CN102998653A - Wireless monitoring position finder - Google Patents

Abstract

A wireless monitoring position finder is used for locating an old person (or patient) when seeking the same. The wireless monitoring position finder comprises a radio frequency node carried by the old person (or patient) and a position finder carried by a guardian. The radio frequency node comprises a single chip microcomputer, a wireless transceiving module and an antenna. The position finder comprises a single chip microcomputer, a wireless transceiving module, an antenna, a liquid crystal display and a display driver. The position finder can position the old person (or patient) in a distance not larger than 100m from the guardian and displays relative position between the old person (or patient) and the guardian. The limitation that a GPS (global positioning system) cannot be applied indoor or in places with obstacles is broken through, and cost is low.

Description

Wireless monitoring position indicator

1. technical field

It is positioned when old man (or patient) is found when the distance that wireless monitoring position indicator is used for old man (or patient) and guardian is not more than 100 meters. 

2. background technology

Old man (or patient) can wander away often; most commonly it is temporarily disengaged from the visual line of sight of guardian; GPS location is all used substantially to old man (or patient) at present; cost is higher; positioning precision is relatively low; it can only obtain the longitude and latitude of current location, and indoors or barrier occasion can not be applied. 

3. the content of the invention

Wireless monitoring position indicator includes two parts, and one is the radio-frequency nodes that old man (or patient) carries, and two be to have liquid crystal display on the position indicator that guardian carries, position indicator.(such as Fig. 1 when guardian finds old man (or patient), positioned at A points), press " searching " button on position indicator, position indicator sends radiofrequency signal, radiofrequency signal that position indicator sends can be received if radio-frequency nodes are old man (or patient) within 100 meters of position indicator and the radiofrequency signal of a response is replied, radiofrequency signal of the position indicator by the reply, the transmission power of radio-frequency nodes is known, position indicator measurement while answer signal is received receives the power of signal, signal intensity is converted into by i.e. the distance between radio-frequency nodes and the position indicator R of distance according to radio signal attenuation empirical model, as shown in Figure 1；Position indicator moves a certain distance arrival B points along a certain determination direction and sends radiofrequency signal, radio-frequency nodes receive one answer signal of radiofrequency signal and reply that position indicator is sent, position indicator can be measured and the distance between radio-frequency nodes r, then old man (or patient)) P points or Q points must be located at；Position indicator is moved to C points along the direction vertical with AB, if position indicator measure with the increase of the distance between radio-frequency nodes, old man (or patient) is in Q points, and otherwise old man (or patient) is in P points.Pattern shown in Fig. 1 can be shown on a liquid crystal display. 

4. brief description of the drawings

Fig. 1 is positioning principle schematic diagram

Fig. 2 is position indicator circuit theory diagrams

Fig. 3 is radio-frequency nodes circuit theory diagrams

Fig. 4 is CC2500 wireless transceiver circuits

5. embodiment

Fig. 2 and Fig. 3 are respectively position indicator circuit theory diagrams and radio-frequency nodes circuit theory diagrams, and position indicator and radio-frequency nodes all use MSP430 single-chip microcomputers as master controller, and MSP430 single-chip microcomputers most outstanding feature is exactly super low-power consumption.CC2500 is selected in the transmission of radiofrequency signal, CC2500 is low in energy consumption, communicated using 4 line SPI interfaces with MSP430F149, digital RSSI (received signal strength) is automatically generated after signal is received every time, it is illustrated in figure 4 CC2500 wireless transceiver circuit figure, R4 is resistance device partially, and accurate bias current is worth to according to different settings；Energy supply is made up of in the appropriate decoupling at supply pin, balanced to unbalanced transformer C14, C15, L2 and L3, by CC2500 RF differential port translation into RF single-ended signals.The antenna ANT-821 that wireless receiving and dispatching is used is 2.4GHz ceramic antenna, and size is 8.5mm × 2.0mm, is for this frequency range broadband communication design specialized antenna, with the impact of good vibration proof and anti-aging ability.Liquid crystal display uses single color point type liquid crystal display device, can show word and figure. 

The propagation of radiofrequency signal is easily influenceed by factors such as multipath, non line of sight, and RSSI (received signal strength) value is reduced with the increase of communication distance.After working environment is determined, the correct transmission power for choosing wireless network node, you can set up the Mathematical Modeling of RSSI and distance relation. 

$P\left(d\right)=P\left(d_0\right)-{10n}_p\log \left(\frac{d}{d_0}\right)+X_{\mathrm{\σ}}$

In formula：d₀--- reference distance, m

      n_P--- path attenuation coefficient, taken different value by surrounding environment influence

      X_σ--- with δ²For the normal distribution of variance, for reducing the error of signal intensity

The general principle of RSSI rangings of the present invention is：The transmission power of known node, then the receiving power of receiving node is read, the propagation loss of radio wave is calculated, wireless signal propagation model formula is reused and is translated into distance.After many experiments, the empirical data table that can set up under specific environment or measurement result is modified by the adjustment of attenuation coefficient. 

RSSI (received signal strength) signals are influenceed fluctuation larger by extraneous factor, such as surrounding environment, barrier coefficient, measurement error, antenna gain and transmission power, the situation of weather also causes different degrees of influence to signal attenuation during outdoor measurement, such as thundery sky, snow, mist, morning and evening on the same day, the extraneous factor of influence formed was also different when measuring, the n under varying environment_pAnd X_σValue is as shown in table 1, and position indicator can select n according to specific environment when in use_pAnd X_σValue. 

CC2500 supports different transmission power levels and message transmission rate, is set as that more than 100m communication distance can be reached during peak power, but signal attenuation fluctuation range is big, brings ranging localization poor accuracy；Easily occur blind area in normal communications range from lowest power, therefore the present invention chooses median and is used as transmission power. 

MSP430 and CC2500 is communicated by 4 line SPI compatibility interfaces (SI, SO, SCLK and CSn).The data collected after treatment, the TX FIFO of CC2500 wireless modules are write by spi bus, while radio-frequency module is switched into transmission state by MSP430.The process for transmitting wirelessly data is as follows：CC2500 first forms the data in FIFO stack plus frame head, postamble and check code etc. the packet for meeting data communication protocol form, then carries out broadcasting using O-QPSK modulation system after DSSS.The process that wireless module receives data is as follows：Signal progress O-QPSK is reversely demodulated, then carries out reverse DSSS, obtains being stored in radio-frequency module CC2500 RX FIFO after complete packet, MSP430 is finally notified in the way of interruption. 

CC2500 RF power outputs have the grade of two PLC technologies, and special PATABLE registers can carry out the setting of power output simultaneously for 8 users.The wireless signal strength value for receiving whole frame is stored in specific RSSI registers 0x34 by CC2500, and the register 0x34 values of receiving node are read first, and the empirical equation then propagated according to signal calculates the distance of position indicator and radio-frequency nodes.Signal strength values are represented in general CC2500 in the form of complement code, its unit is dBm, is rule of thumb needed it plus an offset, transmission rate when being 500kbit/s of tabling look-up to obtain, offset is no more than -72, and this numerical value can be determined according to experiment. 

Claims (4)

1. a kind of wireless monitoring position indicator, it is characterised in that：It is made up of radio-frequency nodes and position indicator；The radio-frequency nodes are using single-chip microcomputer as master controller, and antenna is connected by radio receiving transmitting module with single-chip microcomputer；The position indicator is using single-chip microcomputer as master controller, and antenna is connected by radio receiving transmitting module single-chip microcomputer, and liquid crystal display is connected by driver with single-chip microcomputer.

2. wireless monitoring position indicator as claimed in claim 1, it is characterised in that described antenna is ceramic antenna.

3. wireless monitoring position indicator as claimed in claim 1, it is characterised in that described radio receiving transmitting module is connected by SPI interface with single-chip microcomputer.

4. wireless monitoring position indicator as claimed in claim 1, it is characterised in that described liquid crystal display is single color point type liquid crystal display device. 

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