利用智慧射频晶片nRF9E5实现温度、湿度无线测量电路设 计
Designof wireless measurement circuit for temperature and humidity by usingintelligent RF chip nRF9E5
Internetaccess time: 01 October 2004
Theprint edition recommends sending inquiries to colleagues
NRF9E5is a smart RF chip with a working frequency of 433/868/915MHz. Itintegrates 8051 micro controllers, 4 channels, 10 bit A/D conversion,and multi-channel RF transceiver. This paper introduces the RF chipLM71, temperature sensor, humidity
sensing circuit design method and program realization of wireless temperature and humidity measuring sensor HS1101, which is simple and reliable and flexible and
|
-100dBmreceiving sensitivity, time is only 2.5 ~ A in the current low power,especially suitable for battery powered, wireless keyboard, wirelesstelephone, industrial wireless headset, wireless sensor, remotecontrol and wireless alarm etc..
Thispaper introduces a method of wireless temperature and humiditywireless induction measurement circuit using nRF9E5, 14 bit digitaltemperature sensor LM71 and humidity sensor HS1101. Compared withwire induction measurement, wireless induction measurement has theadvantages of high reliability, easy installation, simple
structure, repeated use and |
|
convenientsystem maintenance. This design makes full use of the low powerconsumption characteristics of each component, and uses 3.6V lithiumbattery in the wireless temperature and humidity sensor. It can notonly prolong the service life of the battery, but also make thewireless data transmission more convenient and flexible.
NRF9E5function introduction
Figure1 shows the internal block diagram of the nRF9E5. NRF9E5 is anembedded nRF905 wireless transceiver chip integration, enhanced 8051microcontroller and 4 Channel 10 bit ADC, the sampling rate is80ksps, including 1.22V voltage reference, power management, PWMoutput, UART non synchronous serial port and SPI
communicationinterface, interface logic circuit, watchdog circuit, multi-channel
frequency inductor and filter has been built, the surrounding elements rarely, consistent
|
protocoleliminates the built-in software programming error correctionsoftware developers and micro controller error correcting operation,reducing the difficulty of developing wireless applications.
Figure1 below shows the external memory of EEPROM 25320 for nRF9E5 (Figure2, U2) and the capacity of 4K bytes (4096 * 8b) for applicationsstored on nRF9E5.
Whenpowered on, nRF9E5
importsthe application into the on-chip RAM via its SPI interface throughits internallysolidified loader (Boot).
Designof wireless temperature and humidity inductance measuring circuit
Awireless temperature and humidity sensor is constructed by using RFchip nRF9E5, 14 bit digital temperature sensor LM71 and humiditysensor HS1101.
LM71is a low power, Delta - Sigma ADC temperature sensor with 14 bits(including 1 symbol bits) produced by National Semi-conductorCorporation,
Thetemperature range of -40 DEG ~150 DEG, 0.03125 DEG C temperature
resolution,measurement precision in the -40 range of ~150 DEG C - 1.5 DEG C, thepower supply voltage is 2.65V~5.5V, with three line serial interfaceSPI/MICROWIRE compatible interface, easy and microprocessor.Therefore, in Figure 2 U3 (LM71) SC serial clock, serial input andoutput of SI/O, CS and U1 respectively, chip select
(nRF9E5)P02, P01 and P00 connected to the RF circuit LM71, nRF9E5 and singleended
ambient temperature and LM71 temperature sensors is shown in table 1.
|
capacitorwith the air humidity
increases,the relative humidity in the range of 0%-100%RH, the capacity of thecapacitor varies from 160pF to 200pF, the error is less than 2%RH,the response time is less than 5S, temperature coefficient 0.04pF/ C.
Asshown in Figure 3, the humidity sensitive capacitor at the 555 Cxoscillator circuit, switching capacitor will change into voltagesignal and the frequency is inversely proportional to the frequencyof the signal, the microcontroller can directly be collected.
The high level time of the two square wave signals (3 pin output of U4 in Fig. 3) of the | |
oscillation circuit of the transient state output frequency is |
|
Outputlow time is
Therefore,the period of the output square wave signal is
Thatis
EEPROMprogramming
Themain program nRF9E5 stored in the serial EEPROM outside, when thewafer starts up, the internal curing manufacturers to lead theprogram through the SPI interface, the external EEPROM in the mainprogram into nRF9E5 RAM (4K byte space is not occupied by the mainprogram can be used as the on-chip RAM), then execute the jumpinstruction, start the main program execution. The main program needsto be written to EEPROM in accordance with the rules shown in Table2, where SPEED (bit3) is the
(bit2,1,0) is the frequency of an external 011=16MHz, 100=20MHz. |
registers,so you can use MCS51 series simulation software for programming, andfinally put the program into the EEPROM debugging.
Byusing WAVE6000 simulation software (Wei Fu) preparation of wirelessradio frequency communication and data acquisition and dataconversion program, compiled into HEX suffix for the data file"XXXXXXXX.HEX", the a text format: each line of firstcharacters ", said:" the fixed line started; second, thirdcharacters for instruction data bank the number of M (16 m), M 20H,said the M double byte data, 2M characters, fourth,fifth, sixth, 7 characters for the row address, eighth, ninthcharacters for "00" or "01" for the rest of 2Minstruction data characters arranged in sequence,
Thelast 2 bits are to verify the character. The end of the HEX ':00000001FF'.
Usingadvanced programming language Delphi 6 in the Windows2000 environmentto open the data file, sequentially reading each row of data, removethe first 9 characters of each line and each line of the last twocharacters, the other is the user's main program file, the programwill head the main program files before adding in Table 2, formnRF9E5 external EEPROM format program. As shown in Figure 4, it canbe written to EEPROM chip 25320 through RS232 communication andAT89C2052.
Author:Zhu Zhaoqing
NantongInstitute of Technology
Email:zhu.