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ATLAS-Q100L-SMARTPALLET

Application note

EPC C1G2 COMPLIANT BATTERYLESS SMARTPALLET WITH WIRELESS UNIQUEIDENTIFIER AND INTEGRATED SCALE

AN-ATLAS-Q100L-SMARTPALLET-V01

• 860MHz-960MHz operation

• EPC Class-1 G2 compliant

• ISO 18000-6 Type C compliant

• 96-bit EPC & 32-bit TID

• Weight measurement from 0kg up to 150kg

• Weight resolution: 150g

• Weight accuracy: ±1kg

DESCRIPTION

SmartPallet is an example application for the ATLAS-Q100L battery free wireless sensor tag from Farsens. Thistag provides a standard pallet with passive UHF RFID identification. Moreover, it provides the pallet with theability to measure the weight it is supporting. Both, the identification and weight measurement, are done batteryfree with the energy received from a standard UHF RFID reader.

These RFID sensor tags are compatible with commercial UHF RFID readers (EPC C1G2). With a 2W ERP setupthe battery-less weight scale can communicate to over one meter and a half - 5 feet.

BLOCK DIAGRAM

The SmartPallet device consists of an ATLAS-Q100L batteryless quad compression load meter tag attached toa standard EUR-6-pallet (half the size of the EUR-pallet). For a more detailed description of the ATLAS-Q100Lrefer to its product brief.

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ATLAS-Q100L-SMARTPALLET

Application note - AN-ATLAS-Q100L-SMARTPALLET-V01 - NOVEMBER 2014 WWW.FARSENS.COM

ATLAS-Q100L

RF+

RF-

FX1901S1+

S1-

VN1

S2+

S2-

VN2

VP2

S3+

S3-

VN3

VP3

S4+

S4-

VN4

VP4

VP1

FX1901

FX1901

FX1901

Power Harvesting

Communication

Power Management

Signal Conditioning

EUR-6-pallet

In order to attach the FX1901 compression load cell to the pallet, 4 mechanical adapters have been used.These adapters have been designed specifically to insert the compression load cells inside them and screwthe adapters to the pallet. This way, the vertical force of the weight of the pallet is transmitted directly to theFX1901 transducers.

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ATLAS-Q100L-SMARTPALLET

Application note - AN-ATLAS-Q100L-SMARTPALLET-V01 - NOVEMBER 2014

CHARACTERISTICS

SYMBOL PARAMETER MIN TYP MAX UNIT

RFID

RFSENS RF sensitivity fully passive -4 -2 0 dBm

OPERATING CONDITIONS OF TAG

TOP Operating temperature range -30 85 ◦C

WEIGHT MEASUREMENT

Wrange Weight range 0 150 kg

Wacc Weight accuracy ± 1 ± 2 kg

Wres Weight resolution 150 g

The following graph shows the precision of the weight measurement depending on the weight placed over thepallet:

Figure 1: Measurement accuracy vs weight value

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OPERATION

EPC reading

In order to read the EPC of the TAG, commercial EPC C1G2 readers can be used. However, some considerationshave to be taken into account.

As the tag has a large supply capacitor connected to VDD, the power-up of the system will be slow. It canlast several seconds. In order to speed up the charge process, the reader shall be configured to send poweras continuously as possible. Refer to the application note External capacitor on VDD of ANDY100 for detailedinstructions on how to set up the reader for best performance.

Once the supply capacitor is charged, the TAG will respond with its EPC. From this point on, memory accesscommands can be used to control the contact temperature sensor via the SPI bridge.

Weight reading

The output voltages of the sensors connected to the VMETER-LV10 can be read using standard EPC readcommands. It is important to take into account that the values returned to such a request contains the readingsof the previous measurement. As the measurement process takes longer than the communication, upon receivinga voltage reading request the tag answers with the value of the previous measurements and triggers a new one.In order to get an up to date measurement, it is mandatory to perform at least two readings.

Read Weight Operation: ReadMemory bank: User MemoryWord Pointer: 0x03Word Count: 6

The answer from the tag to such a request will contain 12 bytes of data. The EPC word size is 16bits and theSPI word size is 8bits. The answer received from the SPI interface is right aligned in the EPC words. Assumingthat the reader returns the received data in the buffer of bytes rawdata, the content of the answer is defined asfollows:

Byte 0

0x00 FW_VER 0x00 CH1[9:2] 0x00CH1[1:0]CH2[9:4]

0x00CH2[3:0]CH3[9:6]

Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7rawdata

content 0x00CH3[5:0]CH4[9:8]

Byte 8 Byte 9

0x00 CH4[7:0]

Byte 10 Byte 11

• FW_VER: firmware version included in the micro-controller.

• CH1[9:0]: channel 1, 10 length ADC reading.

• CH2[9:0]: channel 2, 10 length ADC reading.

• CH3[9:0]: channel 3, 10 length ADC reading.

• CH4[9:0]: channel 4, 10 length ADC reading.

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The conversion from the ADC readings to the actual weight values has to be done by software in the readerside. In order to make the conversion, the calibration constants K 1 and K 2 have to be known. The conversion toweight value can be done as shown in the following sample code:

UInt16 ADCvalCH1, ADCvalCH2, ADCvalCH3, ADCvalCH4;

float W;

// Get ADC measurement

ADCvalCH1 = (UInt16)((rawdata[3] << 2) | rawdata[5] >> 6) & 0x3FF;

ADCvalCH2 = (UInt16)((rawdata[5] << 4) | rawdata[7] >> 4) & 0x3FF;

ADCvalCH3 = (UInt16)((rawdata[7] << 6) | rawdata[9] >> 2) & 0x3FF;

ADCvalCH4 = (UInt16)((rawdata[9] << 8) | rawdata[11]) & 0x3FF;

// Calculate measured Weight

W = K1 + K2*(ADCvalCH1+ADCvalCH2+ADCvalCH3+ADCvalCH4);

Calibration parameters reading

Instead of using the default calibration parameters of the ATLAS-Q100L, the SmartPallet has been calibrated inweight. As the reading of each compression load cell reflects the weight supported by the individual cell, the sumof the four cells is used to get the total weight of the SmartPallet. The calibration is done in two points (20kgand 80kg), so that two calibration parameters are obtained. These calibration parameters are stored in NVM.Each parameter consists of a 32 bit floating point value. These parameters can be read through the EPC C1G2interface reading the following addresses of the user bank:

Read K1 Operation: ReadMemory bank: User MemoryWord Pointer: 0x04Word Count: 5

The content of the answer to such query is defined as follows:

Byte 0

0x00 FW_VER 0x00 K1_XL 0x00 K1_L 0x00 K1_M

Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7rawdata

content 0x00 K1_S

Byte 8 Byte 9

• FW_VER: firmware version included in the micro-controller.

• K1 (XL:L:M:S): calibration word 1 (float32).

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Read K2 Operation: ReadMemory bank: User MemoryWord Pointer: 0x08Word Count: 5

The content of the answer to such query is defined as follows:

Byte 0

0x00 FW_VER 0x00 K2_XL 0x00 K2_L 0x00 K2_M

Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 Byte 6 Byte 7rawdata

content 0x00 K2_S

Byte 8 Byte 9

• FW_VER: firmware version included in the micro-controller.

• K2 (XL:L:M:S): calibration word 2 (float32).

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ATLAS-Q100L-SMARTPALLET

Application note - AN-ATLAS-Q100L-SMARTPALLET-V01 - NOVEMBER 2014

DEMO SOFTWAREDemonstration software to read weight value of the SmartPallet is available in the web www.farsens.com. Thesoftware is compatible with commercial UHF RFID readers such as:

• Impinj R420

• Sirit IN610

• Alien ALR9900

• Mercury M6

• Motorola FX9500

• Motorola FX7400

• Nordic Stix

• Nordic Sampo

• Nordic Morphic

• Nordic Merlin

For the complete supported reader list check the website. Download the latest software and user guide at:http://www.farsens.com/software.php

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