MAX810.Have 4 road PWM and 8 tunnel 10 A/D conversions, 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; The special-purpose reset circuit of inner integrated MAX810, WatchDog Timer, 2 data pointers; Six 16 bit timing device/counters; 2 grades of interrupt structures of one 6 vector, crystal oscillator and clock circuit in the full duplex serial port, sheet.In addition, STC12C5608AD can reduce to the operation of 0Hz static logic, supports 2 kinds of softwares can select energy-saving mode.Under the idle pulley, CPU quits work, and allows RAM, timer/counter, serial ports, interruption to work on.Under the power down protection mode, the RAM content is preserved, and oscillator is freezed, and all work of single-chip microcomputer stop, till next one interruption or hardware reset.

STC12C5608AD also possesses the specific function that some are different from common 8051 single-chip microcomputers except possessing above-mentioned standard feature: operating frequency range 0～35MHz (be equivalent to common 8051 0～420MHz); I/O can be arranged to four kinds of patterns, draws, recommends by force on the promptly accurate bidirectional interface/weak/Qiang Shangla, is merely input/high resistant, opens the stripping pattern formula, and each I/O mouth driving force all can reach 20mA, but the entire chip maximum can not surpass 55mA; The ISP/IAP programming mode need not special-purpose programmable device, need not dedicated emulated device, can directly download through microcontroller serial port; Possess the EEPROM function, can do external data memory and use; 4 road PWM/PCA; 8 tunnel 10 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 the AD conversion.

(P1.0～P1.7), 8 tunnel 10 high-speed a/d converters are arranged, speed all can reach 100KHz (100,000 per seconds) to the A/D conversion mouth of the single-chip microcomputer of STC12C5608AD series band A/D conversion at the P1 mouth.The imported A/D of 8 road voltages can do application such as temperature detection, voltage detecting, keyboard scan, frequency spectrum detection.The P1 mouth is the weak pull-up I/O mouth of behind the electrification reset, and the developer can be set to the A/D conversion with any one tunnel in 8 tunnel through software setting, need mouthful can not continue to use as the I/O mouth as what A/D used.

It is set to out stripping pattern formula or high resistant input need to need elder generation as the mouth that A/D uses, and in P1M0, P1M1 register, corresponding position is provided with.Concrete configuration is seen shown in the table 7.

Table 7

ADC_CONTR is the A/D conversion and control register of STC12C5608AD, and its every title is seen table 8.

Table 8

Respectively everybody function of ADC_CONTR register is described below:

CHS2/CHS1/CHS0: analog input channel is selected control bit, sees table 9 for details.

Table 9

ADC_START: digital to analog converter conversion start-up control position, when being set to " 1 ", begin conversion, behind the EOC be " 0 ".

ADC_FLAG: digital to analog converter EOC zone bit, after A/D converted, ADC_FLAG=1 will be by software clear 0.No matter be that A/D converts the back by this generation interruption, still judge by the software query zone bit whether the A/D conversion finishes, and after A/D converted, ADC_FLAG=1 must software clear 0.

SPEED1, SPEED0: digital to analog converter slewing rate control bit, see table 10 for details.

Table 10

ADC_POWER:ADC power supply control bit.Be to close the ADC power supply at 0 o'clock; It is 1 o'clock unlatching ADC power supply.In order to guarantee high-precision A/D conversion, after the startup A/D conversion, before the 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 low 2 of transformation result, forms 10 transformation result data jointly.

A/D transformation result computing formula is following:

(ADC_DATA[7:0]，ADC_LOW2[1:0])＝1024×Vin/Vcc (2)

Vin is the analog input channel input voltage, and Vcc is a single-chip microcomputer real work voltage, with the single-chip microcomputer WV as analog reference voltage.If give up the low 2 of ADC_LOW2, only with 8 of ADC_DATA register, then the A/D transformation result is 8 to be precision, and the transformation result computing formula is following:

ADC_DATA[7:0]＝256×Vin/Vcc (3)

Sine wave generating circuit: through 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 is lower than the cost of function signal generator, consider sinusoidal wave low distortion and be made into power that the native system design has adopted special purpose function signal generator ICL8038 to produce sinusoidal signal.

The ICL8038 waveform generator is that a minimum outer member of usefulness 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 for use resistor or capacitor to regulate from 0.001HZ～300kHz, and frequency modulation and scanning can be accomplished by same external voltage.The accurate function generator of ICL8038 is the monolithic integrated circuit chip that adopts advanced technologies such as Schottky-barrier diode to process, and output is extensively determined by temperature and change in voltage scope.This chip and the effect of phaselocked loop loop have the low frequency drift of generation when occurrence temperature changes.The frequency of output waveform and dutycycle can also be by electric current or resistance controls.

Can find out that from the ICL8038 inner structure this chip is made up 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 are carried out charging and discharging, and the electric current of 4,5 pin outer meeting resistances adjustment constant current source capable of using with the time constant that discharges and recharges of change capacitor C, thereby changes 10 pin triangle wave frequencies.Two comparers are set in 23Vs and 13Vs by internal reference voltage respectively.Two comparers must be overturn in greater than 23Vs or the scope less than 13Vs.Trigger is controlled in its output simultaneously; Make it control the break-make of constant current source CS2 on the one hand; Export square wave on the other hand through the open collector impact damper; By 9 pin output square pulse, and 10 pin are directly exported triangular wave by 3 pin through impact damper, also export low-distortion sine wave through triangular wave-sinusoidal wave translation circuit by 2 pin in addition.External capacitor C is by two constant current source charging and discharge.If S breaks off, electric current I 1 is only arranged to the C charging, when C powers on when pressing the threshold voltage 23Vs that is raised to comparer 1 trigger output Q=1.The switch S conducting, CS2 is added to C to electric current I 2 and goes up reverse charge, when I2＞I1, is equivalent to C and is discharged by a net current I2-I1; The last voltage of C this moment descends gradually, and when dropping to the threshold voltage 13Vs of comparer 2, rest-set flip-flop is reset; Q=0 so S breaks off CS2, only has CS1 that C is charged; So be concatenated to form vibration, the last voltage of C is approximately triangular wave, and trigger output then is square wave.When the electric current of two current source CS1, CS2 was set at I, 2I respectively, the charging on the capacitor C, discharge time equated that then 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 satisfy above-mentioned relation, then 3 pin are exported asymmetrical sawtooth wave, and 2 pin are exported asymmetrical sine wave, and 9 pin output duty cycles are 2%～98% pulse waveform.Change the size of constant current source I in addition, 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 are used to regulate sinusoidal wave degree of distortion, make sinusoidal wave distortion minimum.Output signal end Vsin will connect alternating constant-current source circuit input end.

The 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 is based on the design of Howland current pump.

What conventional alternate current-changing source adopted is the parallel-current negative-feedback circuit; Sort circuit output voltage compliance is relatively poor; The voltage output efficiency is low; Because sample resistance will account for greatly voltage, and conventional voltage-controlled current source can not realize an end ground connection, and this also is the defective of parallel-current negative feedback itself.The modified Howland current pump circuit that native system adopted has higher output voltage compliance, and output terminal Rsb end can ground connection.

Have according to the disconnected principle of void:

$I_o={\mathrm{<figure-callout\; id="4"\; label="V\; n\; R"\; filenames="HSA00000558046300022.png,HSA00000558046300032.png"\; state="\{\{state\}\}">V</figure-callout>}}_n\frac{R_{}}{}\frac{{}_4+R_6}{R_4}-(\frac{V_P-V_i}{R_3}\&CenterDot;({\mathrm{<figure-callout\; id="3"\; label="R"\; filenames="HSA00000558046300022.png,HSA00000558046300032.png"\; state="\{\{state\}\}">R</figure-callout>}}_3+R_5)+V_i)/R_7---\left(4\right)$

When $\frac{R_3}{{\mathrm{<figure-callout\; id="5"\; label="R"\; filenames="HSA00000558046300022.png,HSA00000558046300041.png"\; state="\{\{state\}\}">R</figure-callout>}}_5}=\frac{R_4}{{\mathrm{<figure-callout\; id="6"\; label="R"\; filenames="HSA00000558046300022.png,HSA00000558046300041.png"\; state="\{\{state\}\}">R</figure-callout>}}_6}$ The time, then have: $I_o=V_i\&CenterDot;\frac{R_6}{{\mathrm{<figure-callout\; id="5"\; label="R"\; filenames="HSA00000558046300022.png,HSA00000558046300041.png"\; state="\{\{state\}\}">R</figure-callout>}}_5+R_9}---\left(5\right)$

As can be seen from the figure regulate R7 and just can change output current I _oAlso be the output voltage compliance V of VCCS on the other hand _LFor:

$V_L=V_{\mathrm{sat}}-{\mathrm{<figure-callout\; id="9"\; label="R"\; filenames="HSA00000558046300022.png,HSA00000558046300041.png"\; state="\{\{state\}\}">R</figure-callout>}}_9\&CenterDot;I_o=V_{\mathrm{sat}}-V_i\frac{R_6}{R_4}---\left(6\right)$

V wherein _SatFor amplifier the most very much not is true output voltage.

The exchange current source circuit has three parts to constitute, and is respectively reference source, comparison and output.The reference source Vsin of alternating current source circuit is a 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 decision output current size, U2B and U2C constitute follower, and benchmark, comparison and output three parts are isolated; Make reference voltage and output current more stable; Prove that through emulation experiment and Experiment of Electrical Circuits this circuit output current is 5uA, and output current with the fluctuation of load variations less than 3%.

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 self-regulating characteristics, this system can the big characteristics of adapted soil change in resistance, and do not need human intervention internal system parameter.

Difference channel design: know that according to " current-voltage " four-end method system need detect the voltage difference between two voltage poles, i.e. Δ V _CD, this just needs difference channel to realize.

Output voltage is:

$u_o=\frac{R_f}{R}(u_{i2}-u_{i1})---\left(7\right)$

Work as R _fDuring=R,

u _o＝u _i2-u _i1 (8)

U wherein _I1, u _I2Be respectively two voltage pole voltages of sensor electrode, u _oTo connect the effective value change-over circuit.

Obviously, there is an important disadvantages in this circuit when prime is done the signal adjustment, be exactly all less for the input resistance of each signal source, and is bigger to the influence 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.Improved place has added voltage follower circuit at the differential signal input end exactly in this circuit, makes the input resistance approach infinity, and output resistance is very little, and the input/output relation formula of circuit is constant.

The design of effective value change-over circuit: the effective value change-over circuit is used for converting to from difference channel output point AC signal with it equivalent direct current signal of true effect value being arranged, and real effective is one of attribute of AC signal, can react the size of AC signal.Effective value change-over circuit in the native system cooperates the small number of external element to constitute by real effective conversion chip AD637.

AD637 is real effective-direct current conversion chip that AD company produces, and its function is to convert the AC signal effective value of outside input to direct current 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 indicate with the dB form the level of input signal, and when applied signal voltage was 100mV, the bandwidth scale value was 600kHz; When input voltage was 2V, the bandwidth nominal value was 8MHz.In addition, AD637 can make quiescent current drop to 350uA from 2.2mA through the effect of sheet choosing (CS) pin.

AD637 inside comprises active rectifier (also claiming absolute value circuit); Square/divider; Filter amplifier; Impact damper; Biasing circuit.DB OUT is the level voltage output terminal.BUFF IN, BUFF OUT are respectively input, the output terminal of impact damper.

The effective value change-over circuit that native system adopts, input signal will pass through the low-pass filter of C7 and R15 formation, are used for effective interchange of signal being extracted the high frequency clutter in the filtering input signal.Output terminal connects the P1.7 mouth of single-chip microcomputer and does the AD conversion.Capacitor C 3 is an average capacitance, is used to reduce the ripple signal magnitude, and the size of ripple signal depends on the size of C3 and input exchange signal frequency, and under the situation that frequency input signal is fixed, the size of ripple signal only depends on C3.C3 is big more, and ripple is more little, but that AC signal converts the time of effective value to is just long more.C4, C5 can shorten switching time rapidly under the constant situation of ripple error.

System debug: concerning native system, five steps below debugging step divides carry out:

(1) the overlap joint hardware before, at first in simulation software to the LCD MODULE of SCM system, button is provided with module and data storage and read module and has carried out distributed simulation and whole uniting and adjustment emulation.Because the emulation of RFDC module in PROTEUS has certain restriction, the material object debugging is carried out in this work after the material object overlap joint is accomplished.If the mistake of hardware components circuit diagram then will be revised it, test is error-free fully up to the connection of hardware repeatedly, and reasonable in design.Whole software emulation needs in PROTEUS software and KEILC51 composing software, to carry out combined debugging and accomplishes.

(2) after the hardware components of system is made.At first, each module of SCM system is carried out at length detecting debugging and assembling test, checked situation such as whether having wrong weldering, rosin joint in the manufacturing process, got rid of the welding mistake.Secondly, check that single-chip microcomputer whether can operate as normal, whether the testing hardware part can accomplish its function corresponding.Once more, carried out welding debugging in kind according to the schematic diagram of wireless communication module design, whether the test wireless module normal communication, gets rid of hard error.

(3) debugging of system's 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, effective value change-over 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; Sinusoidal signal is loaded on the alternating constant-current source circuit again, does load at constant-current source circuit output termination 30k Ω potentiometer, regulator potentiometer resistance size with the situation of change of its output current of multimeter test, more then need be improved circuit if change; The debugging of difference channel is to utilize two-way signal generator input phase identical, and two groups of signals that amplitude is different use whether oscilloscope measurement output signal amplitude is that two groups of input signals are only poor, then need the resistance in the circuit to do further correction as if unequal.The effective value change-over circuit also is to utilize signal generator input sinusoidal signal, uses its output voltage of multimeter survey whether to be 1.41 times of input signal amplitude.Through above-mentioned debug process, to guarantee that each electronic circuit of slave hardware can operate as normal.

(4) when the software section of design SCM system, successively liquid crystal data display program, soil resistivity data acquisition program, button setting program, data recording program and wireless data transmission program are debugged several parts and carry out repeatedly debugging and modification.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 constantly debugged compiling, can normally move up to program.

(5) system integration and test.After the completion of four steps, we just must partly combine the hardware and software of total system, carry out system integration and test in the above; Can checking system normally move, and test macro each item performance index are seen the requirement that whether can reach expection; In case of necessity; Also to constantly revise and improve program, can realize to come into operation the function of expecting up to system.The system integration and test of native system is in the laboratory soil sample to be tested; Open the dynamo-electric source of principal and subordinate; Sensor electrode is inserted soil, observe main frame soil resistivity value show whether stable, through button to the data of main frame check, storage and delete function test.Through above-mentioned debug process, system reaches the initial design requirement basically.

The test of system: behind the commissioning test of accomplishing whole system, through 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.Can provide the research of native system through experimental analysis, foundation is provided for further studying than science appraisal.Test through following three parts and to carry out the system testing analysis:

First is the distance and the stability test of wireless data transmission.

Second portion is the stability test in alternating constant-current source.

Third part is soil resistivity and salt content, salt content relation test.

The wireless telecommunications test: the outer open place of wireless telecommunications test locellus and the two kinds of situation in indoor obstacle place are tested, and mainly are the ultimate range that will confirm 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, shows the data that receive if main frame can receive data through 1602, if do not receive then show " abcd ".Table 11, the 12nd, the test case of two kinds of situation of outdoor open area and indoor obstacle place.

Table 11

Table 12

The maximum effective propagation path that can draw at outdoor open area nRF24L01 from table 11 and table 12 is about 95m, is about 75m at the maximum effective propagation path of indoor obstacle place nRF24L01.

The test of alternating constant-current source stability: one of the technological difficulties of utilization " current-voltage " four-end method measured soil resistivity and emphasis are exactly that the alternating constant-current source that is used in the sensor excitation source keeps constant; Stability for the fixed ampllitude alternating constant-current source of detection design; Utilize variable resistor simulated soil impedance variations to make an experiment, be used to test the degree of stability of constant current source.

Method of testing is to increase variable-resistance value gradually; Variation with oscillograph observation signal amplitude; Reach the critical point of sinusoidal signal distortion until driving source two ends output voltage; And write down the resistance value and the magnitude of voltage of some pilot process points and critical point, and calculating the current stability error then, the experimental test data are as shown in table 13.

Table 13

Calculate the relative error that electric current changes,

r＝(I _max-I _min)/I _max·100％ (9)

Get r=2.63%.

Therefore, the amplitude of variation in alternating constant-current source＜3% when load variations, the 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; The mass water content that in indoor soil box, keeps soil is about 15%; The NaCL solution of the variable concentrations of artificial adding equivalent is to increase the salt content of soil; After treating salinity and soil fully mixing, insert the slave sensor electrode, open main frame and receive from machine data.Keeping the sensor electrode insertion depth is 5cm, and measurement data is as shown in table 14.

Table 14

According to the test data in the table 14 is horizontal ordinate with the salt content, and it is as shown in Figure 9 that soil resistivity is that ordinate is made the data scatter diagram.As can be seen from the figure, have good linear relationship between soil resistivity that system records and the salt content, salt content is high more, and the soil resistivity value that records is more little.

The test of soil resistivity and water cut: indoor maintenance soil salt content constantly adds water to improve the water cut of soil in soil about 0.15%, treat that water and soil earth fully mixes after, insert sensor electrode and measure soil sample, open slave and receive from machine data.Keeping the sensor electrode insertion depth is 5cm, and measurement data is as shown in Tble 15.

Table 15

According to the test data in the table 14 is horizontal ordinate with the water cut, and it is shown in figure 10 that soil resistivity is that ordinate is made the data scatter diagram.As can be seen from the figure, have good linear relationship between soil resistivity that system records and the water cut, water cut is high more, and the soil resistivity value that records is more little.

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, effective value change-over circuit, signal amplification circuit, the digital regulation resistance of band 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 on the alternating constant-current source circuit as the driving source of metering circuit, be connected on two current terminals of sensor electrode, after sensor electrode connects driving source; Two voltage ends of electrode will produce voltage difference; Obtain this difference by difference channel,, do the AD conversion by passing to Chip Microcomputer A conversion mouth after the amplifying circuit amplification at the effective value direct current signal that obtains this difference through the effective value change-over circuit.Through wireless module the AD transformation result is sent to main frame at last.

2. wireless multipoint soil resistivity measuring system according to claim 1 is characterized in that the single-chip microcomputer of said host machine part is the STC89C52 single-chip microcomputer, and there is three 16 programmable Timer its inside.

3. wireless multipoint soil resistivity measuring system according to claim 1 is characterized in that, the singlechip that said slave adopts has 8 tunnel 10 AD.

4. wireless multipoint soil resistivity measuring system according to claim 1; It is characterized in that the liquid crystal display of said host machine part liquid crystal display circuit is a HJ1602A graphical dots formation Liquid Crystal Module, is with backlight; Liquid Crystal Module is connected 11 I/O mouths that need take single-chip microcomputer with single-chip microcomputer; The P3.5 of single-chip microcomputer, P3.6, P3.7 mouth link to each other with RS, RW, the E of Liquid Crystal Module respectively, and the P2 mouth links to each other with RS, RW, the E of Liquid Crystal Module, and the P2 mouth links to each other with the data port of Liquid Crystal Module.

5. wireless multipoint soil resistivity measuring system according to claim 1 is characterized in that, said host machine part external data storage circuit AT24C08 adopts the bus and the microcontroller communication of two-wire serial; Voltage is minimum can to arrive 2.5V, and rated current is 1mA, quiescent current 10uA; Voltage 5.5V is a 8K bit serial CMOS E2PROM, and 1024 octets are contained in inside; AT24C08 has one 16 byte page buffer, and this device is operated through the I2C EBI, and AT24C08 is by the P0.6 mouth and the control of P0.7 mouth of single-chip microcomputer; R1, R2 are pull-up resistors; The data line of AT24C08 and address wire are multiplexing, adopt the mode of serial ports to transmit data, only with 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 the said 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 output, channel selection and agreement setting are provided with through the spi bus interface; The design of the power supply of nRF24L01 wireless transmit receiver module with being connected of single-chip microcomputer; Use the AMS1117 stabilivolt to carry out voltage stabilizing,, use the P0 mouth of single-chip microcomputer to be connected with nRF24L01 wireless transmit receiver module to obtain the 3.3V burning voltage.

7. wireless multipoint soil resistivity measuring system according to claim 1; It is characterized in that; Said 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 said slave alternating constant-current source circuit adopts; Output terminal Rsb end can ground connection, and the exchange current source circuit has three parts to constitute, and is respectively reference source, comparison and output.The reference source Vsin of alternating current source circuit is a sinusoidal signal, and 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, said 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; Said slave effective value change-over circuit mainly is made up of real effective conversion chip AD637; Inside comprise active rectifier, square/divider, filter amplifier, impact damper, biasing circuit, dB OUT is the level voltage output terminal, BUFF IN, BUFF OUT are respectively input, the output terminal of impact damper.

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