circuit note cn- 0164 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 . devices connected /referenced ADF7020 ism band, fsk/ask transceiver aduc7060 low power, arm7tdmi, precision analog microcontroller adp121 150 ma, low quiescent current, cmos linear regulator low power, long range, ism wireless measuring node rev. a circuits from the lab? circuits from analog devices have been designed and built by analog devices engineers. standard engineering practices have been employed in the design and construction of each circuit, and their function and performance have been tested and verified in a lab environment at room temperatur e. however, you are solely responsible for testing the circuit and determining its suitability and applicability for your use and application. accordingly, in no event shall analog devices be liable for direct, indirect, special, incidenta l, consequential or punitive damages due to any cause whatsoever connected to the use of any circuits from the lab circuits. (continued on last page) one technology way, p.o. box 9106, norwood, ma 02062 - 9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.461.3113 ? 2011 analog devices, inc. all rights reserved. circuit function and benefits 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 cu rrent consumption of <70 a, a range of almost 1 km (in free space) , and a data rate of one transmission /min ute 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. 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 hypert erminal. aduc7060 ADF7020 09100-001 pga adc adp121 3v 100? pt rtd 100? 0.1% 55 a in dee p slee p mode id = 1 a when ce = 0v p0.6 p0.5 p2.0 p2.1 dat a clk int/lock dat a i/o outgoing d at a incoming d at a p0.4 p1.2 p1.3 sread sle sdat a p0.2 sclk p0.0 ce v cc seria l configur a tion bus v cc = 2.5v seria l d at a bus ba t54c 4.7k? programmable current source figure 1. low power, long range, ism wireless measurement node (simplified schematic: all connections and decoupling not shown)
cn- 0164 circuit note rev. a | page 2 of 5 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 ? p latinum rtd) temperature sensor was chose n . further details on the measuring circuit can be found in the an - 0970 application note . the wireless band chosen for this application is the sub - ghz , license - free ism ( i ndustrial, scientific, m edical) band . the ADF7020 transceiver, which supports bands in the 43 1 mhz to 478 mhz as well as the 862 mhz to 956 mhz frequency range s, 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. 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 (11a 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 tran s ceiver, 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 bidi rectional 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 diode s ensures a logic low , which is less than 2 00 mv . the bat54c has two diodes in the same package (connect ing pin 1 and pin 2 together for a parallel configuration) . all digital ports on the aduc7060 have programmable pull - up resistors; however , an exte rnal pull - up resistor is also required. with a data rate of 10 kbps, a 4.7 k ? resistor works well. three factors determine the overall current drawn by the circuit : the requirement of the individual components in both sleep and active mode s ), the amount of time the system is active , and the amount of time the transceiver itself is active. the first factor is addressed by choosing low power components such as the aduc7060 and the ADF7020 . the second factor, minimizing the activity of t he system , is achieved by keeping the system inactive as long as possible. it is worth considering the tradeoff between integer versus float ing 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 . code description general the system spends the majority of time in deep sleep mode, with a current consumption of 50 a to 60 a ( depending on ambient tempe rature). 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 in to pause mode (see the ad uc7060 data sheet for more information ). this is a reduced power mode, albeit not as red uced as deep sleep. the adc wakes the system when finished. a temperature value is calculated from the adc results and is packaged and transmitted. packaging essentially means placing appropriate data in a buffer. in this case , the data consists of a 4 - byt e 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 precede s 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 receive r node before a pac kage can be received. the hardware is very similar on the receiving side ; a n ADF7020 transceiver is configured to listen for the unique syn c word. after the sy nc word is received , the data package follows. th e data is sent to the pc via the uart. flowcharts for the main loops of both the measurement node and the base receiving node are displayed in figure 2 . source code f or this circuit can be found at this address: www.analog.com/cn0164_source_code .
circuit note cn- 0164 rev. a | page 3 of 5 start 09100-002 start adc transmit value 50 a no no no 1min? start n interrupt from ADF7020? p ackage received? 200 a 25m a no adc finished? read adc linearize air d at a link read ADF7020 data send data to pc put data in serial buffer measuring node main loo p receiving node main loo p figure 2. measuring and receiving node main loop flowcharts code description ADF7020 d river there are many modulation schemes supported by th e 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 adf702 0 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 re enters deep sleep mode. on the receiving side, the ADF7020 generates an interrupt when a matching sync word is received (p ort int/lock goes high for nine clock cycles) this informs the aduc7060 processor to prepare for the recept ion 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 t he 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 t he uart to the pc for display . the same isr hand l es both the sending and receiving of data to/from the ADF7020 transceiver , as shown in figure 4 . source code for this circuit can be found at this address: www.analog.com/cn0164_source_code .
cn- 0164 circuit note rev. a | page 4 of 5 09100-003 data i/o data package (4 bytes) 9 clock cycles crc (2 bytes) int/lock data clk interrupt from ADF7020 to aduc7060 irq2 interrupts from ADF7020 to aduc7060 irq3 p ackage received figure 3. data i/o timing 09100-004 ADF7020 interrupt bit_cntr = 0 bit_cntr = 0 rx or tx? end of p ackage? al l bytes sent? bit_cntr < 7 bit_cntr < 7 clock-in bit from ADF7020 store byte clock-out bit to ADF7020 set package rx flag inc. bit_cntr disable interrupt exit interrupt inc. bit_cntr rx tx yes no yes yes figure 4. interrupt service routines for handling rx and tx data
circuit note cn- 0164 rev. a | page 5 of 5 c ommon variations depending on the desired frequency, there are a num ber 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. learn more source c ode for cn - 0164 looney, mike. an - 0970 application note . rtd interfacing and linearization using an aduc706x microcontroller , analog devices. data sheets and evaluation boards adf702 0 data sheet ADF7020 evaluation board a df7020 device drivers aduc706 0 data sheet aduc70 60 evaluation system adp12 1 data sheet revision history 2 /11 rev. 0 to rev. a change to circuit function and benefits ...................................... 1 10 /10 rev ision 0 : initial version (continued from first page) circuits from the lab circ uits are intended only for use with analog devices products and are the intellectual property of analog devices or its licensors. while you may use the circuits from the lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectual property by application or use of the circuits from the lab circuits . information furnished by analog devices is believed to be a ccurate and reliable. however, circuits from the lab circuits are supplie d "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warrant y of merchantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by analog devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. analog devic es reserves the right to change any circuits from the lab circuits at any time without notice but is under no obligation to do so. ? 2011 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. cn09100 - 0 - 2/11(a)
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