Texas Instruments DRV-ACC16-EVM User manual

User's Guide
SLOU402–June 2015
DRV-ACC16-EVM Accelerometer User’s Guide
The DRV-ACC16-EVM is a three-axis accelerometer for use in lab acceleration or vibration testing of
haptic feedback systems. The accelerometer allows vibrations to be quantified making haptic feedback
evaluation, reporting, and comparisons easier.
This document contains instructions and general guidelines for using the DRV-ACC16-EVM and
measuring acceleration.
Features
• Measure X, Y, and Z acceleration simultaneously using three independent analog outputs
• Connect to oscilloscope for simple acceleration readings
• Up to 16 gpeak acceleration measurements
• Small size and flex cable, minimize interference with natural motion of the system
Kit Contents
• DRV-ACC16-EVM accelerometer board
• Micro-USB cable for power
• Texas Instruments Black Carrying and Storage Case
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Contents
1 Overview...................................................................................................................... 3
2 Getting Started............................................................................................................... 4
3 Converting Voltage to Acceleration........................................................................................ 6
4 Determining the Axis of Vibration.......................................................................................... 7
5 Mounting Guidelines......................................................................................................... 9
6 Mounting an Actuator for Testing.......................................................................................... 9
7 Example Waveforms....................................................................................................... 10
8 Screw Hole Dimensions................................................................................................... 11
9 Schematic, Layout, and Bill of Materials ................................................................................ 12
List of Figures
1 Board Connections .......................................................................................................... 3
2 3M Tape on Backside of DRV-ACC16-EVM ............................................................................. 4
3 Attach Accelerometer to Vibrating Object ................................................................................ 4
4 DRV-ACC16-EVM - Measurement Board ................................................................................ 5
5 AC-Coupled Accelerometer ................................................................................................ 6
6 Accelerometer Conversion Voltage ....................................................................................... 6
7 Acceleration Axis............................................................................................................. 7
8 ERM Axes of Vibration...................................................................................................... 7
9 Y and Z Axes Acceleration Measurement................................................................................ 7
10 Z-Direction LRA.............................................................................................................. 8
11 Z-Axis Acceleration Measurement......................................................................................... 8
12 Piezo Module................................................................................................................. 8
13 X Axis Acceleration Measurement......................................................................................... 8
14 LRA Mounting Stack Up .................................................................................................... 9
15 Click and Release Effect .................................................................................................. 10
16 Ramp Up and Pulsing Effect.............................................................................................. 11
17 Screw-Hole Footprint ...................................................................................................... 11
18 DRV-ACC16-EVM Schematic ............................................................................................ 12
19 DRV-ACC16-EVM Top Overlay .......................................................................................... 13
20 DRV-ACC16-EVM.......................................................................................................... 13
21 DRV-ACC16-EVM Top Layer............................................................................................. 13
22 DRV-ACC16-EVM Bottom Layer......................................................................................... 13
23 DRV-ACC16-EVM Bottom Solder........................................................................................ 13
24 DRV-ACC16-EVM Drill Drawing.......................................................................................... 14
25 DRV-ACC16-EVM Board Dimensions................................................................................... 14
26 DRV-ACC16-EVM Fabrication Drawing................................................................................. 15
List of Tables
1 DRV-ACC16-EVM Specifications.......................................................................................... 3
2 Board Power Requirements................................................................................................ 4
3 Power Requirements When Bypassing LDO............................................................................. 4
4 Adhesive Transfer Tape for Mounting Actuators ........................................................................ 9
5 Bill of Materials ............................................................................................................. 16
2DRV-ACC16-EVM Accelerometer User’s Guide SLOU402–June 2015
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X Y Z
VDD GND GND GND
USB Power
Accelerometer
Attach Small Board to
Vibrating Object Using
Adhesive Tape on the
Bottom
Connect Oscilloscope Probes to X, Y, of Z Axis
www.ti.com Overview
1 Overview
There are various types of accelerometers available with different measurement ranges, thresholds,
precision, and accuracy, but in general, they all convert mechanical vibration into an electrical signal,
which can then be converted to acceleration.
The DRV-ACC16-EVM can measure acceleration up to 16 g(“g” is the acceleration due to Earth’s gravity
or 9.81 m/s2). The EVM converts the acceleration from mechanical movement to mV at a rate of 57 mVpeak
per gpeak. This means that every 57 millivolts of peak voltage equals 1 gof peak acceleration and 114
mVpeak equals 2 g’s of peak acceleration.
1.1 Required Equipment and Materials
• DRV-ACC16-EVM accelerometer board
• Micro-USB cable for power
• Oscilloscope for measuring voltage
• Adhesive transfer tape (see Mounting Guidelines)
1.2 Quick Start Connections
Figure 1. Board Connections
1. Attach the small accelerometer board to the vibrating object
2. Connect an oscilloscope to test points X, Y, and/or Z
3. Provide USB 5-V power
1.3 DRV-ACC16-EVM Specifications
Table 1 lists the DRV-ACC16-EVM specifications.
Table 1. DRV-ACC16-EVM Specifications
Value Units
Board Size (Total) 15 x 290 mm
Board Size (Accelerometer Only) 16.6 x 15 mm
Cable / Flex Length 203 mm
Interface Analog -
VDD 3.5 – 5.5 V
Acceleration Range ±16 gpeak
Bandwidth (X, Y channels) 1600 Hz
Bandwidth (Z channel) 550 Hz
Noise Density 300 µg/√Hz rms
Conversion Ratio 57 mVpeak /gpeak
DC Offset (at 0 g) 1.5 V
Typical Temperature Dependency (-25°C to 70°C) < 3 mg
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Overview www.ti.com
1.4 Power Requirements
The accelerometer board has the following electrical specifications:
Table 2. Board Power Requirements
Value Units
USB-5V 3.5 – 5 V
IDD 10 mA
The VS, accelerometer supply voltage, determines the ratio of acceleration to voltage conversion. There is
an on-board LDO that converts USB-5 V to 3 V for the accelerometer. The LDO can be bypassed, if
required.
Table 3. Power Requirements When Bypassing LDO
Value Units
VS1.8 – 3.6 V
IDD (VS= 3 V) 350 µA
2 Getting Started
The following instructions should be used for placing, mounting, and measuring acceleration with the
DRV-ACC16-EVM.
1. Attach the small accelerometer board to the surface of the vibrating object. Use the 3M tape adhesive
on the bottom of the board to attach it to the surface.
Figure 2. 3M Tape on Backside of Figure 3. Attach Accelerometer to Vibrating
DRV-ACC16-EVM Object
2. Place the vibrating object on a soft surface such as packing foam, bubble wrap, silicone, or gel
material so that the object does not rattle or move when vibrating on the table. The surface should
mimic the object’s final operating environment. See Mounting an Actuator for Testing for additional
information.
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www.ti.com Getting Started
3. Connect an oscilloscope to the X, Y, and/or Z axis test points on the measurement board. See
Determining the Axis of Vibration for additional instructions.
Figure 4. DRV-ACC16-EVM - Measurement Board
4. Apply power to the board by connecting the micro-USB cable to a USB power source such as a
computer or USB charger.
5. AC couple the measurement channels on the oscilloscope and reduce the “V/div” to 50–100 mV. The
“V/div” may need to be adjusted later.
6. As the object vibrates, the acceleration should appear as a sine wave on the oscilloscope.
7. Convert the voltage to units of gravity. The conversion ratio is shown in Equation 1:
57 mVpeak = 1 gpeak (1)
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57 mV
1 G
Measured Voltage Corresponding Acceleration
=
peak
V
Acceleration (g) 57 mV
DC Coupled Accelerometer
1.5 V
57 mV
AC Coupled Accelerometer
57 mV
0 V
Converting Voltage to Acceleration www.ti.com
3 Converting Voltage to Acceleration
The output voltage of the three accelerometer channels has a DC offset of 1.5 V at 0 g. The channels of
the DRV-ACC16-EVM can be AC coupled to only show changes in acceleration. This is recommended for
measuring the acceleration of haptic systems.
Figure 5. AC-Coupled Accelerometer
To calculate the acceleration, take the peak voltage of a single accelerometer output and divide by 57 mV.
Every 57 mV of peak voltage corresponds to 1 gof peak acceleration.
(2)
Vpeak – measured peak voltage on test point X, Y, or Z.
Figure 6. Accelerometer Conversion Voltage
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X
Y
Z
Oscilloscope
www.ti.com Determining the Axis of Vibration
4 Determining the Axis of Vibration
The orientation of the accelerometer can be determined by the 3-axis label on the small accelerometer
board. The direction of the arrows corresponds to the axis which the acceleration is measured. The Z-
direction is measured normal to, or coming out of, the board.
Figure 7. Acceleration Axis
For haptic applications, the axis of vibration is determined by the motion of the actuator. Take for example
a DC motor that spins around the X axis and creates force in the Y and Z axes. In this case, measure
vibration by connecting to the Y and Z test points of the accelerometer.
The axis of vibration can often be found in the actuator datasheet; if not, the axis is usually easily
determined by measuring all axes and finding the axis with the highest acceleration. Below are example
diagrams of ERM, LRA, and Piezo actuators and their axes of vibration.
NOTE: Not all actuators will have these same axes of vibration.
4.1 Eccentric Rotating Mass
The ERM motor in Figure 8 spins around the X axis and produces rotational vibration in the YZ plane.
Acceleration can be observed on the Y and Z accelerometer channels.
Figure 8. ERM Axes of Vibration Figure 9. Y and Z Axes Acceleration Measurement
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X
Y
Z
Oscilloscope
Y
X
Vibration
Z
X
Y
Z
Oscilloscope
Determining the Axis of Vibration www.ti.com
4.2 Linear Resonant Actuator
The following LRA motor (Figure 10) moves along the Z axis and produces vibration only on the Z axis.
Acceleration can be observed on the Z accelerometer channel.
Figure 10. Z-Direction LRA Figure 11. Z-Axis Acceleration Measurement
4.3 Piezo
Figure 12 illustrates a piezo module. A Piezo module is made using a thin piece of piezo (a piezo bender),
a mass, and a mechanical housing. The piezo bender and mass will move side-to-side when a high-
voltage sine wave is applied to the module’s input terminals.
Figure 12. Piezo Module Figure 13. X Axis Acceleration Measurement
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Case or Chassis
Adhesive
Transfer Tape
Cushion Tape
Linear Resonant
Actuator (LRA)
Actuator Support
Structure or Wall
www.ti.com Mounting Guidelines
5 Mounting Guidelines
In general, actuators should be mounted in an application using a combination of adhesion and
compression. The adhesive ensures the actuator remains in place and the compression mitigates
manufacturing tolerances and ensures that the vibration is transferred to the body of the device.
Figure 14. LRA Mounting Stack Up
Actuators are often mounted using an adhesive transfer tape from 3M. This double-sided tape is very
strong and intended to withstand a long lifetime of vibration. Many actuator manufacturers provide the
option to include the adhesive tape on the actuator for production builds.
Table 4. Adhesive Transfer Tape for Mounting Actuators
Part Number Manufacturer Description
3-5-468MP 3M Adhesive transfer tape
Alternatively, some ERM and LRA actuators can be soldered to the PCB board directly to ensure long
lasting vibration performance; however, care must be taken to ensure that vibration is transferred from the
PCB to the chassis of the device.
6 Mounting an Actuator for Testing
The acceleration of an actuator often needs to be measured outside of the final system or application to
compare actuator strengths, run life-tests, or create haptic effects. The best way to measure acceleration
is to mount the actuator on a fixture that has similar mass to the final application. We call this a haptic test
fixture. To do this:
1. Create a test fixture that has a similar size and weight as the final application. An aluminum or similar
material block works well for most applications.
2. Place the actuator in a similar location as it would appear in the final application and attach it to the
mass using strong adhesive tape, epoxy, or glue.
3. Place the test fixture on a material that can isolate the vibration such as a piece of foam or a silicone
gel. The mechanical isolation prevents rattling and transferring vibration to the table. Test the material
and make sure it roughly mimics the final application environment.
4. Place the accelerometer board on the fixture using the adhesive tape, near the actuator and begin
measuring.
To measure the acceleration of an actuator for use inside a smartphone, place the actuator on a 100 g
block that has a similar size and shape as the phone. Next, place the block on a piece of packing or ESD
foam to represent a hand, which is where a phone is normally held. Finally, measure the acceleration of
the block on the foam and compare it to when a person holds it in their hand.
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= =
´peak
149.2 mVpp
Acceleration 1.309
2 57 mVp g
Example Waveforms www.ti.com
7 Example Waveforms
The following waveforms are acceleration measurements taken with an LRA using the DRV2605L Haptic
Driver. The blue waveform is the acceleration and the orange waveform is the output voltage of the
DRV2605L.
Figure 15. Click and Release Effect
Equation 3 is the measured acceleration calculation for Figure 15.
(3)
The peak-to-peak voltage of the accelerometer voltage waveform is divided by 2 to obtain the peak
voltage and then divided by 57 mVp to calculate the acceleration.
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