CN-0164 [ADI]

Low Power, Long Range, ISM Wireless Measuring Node; 低功耗，长距离ISM无线测量节点


型号：	CN-0164
厂家：	ADI
描述：	Low Power, Long Range, ISM Wireless Measuring Node 低功耗，长距离ISM无线测量节点 ISM频段无线
文件：	总5页 (文件大小：122K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

Circuit Note

CN-0164

Devices Connected/Referenced

ADF7020

ISM Band, FSK/ASK Transceiver

Circuit Designs Using Analog Devices Products

Apply these product pairings quickly and with confidence.

For more information and/or support call 1-800-AnalogD

(1-800-262-5643) or visit www.analog.com/circuit.

Low Power, ARM7TDMI, Precision Analog

Microcontroller

ADuC7060

150 mA, Low Quiescent Current, CMOS

Linear Regulator

ADP121

Low Power, Long Range, ISM Wireless Measuring Node

CIRCUIT FUNCTION AND BENEFITS

The system consists of a low power temperature measurement

node that wakes once a minute, measures temperature, transmits

this measurement at 10 kbps to the base node, and then returns

to sleep. The base node continuously listens for a package from

the measurement node and sends this information to the PC via

the UART for display in HyperTerminal.

Ideally, a wireless measurement node is low power, has good

range, and is easily interfaced to different sensors. Through the

combination of three Analog Devices, Inc., parts, an intelligent

measurement node with an average current consumption of

<70 µA, a range of almost 1 km (in free space), and a data rate

of one transmission/minute can be achieved, while also main-

taining a 16-bit ADC performance (see Figure 1). This makes

the circuit suitable for battery power and such applications as

automation and remote sensing.

= 2.5V

ADP121

55µA IN DEEP SLEEP MODE

ID = 1µA WHEN CE = 0V

P0.0

ADuC7060

ADF7020

SCLK

P0.2

P0.4

P1.2

P1.3

PROGRAMMABLE

CURRENT SOURCE

SDATA

SERIAL CONFIGURATION

BUS

SLE

SREAD

100Ω

PT RTD

ADC

PGA

4.7kΩ

OUTGOING DATA

INCOMING DATA

100Ω

0.1%

P0.6

BAT54C

DATA I/O

INT/LOCK

DATA CLK

P0.5

P2.0

P2.1

SERIAL DATA BUS

Figure 1. Low Power, Long Range, ISM Wireless Measurement Node (Simplified Schematic: All Connections and Decoupling Not Shown)

Rev. A

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CN-0164

Circuit Note

The ADuC7060 precision analog microcontroller has a low

power ARM7 core as well as a myriad of precision analog

functions. The onboard multiplexer, digitally programmable

gain amplifier (PGA), voltage reference, programmable current

sources, and 24-bit sigma-delta ADC allow almost any temper-

ature and bridge sensors to be directly connected. In this case, a

4-wire Pt100 (100 Ω platinum RTD) temperature sensor was

chosen. Further details on the measuring circuit can be found

in the AN-0970 Application Note.

The first factor is addressed by choosing low power components

such as the ADuC7060 and the ADF7020. The second factor,

minimizing the activity of the system, is achieved by keeping

the system inactive as long as possible. It is worth considering

the tradeoff between integer versus floating point arithmetic—

in many cases, integer is sufficient, has a shorter execution time,

and, thus, provides greater savings. The final factor, reducing air

time, is achieved in part by using a protocol with minimum

overhead, but also to a large extent by using the ADF7020,

which has very high receiver sensitivity and good out-of-band

rejection, thus maximizing the probability that the data package

contains correct data.

The wireless band chosen for this application is the sub-GHz,

license-free ISM (industrial, scientific, medical) band. The

ADF7020 transceiver, which supports bands in the 431 MHz to

478 MHz as well as the 862 MHz to 956 MHz frequency ranges,

is, therefore, a natural choice. This low power transceiver

requires very few external components, is easily connected to

the ADuC7060 precision analog microcontroller, and offers

excellent performance.

Code Description—General

The system spends the majority of time in deep sleep mode,

with a current consumption of 50 µA to 60 µA (depending on

ambient temperature). Timer 2 wakes the system every second.

Every 60 seconds, an ADC measurement is executed, linearized,

and transmitted. Timer 2 can wake the system from deep sleep;

the other three timers cannot. Timer 2 is 16-bit, meaning that it

wakes every second when running from a 32 kHz clock (in sleep

mode). After the ADC is started, the system goes into pause

mode (see the ADuC7060 data sheet for more information). This

is a reduced power mode, albeit not as reduced as deep sleep.

The ADC wakes the system when finished. A temperature value

is calculated from the ADC results and is packaged and

transmitted.

The ADP121 voltage regulator provides the 2.5 V supply from

two 1.5 V batteries. The very low quiescent current of this

voltage regulator (11µA at no load) is paramount in maxi-

mizing battery lifetime.

CIRCUIT DESCRIPTION

Two buses connect the ADF7020 ISM transceiver with the

ADuC7060 precision microcontroller. Both buses are serial and

bidirectional. One of these buses configures the transceiver, and

it requires four microprocessor ports. The second bus is the

data bus, which enables the data transaction between controller

and transceiver. This bus requires at least three microprocessor

ports. In this particular application, two ports are used instead

of one bidirectional port with two interrupts. This simplifies the

software but necessitates the use of an extra diode and resistor

to separate incoming and outgoing data streams. A parallel

combination of two Schottky diodes ensures a logic low, which

is less than 200 mV. The BAT54C has two diodes in the same

package (connecting Pin 1 and Pin 2 together for a parallel

configuration). All digital ports on the ADuC7060 have

programmable pull-up resistors; however, an external pull-up

resistor is also required. With a data rate of 10 kbps, a 4.7 kΩ

resistor works well.

Packaging essentially means placing appropriate data in a

buffer. In this case, the data consists of a 4-byte floating point

temperature value and a 2-byte CRC (cyclic redundancy check).

In a more complex system, a header with node address, received

signal strength, and other information precedes this data.

Before sending this buffer to the ADF7020 transceiver, an

8-byte preamb to help synchronize the receiving node and a

3-byte synchronization word, or sync word, are sent. This is a

unique 3-byte number that is checked for a match at the receiver

node before a package can be received.

The hardware is very similar on the receiving side; an ADF7020

transceiver is configured to listen for the unique sync word.

After the sync word is received, the data package follows. The

data is sent to the PC via the UART.

Three factors determine the overall current drawn by the

circuit: the requirement of the individual components in both

sleep and active modes), the amount of time the system is

active, and the amount of time the transceiver itself is active.

Flowcharts for the main loops of both the measurement node

and the base receiving node are displayed in Figure 2.

Source code for this circuit can be found at this address:

www.analog.com/CN0164_Source_Code.

Rev. A | Page 2 of 5

Circuit Note

CN-0164

START

1MIN?

START

50µA

INTERRUPT

FROM

ADF7020?

START ADC

200µA

READ ADF7020

DATA

ADC

FINISHED?

AIR DATA LINK

PACKAGE

RECEIVED?

READ ADC

LINEARIZE

25mA

PUT DATA IN SERIAL

BUFFER

TRANSMIT

VALUE

SEND DATA

TO PC

MEASURING NODE

MAIN LOOP

RECEIVING NODE

MAIN LOOP

Figure 2. Measuring and Receiving Node Main Loop Flowcharts

Code Description—ADF7020 Driver

There are many modulation schemes supported by the

ADF7020. In this case, the GFSK (gaussian frequency shift

keying) is used. This has the benefit of having very good

spectral efficiency. In this mode, the ADF7020 generates the

data clock both when transmitting and receiving. The rising

edge of this clock (DATA CLK) generates an interrupt, which

causes the ADuC7060 to place the data on the output port, bit-

by-bit as shown in Figure 3. When all the data has been

clocked-out, the chip select is deasserted, and the ADuC7060

reenters deep sleep mode.

This informs the ADuC7060 processor to prepare for the

reception of a package. Each bit that is received from the

package causes an interrupt in the ADuC7060. In the interrupt

service routine (ISR), the bit stream is read and stored in a

buffer. When all the bytes in the package have been received, a

flag is set to indicate that a new package has been received. The

main loop can now ensure the validity of the package by the

checksum. A correct and complete package can be processed. In

this case, this information is sent via the UART to the PC for

display. The same ISR handles both the sending and receiving of

data to/from the ADF7020 transceiver, as shown in Figure 4.

On the receiving side, the ADF7020 generates an interrupt

when a matching sync word is received (Port INT/LOCK goes

high for nine clock cycles)

Source code for this circuit can be found at this address:

www.analog.com/CN0164_Source_Code.

Rev. A | Page 3 of 5

CN-0164

Circuit Note

INTERRUPT FROM ADF7020 TO ADuC7060 IRQ2

INT/LOCK

9 CLOCK CYCLES

PACKAGE RECEIVED

INTERRUPTS FROM ADF7020 TO ADuC7060 IRQ3

DATA CLK

DATA I/O

DATA PACKAGE (4 BYTES)

CRC (2 BYTES)

Figure 3. Data I/O Timing

ADF7020 INTERRUPT

Rx or Tx?

BIT_CNTR < 7

YES

BIT_CNTR < 7

YES

BIT_CNTR = 0

STORE BYTE

CLOCK-OUT BIT

TO ADF7020

INC. BIT_CNTR

END OF

PACKAGE?

CLOCK-IN BIT

FROM ADF7020

ALL BYTES

SENT?

SET PACKAGE

Rx FLAG

YES

INC. BIT_CNTR

DISABLE INTERRUPT

EXIT INTERRUPT

Figure 4. Interrupt Service Routines for Handling Rx and Tx Data

Rev. A | Page 4 of 5

Circuit Note

CN-0164

Data Sheets and Evaluation Boards

ADF7020 Data Sheet

COMMON VARIATIONS

Depending on the desired frequency, there are a number of

other products that can be used instead of the ADF7020. For

example, for the 2.4 GHz frequency band, the ADF7242 is a

very good choice.

ADF7020 Evaluation Board

ADF7020 Device Drivers

ADuC7060 Data Sheet

ADuC7060 Evaluation System

ADP121 Data Sheet

LEARN MORE

Source code for CN-0164

Looney, Mike. AN-0970 Application Note. RTD Interfacing and

Linearization Using an ADuC706x Microcontroller, Analog

Devices.

REVISION HISTORY

2/11—Rev. 0 to Rev. A

Change to Circuit Function and Benefits ......................................1

10/10—Revision 0: Initial Version

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CN09100-0-2/11(A)

Rev. A | Page 5 of 5

CN-0164 [ADI]

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