DIGITAL COMPASS + ALTIMETER MODULE

Transcription

1 EPT2001-O DIGITAL COMPASS + ALTIMETER MODULE DESCRIPTION The EPT2001-O consists of 2 PNI s magneto-inductive sensors and its driver to get compass heading data and an INTERSEMA calibrated pressure sensor to get atmospheric pressure. The altitude level referenced to sea level can therefore be approximated accordingly. The weather based on the change in the rate of the pressure over a period can be predicted. A microprocessor controls the measurement sequence of the sensors, and all the parameters that use to compensate for magnetic disturbance are collected during compass calibration. FEATURES o Supply voltage 2.5 V to 3.3 V o Low supply current o 10 o C ~ +60 o C o Digital Compass Range: 0 o ~359 o Accuracy: +/- 5 o Resolution: 1 o o Pressure Range: 300~1100mbar Accuracy: +/- 1.5mbar Resolution: 1mbar o Altitude Range: -700m~8950m Accuracy +/- 20m Resolution: 1m o Temperature Range: -10 o C~+60 o C Accuracy +/- 1 o C Resolution: 0.1 o C o Weather Forecast Sunny Slightly Cloudy Cloudy Rainy o rev 4.5 Page 1 of 13

2 BLOCK DIAGRAM M agnetometers 2-Axis Vdd=3.0V PNI11096 Driver ELO Micro Processor ELI SCLK DIN DOUT SEL MS5534M Gnd Fig 1. Electrical Block Diagram COMPASS MEASUREMENT In operation, the microprocessor takes a pairs of measurements that are combined to calculate the heading data. Raw data is processed at 8Hz to handle gain matching, offset zeroing, phase shifting, and hard iron compensation for the magnetic measurements. To make a measurement, the sensor is switched to into a LR oscillator circuit. The selected sensor oscillates at a frequency, which relates to the magnetic field sensed by the sensor. The frequency counts for a certain number of time periods are used to calculate the magnetic field strength measured by each sensor. COMPASS CALIBRATION All digital compasses have to be calibrated in order to compensate for magnetic fields other than the earth s field component to get accurate heading. These additional magnetic fields are generated by the host and therefore depend on the compass mounting location. By performing a simple procedure the module can compensate for steady, static magnetic fields know as hard iron fields. The phase shift due to sensor mounting and axis mismatched can be self-corrected. The backlight offsets (if any) imposed to the field can also be approximated and therefore eliminated. Field components found after a calibration are only valid for a particular orientation and location of the compass. A re-calibration is necessary after a relocation of the compass or if the platform has changed its magnetic character. During calibration procedure the compass collects data required for the compensation algorithm. The goal of the calibration is to sample the magnetic field components for many possible orientations of the host. Rotating the host through 360 degrees or driving in a circle will enable the compass to sample its magnetic environment rev 4.5 Page 2 of 13

3 PRESSURE AND TEMPERATURE MEASUREMENT The MS5534A consists of a piezoresistive sensor and a sensor interface IC. It is to convert the uncompensated analog output voltage into a 16 bit digital value, as well as providing a 16 bit digital value for the temperature. For the pressure measurement, the differential output voltage from the pressure sensor is converted; for the temperature measurement, the sensor bridge resistor is sensed and converted. The 16 bit values for pressure and temperature are read via the serial interface. Then the real pressure and temperature are calculated out of data and calibration coefficients. PRESSURE ALTITUDE CONVERSION Pressure to altitude conversion is based on 1976 US Standard Atmosphere Assumptions. For simplicity, the altitude conversion applies piece-wise linear interpolation with reduced accuracy but with an acceptable number of operations computation time. altitude A(pri) [m] vs pressure [10mbar; kpa] Pri Pi rev 4.5 Page 3 of 13

4 Altitude error di [m] vs pressure P [kpa=10mbar] di Pi WEATHER FORCAST The weather condition is calculated from absolute pressure once when power up. Absolute Pressure / mbar Weather Condition Weather Code P < 970 Rainy < P <1000 Cloudy < P < 1030 Slightly Cloudy 3 P >1030 Sunny 0 The weather forecast is calculated from the change in pressure per time period. The change in weather condition is directly proportional to the speed of change in barometric pressure. Rising slope indicates High Pressure System and good weather trend. Falling slope means Low Pressure System and bad weather trend. Fluctuating pressure maybe due to sudden change of condition is filtered out and no weather forecast will be made. It will restart to monitor the pressure lotus for preset time period. Barometric pressure keeps constantly rising or falling during past time period, say 1 hour, will effectively change weather condition. (Weather Change is in equal to Pressure Derivative in mbar) It takes barometric pressure every 20mins and compares current pressure with the reference to trace the changing. If the pressure keeps rising or falling more than 1 hour, weather condition will be changed relatively to the change in pressure rev 4.5 Page 4 of 13

5 PIN CONFIGARATION Name In/Out Pin Description VDD I 1 Voltage supply 3.0V ELI * I 2 Back light control in (active high) DOUT O 3 Data transmit out DIN I 4 Data receive in SEL I 5 Chip enable & select in SCLK I 6 Serial data clock out GND I 7 Power and signal ground ELO * O 8 Back light on/off * Note: The module can get reliable heading even when the backlight turns on provided that the calibration is performed correctly. Please refer to the programming flow for the procedure. SERIAL COMMUNICATION The module communicates with microprocessor via a 4-wire serial interface as shown in Figure 1. The serial clock (SCLK) initiates the data transfer and synchronizes the data transfer with each bit being transmitted on the falling edge of SCLK and each bit being received on the rising edge of SCLK. This signal is generated by master device. The data out (DOUT) indicates the data transmission status and the conversion results. The output data at the data in (DIN) depend on the received command bits. Every communication starts with an instruction sequence at pin DIN. Figure 2 shows the timing diagram. The SEL signal (>50ms) sets the internal logic control into the initial state. It is a must to reset it before the start of the communication. There is a start sequence (3 bits high) and ends with a stop sequence (3 bits low) for each data reading. The start sequence followed by 6 command bits that selects different measurement or calibration. The module acknowledges the completion of conversion by a high to low transition at pin DOUT and data are ready to be read out triggered by data clock (SCLK). SEL >50ms SCLK 13th extra clock // DOUT // acknowledge // bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 bit7 // bit0 DIN bit0 bit1 bit2 bit3 bit4 bit5 bit6 bit7 bit8 bit9 bit10 bit11 Fig 2. Communication Timing Diagram rev 4.5 Page 5 of 13

6 The command bits (Least Significant Bit first) select and start conversion for corresponding mode and return decimal digits in a series way (Most Significant Bit first) as follows: Mode Command Bits (Bin) Command Bits (Hex) Heading Measurement B 16H Calibration (Start/Stop) B 32H Pressure and Weather B 2AH Temperature B 26H Altitude B 1AH Serial Data Format B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 CHKSUM DATA 1000 DATA 100 DATA 10 DATA1 Check Sum: (4 bits) The hex addition without carry value of the 16 bits data Data: (16 Bits) o Calibration Start/Stop ACK DATA 0A0A if received START/STOP command o Compass Heading 12 Bit heading (0 o ~359 o ) and signal disturbed bits (1010B) Case 1: Case 2: FA005 Heading=135 o (magnetic field normal) Checksum=7 Heading=5 o (magnetic field disturbed) Checksum=0F o Pressure and weather 14 Bit pressure (300mbar~1100mbar) and 2 Bit weather code (bit15, bit14) Case 1: 0D003 Pressure=1003mbar; weather code=11 (slightly cloudy) Checksum= D=0 Case 2: B0999 Pressure=999mbar; weather code=00 (sunny) Checksum= =B rev 4.5 Page 6 of 13

7 o Altitude 16 Bit altitude data (-700m~8950m) in 2 s complement If MSN (most significant nibble) = 9, it is negative. Case 1: MSB=2, Altitude= +2300m Checksum=5 Case 2: MSB=9, Altitude= = -450m Checksum=3 o Temperature 16 Bit temperature data (-10 o C~60 o C) in 2 s complement Case 1: Case 2: Temperature=+25.0 o C Checksum=7 Temperature= o C Checksum=0 ( =10.0) PROGRAMMING FLOW Start Idle =Read Temp? Read temperature data Calculate temperature Read pressure and temperature Calculate compensated pressure =Read Altitude? Pressure to altitude conversion Weather forecast decision (a) rev 4.5 Page 7 of 13

8 COMPASS ROUTINE Start Idle Wait command Measurement N =Cal Mode? Find parameters & Compensate for gain, offset Read raw data Data processing Calculate heading Check signal disturbance Y =Start? N Stop calibration (a) Y Start calibration Acknowledge EL Offsets has got? Y Y Data Read End? N N Wait data read out Wait & Hold EL ON=0.5sec Get EL offsets EL OFF=0.5sec Set ELoffset Rotate 360 o Collect data End rev 4.5 Page 8 of 13

9 OPERATING CONDITIONS Parameters Symbol Min Type Max Unit Supply Voltage VDD V Supply Current Istanddby Iconversion 2 ua Operating Temperature Top Serial Data Clock SCLK 64Hz 100 Hz o C APPLICATION NOTE: 1. For Compass Calibration o Put the unit on the level surface and hold it firmly. o Send the START CAL command and wait for the ACK signal. Read out the data. If it returns 0A0Ah, calibration is going. Otherwise, try to send the START CAL command till it s successfully received. o Backlight turns on for 0.5sec to collect its offset. (If connected) o Turn the unit in two circles slowly. o Send the STOP CAL command to complete. It will return 0A0Ah too as START CAL case to indicate reception is OK. o The module takes about 0.5sec to calculate the coefficients. Should not send any commands to it within this period. 2. Weather Forecast o Send the pressure command (2Ah) every 20mins to perform weather forecast procedure. The module will not do it automatically for less current consumption. USEFUL REFERENCES 1. PNI Magnetic Sensor: 2. INTERSEMA M5534A: rev 4.5 Page 9 of 13

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11 rev 4.5 Page 11 of 13 No Name X Y No Name X Y BAK XIN XOUT CFIN CFOUT GND VDD1 VDD2 VDD3 VDD4 CUP0 CUP1 CUP2 COM1 COM2 COM3 COM4 COM5 COM6 COM7 COM8 COM9 SEG1(K1) SEG2(K2) SEG3(K3) SEG4(K4) SEG5(K5) SEG6(K6) SEG7(K7) SEG8(K8) SEG9(K9) SEG10(K10) SEG11(K11) SEG12(K12) SEG13(K13) SEG14(K14) SEG15(K15) SEG16(K16) SEG17 SEG18 SEG19 SEG20 SEG21 SEG22 SEG23 SEG24/IOA1/CX SEG25/IOA2/RR SEG26/IOA3/RT SEG27/IOA4/RH SEG28/IOB1/ELC SEG29/IOB2/ELP SEG30/IOB3/BZB SEG31/IOB4/BZ SEG32/IOC1/KI1 SEG33/IOC2/KI2 SEG34/IOC3/KI3 SEG35/IOC4/KI4 SEG36/IOD1 SEG37/IOD2 SEG38/IOD3 SEG39/IOD4 SEG40 SEG41 RESET INT TEST EPT2001-O PAD COORDINATE

12 EPT2001-O PAD DIAGRAM rev 4.5 Page 12 of 13

13 PNI11096 PAD DIAGRAM & PIN ASSIGNMENT Die size is 2580um X 2360um (with scribe line) Pad coordinates All X and Y coordinates refer to the center of the die PAD # PAD NAME X (um) Y (um) PAD 1 VSTBY -655 PAD5-PAD1 Y (um) PAD 26 PAD 2 PAD 3 PAD 4 SCLK MISO MOSI PAD 5 SSNOT PAD 6 AVDD (-655,) (650,) PAD 7 PAD 8 PAD 9 AVSS APZDRV APZIN PAD 10 ANZIN PAD 11 ANZDRV -893 center of die(0,0) X (um) PAD 12 PAD 13 PAD 14 APYDRV APYIN DVDD PAD 15 ANYIN 237 PAD 16 ANYDRV 357 PAD 17 APXDRV 802 PAD 18 APXIN (-1134,) PAD 19 ANXIN PAD9-PAD17 PAD 20 PAD 21 ANXDRV DVSS PAD 22 COMP 1126 PAD 23 RESET 1008 PAD 24 DRDY 887 Remark : substrate flooting PAD 25 DHST 768 PAD 26 REXT 650 PNI part number index PNI part number Description pad Die pin SOIC pin MLF rev 4.5 Page 13 of 13