PNI SENtral MandM User Manual

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Page 1

Item

Sensors

Part #

White M&M

none (Sentral only)

13734

Orange M&M

BMI055+AK8963

13771

Red M&M

MPU6500+AK8963

13763

Green M&M

LSM330+AK8963

13736

Yellow M&M

LSM9SD0

13738

Blue M&M

LSM330+RM3100

13759

SENtral M&M

Motion & Measurement Modules

General Description

PNI’s SENtral M&M motion and measurement modules provide accurate heading and orientation data in a small, lowpower-consumption, and easy-to-integrate package. A module incorporates the SENtral motion coprocessor, a magnetometer, an accelerometer, and a gyroscope, with different SENtral M&M versions comprising different sensor models.

Unlike other inertial measurement units (IMUs) requiring extensive sensor fusion algorithm development and sensor calibration work, the Sentral M&M modules are pre-engineered to provide high accuracy motion tracking and heading data. And this is obtained at a fraction of the power used by any other solution on the market.

The SENtral M&M comes ready to integrate

into a user’s system. Designed with SMT

soldering in mind, the pins are on an industry-standard 3 mm pitch. The on-board

EEPROM contains SENtral’s configuration

file and this automatically uploads into SENtral RAM when powered up. Communication is via I2C protocol.

Features

 All-in-one motion & orientation tracking

module, incorporates the SENtral motion coprocessor, 3-axis gyroscope, 3-axis accelerometer, and 3-axis magnetometer.

 Low power consumption.  11x11 mm footprint and SMT design for

ease of integration into a user’s system

 Multiple test points for debugging and

evaluating performance.

 Multiple versions with different sensors.

Applications

 Personal Navigation & LBS  Gaming & Augmented Reality  Movement Science & Fitness

Ordering Information

With the SENtral M&M modules you can quickly and easily incorporate industryleading motion-tracking and orientation

measurement in your mobile device. We’re

sure you’ll be impressed.

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Table of Contents

1 PRODUCT OVERVIEW ............................................................................................... 3

1.1 SENTRAL FEATURES AND BENEFITS ........................................................ 3

1.2 SENTRAL M&M SYSTEM OVERVIEW .......................................................... 4

2 SENTRAL SPECIFICATIONS ..................................................................................... 6

2.1 PERFORMANCE CHARACTERISTICS ......................................................... 6

2.2 ELECTRICAL CHARACTERISTICS ............................................................... 6

3 INTERFACE ................................................................................................................. 8

3.1 I2C TIMING ...................................................................................................... 9

3.2 I2C HOST INTERFACE (HOST BUS) ........................................................... 10

3.2.1 I2C Transfer formats ......................................................................... 11

3.3 I2C SENSOR INTERFACE (SENSOR BUS) ................................................. 12

3.4 HOST INTERRUPT/GPIO LINES ................................................................. 12

4 OPERATION .............................................................................................................. 13

4.1 POWER-UP ................................................................................................... 14

4.2 INITIAL REGISTER SET-UP ......................................................................... 14

4.3 RUNNING IN NORMAL OPERATION .......................................................... 16

4.3.1 Error .................................................................................................. 18

4.3.2 Read Results .................................................................................... 18

4.4 STANDBY STATE ......................................................................................... 19

4.5 PASS-THROUGH STATE ............................................................................. 20

4.6 TROUBLESHOOTING .................................................................................. 22

4.6.1 Hardware-Related Error Conditions ................................................. 22

4.6.2 Software-Related Error Conditions ................................................... 23

5 PACKAGE INFORMATION ....................................................................................... 25

6 ASSEMBLY GUIDELINES ......................................................................................... 27

APPENDIX I – CONVERTING QUATERNIONS .................................................................... 29

APPENDIX II – PARAMETER TRANSFER ............................................................................ 31

APPENDIX III – MEASURING CURRENT CONSUMPTION ................................................. 37

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List of Figures

Figure 1-1: SENtral M&M Module Reference Schematic ......................................................... 4

Figure 3-1: I2C Timing Diagram ................................................................................................ 9

Figure 3-2: I2C Slave Write Example ...................................................................................... 11

Figure 3-3: I2C Slave Read Example, with Repeated START................................................ 11

Figure 3-4: I2C Slave Write Register Address Only ................................................................ 11

Figure 3-5: I2C Slave read register from current address ....................................................... 11

Figure 4-1: SENtral Initialization Sequence ............................................................................ 13

Figure 4-2: SENtral Operational States .................................................................................. 13

Figure 4-3: SENtral Normal Operation Flow ........................................................................... 18

Figure 6-1: SENtral Orange, Red, Green, & Yellow M&M Mechanical Drawing .................... 25

Figure 6-2: SENtral White M&M Mechanical Drawing............................................................ 25

Figure 6-3: SENtral Blue M&M Mechanical Drawing.............................................................. 26

Figure 7-1: SENtral Orange, Red, Green, & Yellow M&M Solder Pad Layout ....................... 27

Figure 7-2: SENtral White M&M Solder Pad Layout .............................................................. 27

Figure 7-3: SENtral Blue M&M Solder Pad Layout ................................................................ 28

Figure A2-1: Parameter Load Process ................................................................................... 32

Figure A2-2: Parameter Retrieve Process ............................................................................. 33

Figure A3-1: SENtral Blue M&M Zero-Ohm Resistor Location .............................................. 37

List of Tables

Table 2-1: Performance Characteristics ................................................................................... 6

Table 2-2: Absolute Maximum Ratings .................................................................................... 6

Table 2-3: Operating Conditions............................................................................................... 7

Table 3-1: SENtral M&M Module Pin Assignments .................................................................. 8

Table 3-2: I2C Timing Parameters .......................................................................................... 10

Table 4-1: Configuration File Upload from EEPROM Registers ............................................ 14

Table 4-2: Registers for Initial Set-up ..................................................................................... 15

Table 4-3: Normal Operation Registers .................................................................................. 17

Table 4-4: Results Registers .................................................................................................. 19

Table 4-5: Standby Registers ................................................................................................. 20

Table 4-6: Pass-Through Registers........................................................................................ 21

Table 4-7: Hardware-Related Error Indications ...................................................................... 22

Table 4-8: Software-Related Error Indications ....................................................................... 23

Table 4-9: ErrorRegister Indications ....................................................................................... 23

Table 4-10: RAMVersion Register Values .............................................................................. 24

Table A2-1: Registers Used for Parameter Transfer .............................................................. 31

Table A2-2: Parameter Numbers............................................................................................ 34

Table A2-3: DriverID & AlgorithmID Definition ....................................................................... 36

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1 Product Overview

The SENtral M&M Motion and Measurement Module is a castellated printed-circuit assembly that makes it easy to quickly integrate a complete motion-sensor-fusion system into a mobile device. A module incorporates the SENtral Motion Coprocessor, a magnetometer, an accelerometer, and a gyroscope, with different SENtral M&M versions integrating different sensor models. The SENtral Motion Coprocessor manages and uses data from the three sensors to provide reliable motion tracking and an accurate compass heading, while consuming about 1% of the power of a comparable ARM-based sensor fusion microprocessor. SENtral outputs Euler angles (aka heading, pitch, and roll), quaternions, and sensor data. Quaternions uniquely define orientation and, unlike Euler angles, do not experience a singularity (i.e. gimbal lock) when pointing straight up. They easily can be converted to Euler angles, the rotation vector, and the rotation matrix (aka DCM), as discussed in Appendix I.

1.1 SENtral Features and Benefits

At the heart of the SENtral M&M module is PNI’s revolutionary SENtral Motion Coprocessor. Listed below are some of the features and benefits of this device.

 Low power consumption. Offloads sensor processing from the less efficient host

CPU, consuming <1% of the power of a Cortex M0 running a comparable sensor fusion algorithm. Provides the ability to tailor the tradeoff between power consumption and motion-tracking performance.

 Industry-leading heading accuracy. Unparalleled heading accuracy for consumer

electronics applications.

 Continuous hard and soft-iron auto-calibration. Unlike other motion-tracking

products, SENtral calibrates for both hard-iron and soft-iron magnetic distortion. Specifically, soft-iron distortion is quite difficult to correct, and can contribute up to 90° of error. It can be caused by materials widely used in mobile and consumer electronic devices, such as EMI shielding tape and other shielding. Additionally, since a host system’s magnetic signature can change over time and temperature, SENtral’s continuous auto-calibration ensures accuracy over time.

 Magnetic anomaly compensation. With SENtral, heading and motion tracking is

unaffected by short-term magnetic anomalies, such as rebar in buildings, desks, speakers etc., that can easily throw off the accuracy. SENtral establishes if a transient magnetic anomaly is present and compensates for this.

 Sensor flexibility. SENtral works with most common consumer electronics motion

sensors, so designers can choose the sensors most appropriate for their systems.

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 Small form-factor. 1.6x1.6x0.5 mm chip-scale package on 0.4 mm pitch. Uses little

PCB real estate, allowing for painless integration.

 I2C interface. Uses industry-standard I2C protocol in a low-power implementation to

interface to the sensors and the host, so system integration is straightforward. Standard, Fast, Fast Plus, and High Speed are supported on the host bus.

 Outputs. SENtral natively outputs Euler angles (heading, pitch, and roll),

quaternions, rotational velocity, linear acceleration, and magnetic field.

 Pass-Through allows for direct communication with devices on the I2C sensor bus.

1.2 SENtral M&M System Overview

Figure 1-1 provides a reference schematic for SENtral M&M modules. While this diagram applies for most versions of the SENtral M&M, the White and Blue M&M modules differ from what is shown. Specific schematics for each module are available from PNI on request. How to interface with the SENtral M&M is covered in more detail in Section 3.

Figure 1-1: SENtral M&M Module Reference Schematic

A few points on diagram:

 The layout shows a discrete magnetometer, accelerometer, and gyroscope. SENtral

M&M modules generally incorporate a combo sensor that combines the gyroscope and accelerometer into a single device or all three sensors into a single device.

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 SENtral acts as a slave on a host system I2C bus. This does not need to be a dedicated

bus, although it is shown this way in the schematic.

 The SCLM and SDAM lines can be used to monitor SENtral’s I2C sensor bus, but

this is not necessary. These lines are optional and may be left unconnected.

 If the host will poll SENtral, rather than running in an interrupt-driven manner, it is

not necessary to connect GPIO[6], the host interrupt line, to the host system.

 GPIO[4] is intended for future use and currently serves no purpose. This can be left

unconnected.

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Parameter

Minimum

Typical

Maximum

Units

Heading Accuracy

° rms

Output Data Rate

200

400

Parameter

Symbol

Minimum

Maximum

Units

Supply Voltage

VDD

-0.3

+3.6

VDC

Input Pin Voltage

VIN

GND – 0.3

VDD + 0.3

VDC

Storage Temperature

-50°

+150°

2 SENtral Specifications1

2.1 Performance Characteristics

Table 2-1: Performance Characteristics

2.2 Electrical Characteristics

Table 2-2: Absolute Maximum Ratings

CAUTION:

Stresses beyond those listed above may cause permanent damage to the device. These are stress ratings only. Operation of the device at these or other conditions beyond those indicated in the operational sections of the specifications is not implied.

Footnote

1. Specifications subject to change.

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Parameter

Symbol

Min

Typ

Max

Units

Digital Supply Voltage – Sensors &

EEPROM

DVDD

1.71

AVDD

VDC

Supply Voltage – SENtral

DVDD2

1.6 3.3

VDC

Analog Supply Voltage – Sensors

AVDD

2.4 3.6

VDC

Power-On Reset Threshold

POR

1.0 VDC

High Level Input Voltage

VIH

0.7*VDD

VDD

VDC

Low Level Input Voltage

VIL 0

0.3*VDD

VDC

High Level Output Current, VOH = VDD – 0.3V

IOH

-1

Low Level Output Current, VOL = 0.3V

IOL 1 mA

I2C Interface Data Rate1 Host Bus

3400

kbits/sec

Sensor Bus

1000

kbits/sec

Pass-Through

400

kbits/sec

Operating Temperature

TOP

-40

+25

+85

Table 2-3: Operating Conditions

Footnote:

1. SENtral’s I2C Host Interface supports Standard, Fast, Fast Plus, and High Speed Modes. High Speed Mode (3400 kHz) is supported with a reduced range of VDD and bus

capacitance. SENtral’s I

Modes. Pass-Through state, which connects the sensor bus and host bus, supports Standard and Fast Modes.

C sensor bus interface supports Standard, Fast, and Fast Plus

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Pin Name

Description

M&M Orange,

Red, Green, &

Yellow Pin#

M&M

White

Pin #

M&M

Blue

Pin #

DVDD

Digital Supply Voltage – Sensors &

EEPROM

DVDD2

Supply Voltage – SENtral

AVDD

Analog Supply Voltage – Sensors

GND

Ground 8 D2

SCLS

I2C host bus SCL clock line

SDAS

I2C host bus SDA data line

SDAM

I2C sensor bus SDA data line

SCLM

I2C sensor bus SCL clock line

GPIO[0]

SENtral Accelerometer Interrupt

GPIO[1]

SENtral Magnetometer Interrupt

GPIO[2]

SENtral Gyroscope Interrupt

GPIO[3]

Reserved

GPIO[4]

Reserved

GPIO[5]

Reserved

GPIO[6]

Host Event Interrupt

SA0

Slave Address Pin 0

VCAP

Regulator Capacitor

Reserved

Reserved (not connected)

1, 12, 13

3 Interface

The SENtral M&M pin-out is given in Table 3-1. Pin-outs also are given alongside the device mechanical drawings in Section 5. See Table 2-3 for the operating ranges of DVDD, DVDD2, and AVDD. A discussion of the communication interface follows the table.

Table 3-1: SENtral M&M Module Pin Assignments

Communication with the host processor is via SENtral’s I2C host interface, where the SENtral M&M acts as a slave device and the host’s processor acts as the master. The host interrupt line informs the host system when SENtral has updated measurement data. The SENtral Motion Coprocessor on the SENtral M&M module communicates with the module’s sensors over the sensor bus, where SENtral is the I2C master and the sensors are slave devices.

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SENtral’s I2C interfaces comply with NXP’s UM10204 specification and user manual, rev 04. Standard, Fast, Fast Plus, and High Speed modes of the I2C protocol are supported by SENtral’s I2C host interface. Below is a link to this document.

http://www.nxp.com/documents/user_manual/UM10204.pdf

3.1 I2C Timing

SENtral’s I2C timing requirements are set forth below, in Figure 3-1 and Table 3-2. For the timing requirements shown in Figure 3-1, transitions are 30% and 70% of VDD.

Figure 3-1: I2C Timing Diagram

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Standard

Fast

Fast Plus

Units

Symbol

Parameter

Min

Max

Min

Max

Min

Max

SCL

SCL Clock

100 0 400

1000

kHz

SDA & SCL Rise

Time

1000

300 120

SDA & SCL Fall Time

300

20*(VDD/

5.5V)

300

20*(VDD/

5.5V)

120

LOW

LOW period of SCL

Clock

4.7 - 1.3 - 0.5

s

HIGH

HIGH period of SCL

Clock

4.0 - 0.6 - 0.26

s

HD;STA

Hold time (repeated)

START

4.0 - 0.6 - 0.26

s

HD;DAT

Data hold time

0 - 0 - 0

s

SU:DAT

Data set-up time

250 - 100 - 50 - ns

SU;STA

Set-Up time for

repeated Start

4.7 - 0.6 - 0.26

s

SU;STO

Stop set-up time

4.0 - 0.6 - 0.26

s

BUF

Bus free time between

STOP & START

4.7 - 1.3 - 0.5

s

Table 3-2: I2C Timing Parameters

3.2 I2C Host Interface (Host Bus)

The host will control the SENtral M&M on the host bus via SENtral’s I2C host interface. The host interface consists of 2 wires: the serial clock, SCLS, and the serial data line, SDAS. Both lines are bi-directional. SENtral is connected to the host bus via the SDAS and SCLS pins, which incorporate open drain drivers within the device. Note the SENtral M&M module incorporates 4.7 kΩ pull-up resistors on the host bus clock and data lines, so if the host system also incorporates pull-up resistors on these line the resistors will act in parallel.

The SENtral M&M’s 7-bit I2C slave address is 0x28 (0b0101000). The shifted address is 0x50.

Data transfer is always initiated by the host. Data is transferred between the host and SENtral serially through the data line, SDAS, in an 8-bit transfer format. The transfer is synchronized by the serial clock line, SCLS. Supported transfer formats are single-byte read, multiple-byte read, single-byte write, and multiple-byte write. The data line can be driven

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START

SLAVE ADDRESS

ACK

DATA TO REGISTER (N)

ACK

DATA TO REGISTER (N+1)

ACK

STOP

A0 0 0

R0 0 D7

D0 0 D7

D0 0 P

From Host to SENtral

------------ Data Transferred (n bytes + acknowledge) ------------

From SENtral to Host

START

SLAVE ADDRESS

ACK

START

SLAVE ADDRESS

ACK

DATA FROM REGISTER (N)

NACK

STOP

A0 0 0

R0 0 SR

A0 1 0

D0 1 P

Data Transferred

(n bytes + acknowledge)

START

SLAVE ADDRESS

ACK

STOP

A0 0 0

R0 0 P

START

SLAVE ADDRESS

ACK

DATA FROM REG. (N)

ACK

DATA FROM REG. (N+1)

NACK

STOP

A0 1 0

D0 0 D7

D0 1 P

From Host to SENtral

-------------- Data Transferred (n bytes + acknowledge) --------------

From SENtral to Host

either by the host or SENtral. Normally the serial clock line will be driven by the host, although exceptions can exist when clock-stretching is implemented in Pass-Through State.

3.2.1 I2C Transfer formats

Figure 3-2 illustrates writing data to registers in single-byte or multiple-byte mode.

Figure 3-2: I2C Slave Write Example

The I2C host interface supports both a read sequence using repeated START conditions, shown in Figure 3-3, and a sequence in which the register address is sent in a separate sequence than the data, shown in Figure 3-4 and Figure 3-5.

Figure 3-3: I2C Slave Read Example, with Repeated START

Figure 3-4: I2C Slave Write Register Address Only

Figure 3-5: I2C Slave read register from current address

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3.3 I2C Sensor Interface (Sensor Bus)

Understanding how the sensor interface operates is not necessary when using the SENtral M&M module. However, understanding the sensor interface is useful if there is a need to communicate directly with a sensor or the EEPROM in Pass-Through state.

The SENtral Motion Coprocessor on the SENtral M&M module communicates with the module’s accelerometer, gyroscope, and magnetometer over the module’s sensor bus, where SENtral is the I2C master and the sensors are slave devices. On the sensor bus, SENtral initiates data transfer and generates the serial clock. The two wires comprising the sensor bus are SDAM, the serial data line, and SCLM, the serial clock. Both are bidirectional and driven by open drain transistors within SENtral. These can be monitored by the host, but

should not be written to by the host. Each line is attached to a 4.7 kΩ pull-up resistor. SENtral’s I2C sensor interface supports Standard mode with a rate up to 100 kbit/s, Fast

mode with a rate up to 400 kbit/s, and Fast Plus mode with a rate up to 1000 kbit/s.

3.4 Host Interrupt/GPIO Lines

GPIO[6] provides an interrupt to the host whenever a defined event occurs. Exactly which types of events will trigger an interrupt are set by the EnableEvents register, which is discussed in Section 4.2 This interrupt line can be used to signal the host that new results are available for reading. Alternately, the host may poll SENtral’s EventStatus register, discussed in Section 0, to determine if any events of interest have been updated. If polling will be

used, PNI recommends polling on a regular interval such that an error event will be identified in a timely manner.

GPIO[4] is not currently used, and generally should be left unconnected. This is also true for GPIO[3] and GPIO[5], which are only accessible on the SENtral White M&M.

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4 Operation

Figure 4-1 provides a flow chart of the SENtral M&M module’s initialization process, and a discussion of this process follows in Section 4.1 For the registers, all multi-byte elements are

stored and transmitted using the Little Endian convention: the least significant byte is stored at the lowest address and transmitted first over the I2C bus.

Figure 4-1: SENtral Initialization Sequence

Once the initialization sequence is complete, there are three states in which SENtral may reside: Normal Operation, Standby, and Pass-Through. Figure 4-2 indicates the recommended way to get from one state to another, and these states are discussed in detail in Sections 4.2 and 0 (Normal Operation), 4.4 (Standby), and 4.5 (Pass-Through).

Figure 4-2: SENtral Operational States

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Address

SentralStatus

0x37

[0] EEPROM. 1 = EEPROM detected [1] EEUploadDone. 1 = EEPROM upload completed [2] EEUploadError. 1 = Calculated CRC of EEPROM is

incorrect. Only valid when EEUploadDone = 1. [3] Idle. 1 = Device in Unprogrammed or Initialized state. [4] NoEEPROM. 1 = No EEPROM detected.

ResetReq

0x9B

[0] ResetRequest. 1 = Emulate a hard power down/power up.

4.1 Power-Up

After powering up or issuing a ResetReq command, SENtral automatically initializes the registers and loads the SENtral Configuration File from the onboard EEPROM, as indicated in Figure 4-1. The Configuration File contains information specific to the particular SENtral M&M flavor, and is discussed more thoroughly in the SENtral Motion Coprocessor Technical Datasheet. Once the upload is complete, SENtral enters Initialized State and waits for instructions from the host.

Table 4-1: Configuration File Upload from EEPROM Registers

The host should confirm a successful EEPROM upload by following the steps below:

 Read the value from the SentralStatus register.  Check bit [0], the EEPROM bit, to ensure an EEPROM is detected by SENtral.  Check bit [1], the EEUploadDone bit. If this is ‘0’ then the Configuration File upload

is not complete, and reread the SentralStatus register until bit [1] = 1.

 Once bit [1] = 1, check bit [2], the EEUpload Error bit. If this is ‘0’, then the upload

was successful.

If the Configuration File upload failed, send a Reset command by writing 0x01 to the ResetReq register or power off/power on the device. If the issue persists, refer to the SENtral Motion Coprocessor datasheet for debugging hints.

4.2 Initial Register Set-Up

After the initialization process is complete, it is necessary to configure a few of SENtral’s registers before running in Normal Operation. These registers are given in Table 4-2.

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Address

MagRate

0x55

Requested magnetometer output data rate

AccelRate

0x56

Requested accelerometer output data rate divided by 10

GyroRate

0x57

Requested gyroscope output data rate divided by 10

QRateDivisor

0x32

Along with GyroRate, establishes output data rate for

quaternion data.

AlgorithmControl

0x54

[0] 1 = StandbyEnable

0 = Disable Standby State (return to Normal Operation)

[1] RawDataEnable. 1 = Raw data provided in MX, MY,

MZ, AX, AY, AZ, GX, GY, & GZ. 0 = Scaled sensor data.

[2] HPRoutput. 1 = Heading, pitch, and roll output in QX,

QY, & QZ. QW = 0.0. 0 = Quaternion outputs.

EnableEvents

0x33

‘1’ indicates an interrupt to the host will be generated for

the event. [0] CPUReset. Non-maskable [1] Error [2] QuaternionResult [3] MagResult [4] AccelResult [5] GyroResult

Table 4-2: Registers for Initial Set-up

Perform the following operations to run SENtral as desired.  Set the sensor output data rates (ODRs): MagRate, AccelRate, and GyroRate. If a

sensor rate is set to 0x00, SENtral will shutdown the sensor and disable SENtral background calibration. There are two major points regarding setting these registers: o The AccelRate and GyroRate register values should be 1/10th the desired ODR,

while the MagRate value should match the desired ODR. For example, if the desired ODR is 30 Hz for the magnetometer, 100 Hz for the accelerometer, and 200 Hz for the gyroscope, then the respective register values should be 0x1E (30d), 0x0A (10d), and 0x14 (20d).

o The actual accelerometer and gyro ODRs are limited to the ODRs supported by

the specific sensors. If the AccelRate or GyroRate register values do not correspond to a supported ODR, then the next highest ODR will be used. For instance, if the GyroRate register is set to 0x14, which corresponds to 200 Hz, but the gyro supports 95 Hz, 190 Hz, and 380 Hz, then the actual gyro ODR will be 380 Hz since this is the closest supported rate above that requested by the register.

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 Establish the quaternion output data rate, where the quaternion output data rate equals

GyroRate divided by QRateDivisor. The default for QRateDivisor is 0x00, which is interpreted as ‘1’ and results in the quaternion output data rate equaling GyroRate.

 Establish how SENtral’s orientation and sensor data is to be output. The

AlgorithmControl register allows the user to select either quaternion or Euler angles (heading, pitch, and roll) for orientation outputs, and either scaled or raw sensor data outputs. The defaults are quaternions and scaled sensor data.

 Establish which events will trigger an interrupt to the host by configuring the

EnableEvent register. PNI specifically recommends enabling bit [1], the Error interrupt bit, in addition to whichever other interrupts the user wants.

Example steps to do this are below:  Write 0x1E0A0F to the MagRate register. Since SENtral automatically increments to

the next register, this also populates the AccelRate and GyroRate registers. This sets MagRate to 100 Hz, AccelRate to 100 Hz, and GyroRate to 150 Hz.

 Write 0x02 to the QRateDivisor Register. This sets the quaternion output data rate to

be half the GyroRate. This step is optional, as the default register value of 0x00 sets the quaternion output data rate equal to GyroRate.

 Write 0x06 to the AlgorithmControl register. This enables heading, pitch, and roll

orientation outputs and raw sensor data outputs. This step is optional, as the default register value of 0x00 results in outputs of quaternions and scaled sensor data.

 Write 0x07 to the EnableEvents register. This sets the host to receive interrupts from

SENtral whenever the quaternion results registers (QX, QY, QZ, and QW) are updated, an error has been detected, or SENtral has been Reset but the Configuration File has not been uploaded. If the host regularly will poll SENtral, rather than run in an interrupt-driven manner, it is not necessary to set the EnableEvents register.

Note: It is necessary to set the MagRate, AccelRate, AND GyroRate registers to non-zero values for the SENtral algorithm to function properly and to obtain reliable orientation and scaled sensor data. If a [Sensor]Rate register is left as 0x00 after power-up, or is changed to 0x00, this effectively disables that sensor within the SENtral algorithm. Also, the CalStatus, MagTransient, and AlgorithmSlow bits become undefined.

4.3 Running in Normal Operation

After performing the steps listed above, SENtral is ready to start generating orientation data. The registers used to run in Normal Operation are given in Table 4-2, the steps to follow comes after this, and a flow diagram is given in Figure 4-3.

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Address

HostControl

0x34

[0] 1 = RunEnable 0 = Enable Initialized State (Standby State generally

is preferred since enabling Initialized State resets the

SENtral algorithm, including calibration data.)

EventStatus

0x35

‘1’ indicates a new event has been generated. [0] CPUReset [1] Error [2] QuaternionResult [3] MagResult [4] AccelResult [5] GyroResult

Table 4-3: Normal Operation Registers

Below are the steps to follow when operating in Normal Operation state. a) Write 0x01 to the HostControl register. This sets the RunEnable bit to ‘1’ and

enables the sensors and the SENtral algorithm.

b) If operating in an interrupt-driven mode, then the host waits until it receives an

interrupt signal from SENtral. Alternatively the host may operate on a polling basis, rather than an interrupt-driven basis, in which case the interrupt line may not be used.

c) Once an interrupt is received by the host or the host otherwise decides to read new

data, read the EventStatus register.

d) Interpret and act on the EventStatus register in the priority shown in Figure 4-3. If bit

[1], the Error bit, is ‘1’, see Section 4.3.1. If bits [2], [3], [4], or [5], the Results bits,

are ‘1’, see Section 4.3.2. Bit [0], the CPUReset bit, should never be ‘1’, since this bit only can be ‘1’ after a Reset or powering up and prior to loading the Configuration

File, and on the SENtral M&M module loading of the Configuration File is automatically performed after powering up.

e) Repeat steps c and d until new orientation data is not needed and/or the host decides

to enter a different state.

Reading the EventStatus register clears it. It is possible for more than one bit position to

be ‘1’ in the EventStatus register, especially if the host does not always read the EventStatus

register after receiving an interrupt. Similarly, if multiple bits are set to ‘1’ in the EventStatus register, once the register is read all the bits will be set to ‘0’. For this reason the

EventStatus register should be processed in the priority shown in Figure 4-3, as information will be cleared for events that are not handled.

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Figure 4-3: SENtral Normal Operation Flow

A discussion of how to handle the events follows.

4.3.1 Error

In the event of an error, SENtral will trigger an error interrupt and SENtral will enter Standby State. See the Section 4.6 for recommendations on Troubleshooting and/or reset SENtral by sending 0x01 to the ResetReq register, at address 0x9B.

4.3.2 Read Results

The Results Registers’ addresses, formats, and full-scale ranges are given below in Table 4-4. For an explanation of how to convert quaternions to the rotation vector, the rotation

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Name

Address

(Hex)

Description

Format

Full-Scale Range

00 – 03

Normalized Quaternion – X, or Heading

Float32

0.0 – 1.0, or ±

04 – 07

Normalized Quaternion – Y, or Pitch

Float32

0.0 – 1.0, or ±/2

08 – 0B

Normalized Quaternion – Z, or Roll

Float32

0.0 – 1.0, or ±

0C – 0F

Normalized Quaternion – W, or 0.0

Float32

0.0 – 1.0

QTime

10 – 11

Quaternion Data Timestamp

UInt16

0 – 2048 msec

12 – 13

Magnetic Field – X Axis, or Raw Mag Data

Int16

±1000 µT when scaled

14 – 15

Magnetic Field – Y Axis, or Raw Mag Data

Int16

±1000 µT when scaled

16 – 17

Magnetic Field – Z Axis, or Raw Mag Data

Int16

±1000 µT when scaled

MTime

18 – 19

Magnetometer Interrupt Timestamp

UInt16

0 – 2048 msec

1A – 1B

Linear Acceleration – X Axis, or Raw Accel Data

Int16

±16 g when scaled

1C – 1D

Linear Acceleration – Y Axis, or Raw Accel Data

Int16

±16 g when scaled

1E – 1F

Linear Acceleration – Z Axis, or Raw Accel Data

Int16

±16 g when scaled

ATime

20 – 21

Accelerometer Interrupt Timestamp

UInt16

0 – 2048 msec

22 – 23

Rotational Velocity – X Axis, or Raw Gyro Data

Int16

±5000°/s when scaled

24 – 25

Rotational Velocity – Y Axis, or Raw Gyro Data

Int16

±5000°/s when scaled

26 – 27

Rotational Velocity – Z Axis, or Raw Gyro Data

Int16

±5000°/s when scaled

GTime

28 – 29

Gyroscope Interrupt Timestamp

UInt16

0.0 – 2.048 sec

matrix, or Euler angles (heading, pitch, and roll), see Appendix I. The resolution is 32 kHz for all timestamps.

Note: All multi-byte elements are stored and transmitted using the Little Endian convention: the least significant byte is stored at the lowest address and transmitted first over the I2C bus.

Table 4-4: Results Registers

4.4 Standby State

In Standby State overall system power consumption is dramatically reduced because both the SENtral algorithm and the sensors are shut down. Table 4-5 provides the registers associated with Standby State.

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Address

AlgorithmControl

0x54

[0] 1 = StandbyEnable 0 = Disable Standby State

AlgorithmStatus

0x38

[0] 1 = SENtral in Standby State 0 = SENtral not in Standby State

Table 4-5: Standby Registers

The steps to enter and exit Standby State are given below:

 Write 0x01 to the AlgorithmControl register. This places SENtral in Standby State.  Read the AlgorithmStatus register. If bit [0] is ‘1’, then SENtral is in Standby State.

This step is optional.

 When you are ready to exit Standby State, write 0x00 to the AlgorithmControl

 Read the AlgorithmStatus register. If bit [0] is ‘0’, then SENtral is not in Standby

State. This step is optional.

4.5 Pass-Through State

In Pass-Through State, SENtral’s sensor and host interfaces are connected by internal switches so the host system can communicate directly with the sensors or EEPROM. To enter Pass-Through State, SENtral first either should be in Standby or Initialized State. Consequently, in Pass-Through State the SENtral algorithm, host interrupt line, and sensors are disabled, unless a sensor is directly turned on by the host. When exiting Pass-Through State, SENtral will return to its prior state.

Note: When entering Pass-Through State the sensor’s registers retain the values established by SENtral, and when exiting Pass-Through State any register changes will be retained.

Uses for the Pass-Through State include:

 Direct control of sensors, if desired.  Debugging.  Communication with the dedicated EEPROM, if implemented. Specifically, if a new

Configuration File is generated, the host can write this into the EEPROM when in Pass-Through State, as discussed in the SENtral Motion Coprocessor datasheet.

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Address

AlgorithmControl

0x54

[0] 1 = StandbyEnable 0 = Disable Standby State

AlgorithmStatus

0x38

[0] 1 = SENtral in Standby State 0 = SENtral not in Standby State

PassThroughControl

0xA0

[0] 1 = Enable Pass-Through State 0 = Disable Pass-Through State

PassThroughStatus

0x9E

[0] 1 = SENtral in Pass-Through State. 0 = SENtral not in Pass-Through State.

Since operating in Pass-Through State requires stopping the SENtral algorithm, PassThrough State is not recommended for accessing sensor data unless reliable heading data is not required. If sensor data and reliable heading data are both desired, they can both be accessed during Normal Operation from the Results Registers, as given in Table 4-4.

Table 4-6 provides the registers associated with Pass-Through State.

Table 4-6: Pass-Through Registers

The steps to go in and out of Pass-Through State are given below.

 Write 0x01 to the AlgorithmControl register. This places SENtral in Standby State.  Write 0x01 to the PassThroughControl register. This places SENtral in Pass-Through

State.

 Read the PassThroughStatus register. If bit [0] is ‘1’, then SENtral is in Pass-

Through State. This step is optional.

 When you are done in Pass-Through State, write 0x00 to the PassThroughControl

 Write 0x00 to the AlgorithmControl register. This takes SENtral out of Standby State

and normally will place it back into Normal Operation.

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Address

Error Indication

EventStatus

0x35

[0] 1 = CPURest. SENtral Configuration

File needs uploading. See Section 4.1.

SentralStatus

0x37

[2] 1 = EEUploadError. Issue with

uploading from the dedicated EEPROM. See Section 4.1.

MagRate

0x55

0x00 – Value lost

AccelRate

0x56

0x00 – Value lost

GyroRate

0x57

0x00 – Value lost

4.6 Troubleshooting

This section provides guidance in troubleshooting SENtral, and is divided into hardwarerelated and software-related errors.

4.6.1 Hardware-Related Error Conditions

Possible indications of a hardware-related problem are given below in Table 4-7.

Table 4-7: Hardware-Related Error Indications

In the event of such errors, SENtral will enter Standby State, shut down the sensors, and generate an interrupt to the host. Possible reasons for hardware-related errors include problems with the EEPROM upload, power transients detected by power management, and errors in software detected by Watchdog. Often the error can be cleared by sending the ResetReq command.

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Address

Error Indication

EventStatus

0x35

[1] 1 = Error.

SensorStatus

0x36

[0] MagNACK. 1 = NACK from magnetometer [1] AccelNACK. 1 = NACK from accelerometer [2] GyroNACK. 1 = NACK from gyroscope [4] MagDeviceIDErr. 1 = Unexpected DeviceID from

magnetometer [5] AccelDeviceIDErr. 1 = Unexpected DeviceID from

accelerometer

[6] GyroDeviceIDErr. 1 = Unexpected DeviceID from

gyroscope.

SentralStatus

0x37

[3] 1 = Idle. SENtral in Initialized State.

ErrorRegister

0x50

Non-zero value indicated an error. See Table 4-9.

RAMVersion

0x72, 0x73

Unexpected Configuration File revision level.

Value

Error Condition

Response

0x00

No error

0x80

Invalid sample rate selected

Check sensor rate settings.

0x30

Mathematical Error

Check for software updates

0x21

Magnetometer initialization failed

This error can be caused by a wrong

driver, physically bad sensor connection, or incorrect I2C device address in the driver

0x22

Accelerometer initialization failed

0x24

Gyroscope initialization failed

0x11

Magnetometer rate failure

This error indicates the given sensor

is unreliable and has stopped producing data.

0x12

Accelerometer rate failure

0x14

Gyroscope rate failure

4.6.2 Software-Related Error Conditions

Possible indications of software-related errors are given below in Table 4-8:

Table 4-8: Software-Related Error Indications

If the ErrorRegister indicates a non-zero value, then the value provides additional information on the sensor that is causing a problem, as given in Table 4-9.

Table 4-9: ErrorRegister Indications

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If the RAMVersion register values do not correspond to the expected Configuration File revision level, as given in Table 4-10, certain features or functions that are expected to be

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0x72 Register

Value

0x73 Register

Value

RAM Version

(Hex / Decimal)

Config File

Revision

0x04

0x0C

0x0C04 / 3076

1.0

0xD5

0x0C

0x0CD5 / 3285

1.1

0x37

0x0E

0x0E02 / 3639

1.2

available may not be available, or they may not function as expected. This normally can be remedied by generating the latest Configuration File revision level using the SENtral Configuration Tool and then loading this into the onbaord EEPROM, as discussed in the SENtral Technical Datasheet.

Table 4-10: RAMVersion Register Values

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5 Package Information

Figure 5-1: SENtral Orange, Red, Green, & Yellow M&M Mechanical Drawing

Figure 5-2: SENtral White M&M Mechanical Drawing

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Figure 5-3: SENtral Blue M&M Mechanical Drawing

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6 Assembly Guidelines

Figure 6-1: SENtral Orange, Red, Green, & Yellow M&M Solder Pad Layout

Figure 6-2: SENtral White M&M Solder Pad Layout

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Figure 6-3: SENtral Blue M&M Solder Pad Layout

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Appendix I – Converting Quaternions

SENtral outputs orientation data in quaternions, using a North-East-Down (NED) convention. This is done to avoid the singularities inherent in using Euler angles (heading, pitch, and roll), and because the fusion algorithms are easier to implement with quaternions. However, normally quaternions are not the desired final output format. Most end users will want heading, pitch, and roll, while Android looks for a rotation vector and generally uses a rotation matrix for orientation. Plus, Android and Win8 both expect data to be presented in the East-North-Up (ENU) convention. This appendix discusses how to convert SENtral’s output quaternions into these other output formats.

Converting from NED to ENU

While the North-East-Down (NED) convention is common in many industries, both Android and Windows 8 use the East-North-Up convention. Below is the equation to convert from NED to ENU.

Heading, Pitch, and Roll

Most end users will want orientation data reported as heading, pitch, and roll. Below are the Excel transformation equations. Note that for other programs, such as Matlab, the ATAN2 arguments may be reversed.

 Heading = atan2[(Qx2 – Qy2 – Qz2 + Qw2), 2*(QxQy + QzQw)]  Pitch = asin[-2*(QxQz – QyQw)]  Roll = atan2[(–Qx2 – Qy2 + Qz2 + Qw2), 2*(QxQw + QyQz)]

Where:

 Results are in radians.  The quaternions are the outputs from SENtral in NED convention.  Heading increases as the device rotates clockwise around a positive Z axis, and the

range is 0° – 360°. (i.e. it matches what you would expect on a compass.)

 Pitch increases when pitching upward and the range is ±180°.  Roll increases when rolling clockwise and the range is ±90°.

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Qw2 + Qx2 – Qy2 – Qz2

2*(Qx*Qy + Qw*Qz)

2*(Qx*Qz – Qw*Qy)

R =

2*(Qx*Qy – Qw*Qz)

Qw2 – Qx2 + Qy2 – Qz2

2*(Qy*Qz + Qw*Qy)

2*(Qx*Qz + Qw*Qy)

2*(Qy*Qz – Qw*Qy)

Qw2 – Qx2 – Qy2 + Qz2

Rotation Vector

The rotation vector is the first three elements of the quaternion output, Qx, Qy, and Qz. The fourth element, Qw, is not included in the rotation vector. The rotation vector in ENU convention will be the first three elements of Q

Rotation Matrix, or Direction Cosine Matrix (DCM)

, discussed above.

ENU

The rotation matrix, also known as the direction cosine matrix (DCM), can be established from the quaternion output using the following conversion. Q

values can be substituted

ENU

to give the rotation matrix with an ENU convention.

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Address

Access

Format

Description

AlgorithmControl

0x54

R/W

[7:0]

[0] StandbyEnable. 1 = Enable Standby state [1] RawDataEnable. 1 = Raw data provided in

MX, MY, MZ, AX, AY, AZ, GX, GY, & GZ. 0 = Scaled sensor data.

[2] HPRoutput. 1 = Heading, pitch, and roll

output in QX, QY, & QZ. QW = 0.0. 0 = Quaternion outputs.

[7] ParamTransfer. 1 = Enable Parameter

Transfer.

LoadParamByte0

0x60

R/W

Float 8

Parameter value to be loaded – LSB

LoadParamByte1

0x61

R/W

Float 8

Parameter value to be loaded – LSB + 1

LoadParamByte2

0x62

R/W

Float 8

Parameter value to be loaded – MSB – 1

LoadParamByte3

0x63

R/W

Float 8

Parameter value to be loaded – MSB

ParamRequest

0x64

R/W

[7:0]

Bits [0] – [6] provide the parameter number to be uploaded or retrieved.

[7] Load/Save bit. 1 = Load, 0 = Save.

ParamAcknowledge

0x3A

R/O

[7:0]

Bits [0] – [6] provide the parameter number that was uploaded or retrieved.

[7] Load/Retrieve bit. 1 = Load, 0 = Retrieve.

RetrieveParamByte0

0x3B

R/O

Float 8

Parameter value read from Sentral – LSB

RetrieveParamByte1

0x3C

R/O

Float 8

Parameter value read from Sentral – LSB + 1

RetrieveParamByte2

0x3D

R/O

Float 8

Parameter value read from Sentral – MSB – 1

RetrieveParamByte3

0x3E

R/O

Float 8

Parameter value read from Sentral – MSB

Appendix II – Parameter Transfer

Note: Implementing the parameter transfer process is not necessary when using SENtral, but can be useful for enabling a warm start, for setting the sensor ranges to non-default values, and/or for reading the device driver IDs.

This appendix provides the protocol for implementing SENtral’s parameter transfer process. A parameter transfer involves the host either loading parameter values into SENtral, or retrieving parameter values currently used by SENtral.

Register Usage

Table A2-1 provides the registers used for the parameter transfer process.

Table A2-1: Registers Used for Parameter Transfer

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The parameter transfer process is invoked and terminated by appropriately setting the ParamTransfer bit in the AlgorithmControl register. Ten (10) registers are used for the transfer and for handshaking between SENtral and the host. One set of four registers is allocated to upload a parameter value to SENtral, and another set of four registers is used to retrieve a currently saved parameter from SENtral. Values shorter than four bytes can be transferred using only some of the registers. Two registers implement the handshake mechanism between SENtral and the host. Note that data is stored in little Endian format.

Parameter Load

Figure A2-1 shows the Parameter Load process by which the host loads parameter data into SENtral.

Figure A2-1: Parameter Load Process

Initially the parameter values must be written into the LoadParamByte registers followed by sending a non-zero parameter number into the ParamRequest register. The parameter numbers are given in Table A2-2. The MSB of the ParamRequest register should be set to ‘1’ to indicate a Load procedure. All five bytes can be written using a single I2C

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transaction. AFTER the first parameter is written, the ParamTransfer bit in the

AlgorithmControl register must be set to ‘1’. Sentral acknowledges receipt of a parameter

value by setting ParamAcknowledge equal to ParamRequest, and the host should check the ParamAcknowledge register after writing the first parameter.

Once SENtral acknowledges successfully uploading the first parameter, the host can begin writing the remaining parameters in a loop. Reading the ParamAcknowledge register is optional for subsequent parameters. The host terminates the load procedure by setting the ParamRequest register to 0x00 and the AlgorithmControl register’s ParamTransfer bit to ‘0’.

Parameter Retrieve

The Parameter Retrieve flowchart is given in Figure A2-2.

Figure A2-2: Parameter Retrieve Process

The process is initiated by the host writing to the ParamRequest register the desired (nonzero) parameter number. The MSB of ParamRequest register should be ‘0’ to indicate a Retrieve procedure. After writing to the ParamRequest register, the ParamTransfer bit in

the AlgorithmControl register must be set to ‘1’. Next, the host should perform repetitive

reads of the ParamAcknowledge register until it contains the requested parameter number.

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Parameter

Number

Parameter Name

ParamRequest

Value

Load

Retrieve

1 – 35

WarmStart[1] to

WarmStart[35]

0x81 to

0xA3

0x01 to

0x23

36 – 73

Reserved

SensorRange[mag:accel]

0xCA

0x4A

SensorRange[gyro]

0xCB

0x4B

DriverID[mag:accel]

0x4D

DriverID[gyro]

0x4E

AlgorithmID

0x50

Now the host can read the RetrieveParamByte registers to obtain the parameter value. Note the host can read the ParamAcknowledge and RetrieveParamByte registers using a single five-byte read transaction. Also, the RetrieveParamByte values are given in little Endian

format, such that RetrieveParamByte3 contains the least significant byte of the parameter’s

4-byte float value. The host can continue reading other parameters by varying (normally incrementing) the parameter number contained in the ParamRequest registers. Reading the ParamAcknowledge register is optional for subsequent parameters. The procedure is terminated by the host writing 0x00 to the ParamRequest and AlgorithmControl registers.

Interleaving Parameter Load and Retrieve

The host can interleave the Parameter Load and Parameter Retrieve processes during a single process invocation. This can be done for each parameter by setting the MSB bit of the ParamRequest register appropriately. Note that SENtral can be copying a new value into a RetrieveParamByte register while a Parameter Load operation is requested. Interleaving can be utilized by the host as an additional check that the parameter value was updated correctly.

Parameters

The parameter numbers and associated names are given below in Table A2-2. A discussion on the WarmStart, SensorRange, and DriverID parameters follows.

Table A2-2: Parameter Numbers

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WarmStart

A significant number of parameters are used in the SENtral algorithm as it executes, and these parameters are refined as the SENtral device is used. These include

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parameters associated with SENtral’s continuous background calibration function and

gyro bias correction. When SENtral is powered down or otherwise re-initialized, these parameters also are re-initialized and the parameter refinement process must start over. The parameter transfer process provides the ability to save these parameters to the host as they are refined, and to reload them if the parameters within SENtral are re-initialized. Thus, if the WarmStart parameters periodically are retrieved from SENtral and saved by the host, it is possible to effectively warm-start SENtral after it is re-initialized by reloading the WarmStart parameters into SENtral that previously were saved to the host.

To effectively enable a warm-start process, it is necessary to periodically save all 35 WarmStart parameters, and to reload all of them after SENtral is re-initialized.

SensorRange

The dynamic ranges of the sensors used in conjunction with SENtral normally are set as part of the Configuration File. Typically the gyroscope will be set to 2000 dps, the accelerometer to ±2 g or ±4 g, and the magnetometer to ±1 T. However, there may be instances when it is desirable to change the dynamic range. For instance, if SENtral will be used in an application with frequent shock, such as jogging, it may be necessary to increase the accelerometer range to something greater than ±4 g.

SensorRange[mag:accel] loads or retrieves the magnetometer range data in ParamByte0 and ParamByte1, while the accelerometer range data is in ParamByte2 and ParamByte3. For example, a likely readout for SensorRange[mag:accel] in the 4x RetrieveParamByte registers is 0xE8030200, corresponding to a magnetometer dynamic range of 0x03E8 (±1000 T) and an accelerometer dynamic range of 0x0002 (±2 g). SensorRange[gyro] loads or retrieves the gyroscope range in ParamByte0 and ParamByte1, while ParamByte2 and ParamByte3 are reserved and should be 0x00.

DriverID and AlgorithmID

Sensor driver and algorithm revision information can be retrieved using the Parameter Transfer process. Table A2-3 indicates how these parameters are defined. ParameterBytes 2 and 3 for Parameter Numbers 78 and 80 are 0x00 and reserved for future use.

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Parameter

Number

Parameter

Name

Parameter

Byte

Usage

DriverID[mag:accel]

Mag Driver Revision

Mag Driver ID

Accel Driver Revision

Accel Driver ID

DriverID[gyro]

Gyro Driver Revision

Gyro Driver ID

AlgorithmID

Algorithm Revision, Minor

Algorithm Revision, Major

Table A2-3: DriverID & AlgorithmID Definition

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Appendix III – Measuring Current Consumption

All SENtral M&M modules, except the White and Blue versions, have two distinct electrical supply lines. One line is for both the EEPROM and the sensors, and one is for just SENtral. The pins for these voltages are labeled DVDD and DVDD2, respectively. To measure the current on these lines, PNI recommends placing a 1 Ω resistor in series with the DVDD pin to measure combined current consumption for the EEPROM and sensors, and a 100 Ω resistor in series with the DVDD2 pin to measure current consumption by SENtral.

The SENtral Blue M&M has a single DVDD pin that supplies current for SENtral, the EEPROM and the sensors. However, the current consumption of only the SENtral Motion Coprocessor can be measured by modifying the module, as given in the two options listed below.

1. Replace a zero-ohm resistor with a 100Ω resistor and measure voltage across the resistor.

2. Remove the zero-ohm resistor, then solder wires in series with a connected ammeter.

The location of the zero-ohm resistor is given below, and a discussion of the two implementation methods follows.

Figure A3-1: SENtral Blue M&M Zero-Ohm Resistor Location

Method 1: Replace zero-ohm resistor with 100 Ω resistor.

This method provides flexibility in terms of measuring with either a voltmeter or an oscilloscope, although it may be slightly difficult to implement as holding the probes in the proper position can be tricky. As long as the resistor is ≤100 Ω, there is no need to remove it, as it should not affect performance.

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To measure average current consumption, simply touch either side of the 100 Ω

resistor with the voltmeter’s probe tips and measure the voltage drop. Convert to

current consumption using: A = 10*mV, assuming a 100 Ω resistor.

It is possible to observe the current consumption waveform using an oscilloscope. In this case, place a 100 F capacitor in parallel with the 100 Ω resistor. This reduces the measurement bandwidth so the waveform can be better observed.

Note that SENtral’s bypass capacitors are electrically connected nearest the device

after the sense resistor or the voltage meter’s resistor. This will bandlimit the

measurement to ~1.5 kHz for a 100 Ω resistor. The onboard bypass capacitance

totals 1.1 F.

Method 2: Remove zero-ohm resistor and place ammeter in series.

This method is relatively straight forward to implement, as the probes are physically soldered to the PCB. To help prevent damage to the PCB surface pads, PNI strongly recommends implementing a strain relief for the wires.

Note that the burden voltage of a typical digital multimeter (ammeter) is ~100V/A, or 100 Ω. PNI has tested such an ammeter in the Method 2 scenario and seen that it does not affect operation. Also note that negative voltages produced by transient currents are smoothed by the local bypass capacitors.

Also, it may be difficult to measure DC current using ammeters with very fast measurement times due to the periodic wake/sleep cycles of SENtral. Consequently, handheld DMMs with relatively long measurement integration times work well for making average current measurement. Precision benchtop meters with an averaging or smoothing filter also can work well.

PNI Sensor Corporation Doc #1020129 revE SENtral M&M Technical Datasheet Page 38

Page 40

Reproduction, adaptation, or translation without prior written permission is prohibited, except as allowed under copyright laws.

Revised April 2014: for the most recent version of this document visit our website at www.pnicorp.com

PNI Sensor Corporation

2331 Circadian Way

Santa Rosa, CA 95407, USA

Tel: (707) 566-2260

Fax: (707) 566-2261

Warranty and Limitation of Liability. PNI Sensor Corporation ("PNI") manufactures its Products from parts and components that are new or equivalent to new in performance. PNI warrants that each Product to be delivered hereunder, if properly used, will, for ninety (90) days following the date of shipment unless a different warranty time period for such Product is specified: (i)

in PNI’s Price List in effect at time of order acceptance; or (ii) on PNI’s web site (www.pnicorp.com) at time of order

acceptance, be free from defects in material and workmanship and will operate in accordance with PNI’s published specifications and documentation for the Product in effect at time of order. PNI will make no changes to the specifications or manufacturing processes that affect form, fit, or function of the Product without written notice to the Customer, however, PNI may at any time, without such notice, make minor changes to specifications or manufacturing processes that do not affect the form, fit, or function of the Product. This warranty will be void if the Products’ serial number, or other identification marks have been defaced, damaged, or removed. This warranty does not cover wear and tear due to normal use, or damage to the Product as the result of improper usage, neglect of care, alteration, accident, or unauthorized repair.

THE ABOVE WARRANTY IS IN LIEU OF ANY OTHER WARRANTY, WHETHER EXPRESS, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR ANY PARTICULAR PURPOSE, OR ANY WARRANTY OTHERWISE ARISING OUT OF ANY PROPOSAL, SPECIFICATION, OR SAMPLE. PNI NEITHER ASSUMES NOR AUTHORIZES ANY PERSON TO ASSUME FOR IT ANY OTHER LIABILITY.

If any Product furnished hereunder fails to conform to the above warranty, Customer’s sole and exclusive remedy and PNI’s sole and exclusive liability will be, at PNI’s option, to repair, replace, or credit Customer’s account with an amount equal to the price

paid for any such Product which fails during the applicable warranty period provided that (i) Customer promptly notifies PNI in

writing that such Product is defective and furnishes an explanation of the deficiency; (ii) such Product is returned to PNI’s service facility at Customer’s risk and expense; and (iii) PNI is satisfied that claimed deficiencies exist and were not caused by accident,

misuse, neglect, alteration, repair, improper installation, or improper testing. If a Product is defective, transportation charges for the return of the Product to Customer within the United States and Canada will be paid by PNI. For all other locations, the warranty excludes all costs of shipping, customs clearance, and other related charges. PNI will have a reasonable time to make repairs or to replace the Product or to credit Customer’s account. PNI warrants any such repaired or replacement Product to be free from defects in material and workmanship on the same terms as the Product originally purchased.

Except for the breach of warranty remedies set forth herein, or for personal injury, PNI shall have no liability for any indirect or speculative damages (including, but not limited to, consequential, incidental, punitive and special damages) relating to the use of or inability to use this Product, whether arising out of contract, negligence, tort, or under any warranty theory, or for infringement

of any other party’s intellectual property rights, irrespective of whether PNI had advance notice of the possibility of any such damages, including, but not limited to, loss of use, revenue or profit. In no event shall PNI’s total liability for all claims regarding

a Product exceed the price paid for the Product. PNI neither assumes nor authorizes any person to assume for it any other liabilities.

Some states and provinces do not allow limitations on how long an implied warranty lasts or the exclusion or limitation of incidental or consequential damages, so the above limitations or exclusions may not apply to you. This warranty gives you specific legal rights and you may have other rights that vary by state or province.

PNI Sensor Corporation Doc #1020129 revE SENtral M&M Technical Datasheet Page 39

PNI SENtral MandM User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

1 Product Overview

1.1 SENtral Features and Benefits

1.2 SENtral M&M System Overview

2 SENtral Specifications1

2.1 Performance Characteristics

2.2 Electrical Characteristics

3 Interface

3.1 I2C Timing

3.2 I2C Host Interface (Host Bus)

3.2.1 I2C Transfer formats

3.3 I2C Sensor Interface (Sensor Bus)

3.4 Host Interrupt/GPIO Lines

4 Operation

4.1 Power-Up

4.2 Initial Register Set-Up

4.3 Running in Normal Operation

4.3.1 Error

4.3.2 Read Results

4.4 Standby State

4.5 Pass-Through State

4.6 Troubleshooting

4.6.1 Hardware-Related Error Conditions

4.6.2 Software-Related Error Conditions

5 Package Information

6 Assembly Guidelines

Appendix I – Converting Quaternions

Appendix II – Parameter Transfer

Register Usage

Parameter Load

Parameter Retrieve

Interleaving Parameter Load and Retrieve

Parameters

WarmStart

SensorRange

DriverID and AlgorithmID

Appendix III – Measuring Current Consumption

Method 1: Replace zero-ohm resistor with 100 Ω resistor.

Method 2: Remove zero-ohm resistor and place ammeter in series.