AN-1041 APPLICATION NOTE One Technology Way P.O. Box 9106 Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 Fax: 781.461.3113 www.analog.com iSensor IMU Quick Start Guide and Bias Optimization Tips by Mark Looney INTRODUCTION The iSensor IMU products include ADIS1636x and ADIS1640x. DRILL AND INSERT These multi-axis, inertial sensing systems provide a basic 1.5mm PIN 2 (HOLE PLACEMENT building block for many different motion analysis and control INACCURACY MAY REQUIRE USE OF DRILL AND TAP FOR UNDERSIZED PIN). applications (for example, navigation and platform stabilization). M2 SCREW AS REQUIRED 2. 4 PHYSICAL MOUNTING AND HANDLING BSC The iSensor IMU package has two basic parts for handling and installation into a system: an aluminum baseplate and a flexible connector (see Figure 1). The aluminum baseplate provides four mounting tabs, which accommodate a number of attachment approaches. Figure 2 and Figure 3 offer a simple method, which 26.700 27.700 BSC BSC uses two M2 or 2-56 machine screws to secure the baseplate to 10 the system printed circuit board. It also provides an option for using the precision alignment holes to tighten initial sensor HOLE 2. SEE SAMTEC 8.350 alignment, with respect to the systems inertial reference frame MOUNTING DRAWING FOR CLM SERIES SOCKET. in the yaw axis. Note that the dimensions in Figure 3 assume that the baseplate attaches to the same surface that has the 0.500 BSC 2 electrical mating connector. 16.810 2 4 BSC THE LOCATION OF THE MATING CONNECTOR RELATIVE TO THE ALIGNMENT PINS MAY BE PLACED 0.75mm FROM THIS DIMENSION AS DESIRED. PLACING THIS FURTHER OUT WILL HAVE LESS BEND/STRESS RELIEF IN THE FLEX. Figure 3. Suggested Mounting Hole Locations Applications that anticipate high shock and vibration may require more elaborate attachment systems to eliminate mechanical resonance, but the two-screw approach provides a simple starting point to begin data collection in parallel with mechanical system design. Figure 4 provides the pad layout pattern used for the mating connector (Samtec CLM-112-02- Figure 1. IMU Package Style LM-D-A) on the ADISUSBZ evaluation system. 1.588mm 0.4334 11.0 HOLE AND SLOT 0.019685 FOR ALIGNMENT 0.5000 0.0240 0.610 PINS, 2 EACH (TYP) 0.054 1.37 DRILL AND TAP HOLE FOR 0.1800 2mm (2-56) 0.0394 1.00 4.57 SCREW, 2 EACH 0.0394 1.00 0.022 DIA (TYP) NONPLATED 0.022 DIA THRU HOLE (TYP) THRU HOLE 2 NONPLATED THRU HOLE Figure 2. Two-Screw Mounting Approach, with Alignment Pins Figure 4. Suggested Layout and Mechanical Design for Mating Connector Rev. 0 Page 1 of 4 08403-001 08403-002 08403-003 08403-004AN-1041 Application Note IMU INSTALLATION AND REMOVAL SPI INTERFACE IMU installation follows a two-step sequence: Table 2 provides a list of typical configuration settings that master processors require for SPI communication with iSensor 1. Secure the baseplate using machine screws. IMUs. These settings are normally in control registers. For 2. Press the connector into its mate. example, the SPI BAUD, SPI CTL, and SPI FLG registers serve For removal, gently pry the connector from its mate, using a this purpose in the ADSP-BF533 processor family. small slot screwdriver. Then, remove the screws and lift the part Table 2. Generic Master Processor SPI Settings up. Never attempt to unplug the connector by pulling on the Processor Setting Description plastic case or baseplate. While very reliable in normal Master operation, the flexible connector can break when subjected to The iSensor IMUs operate as slaves. unreasonable handling. When broken, there are no repair SCLK Rate 2 MHz Normal mode, SMPL PRD 7:0 0x09. options for the flexible connector. SPI Mode 3 CPOL = 1 (polarity), CHPA = 1 (phase). MSB-First Mode Bit sequence. ELECTRICAL HOOK-UP 16-Bit Mode Shift register/data length. When power is applied, the iSensor products start up and begin Data communication requires firmware-level register manage- producing data, independent of user inputs. Figure 5 provides a ment. Placing a command on DIN involves writing to the transmit hook-up diagram, which accommodates power, ground, four buffer register (SPI TDBR in the ADSP-BF533). Acquiring serial signals, and a data-ready signal. The data-ready signal output data from DOUT involves reading the receive buffer typically drives an interrupt service routine in the master register (SPI RDBR in the ADSP-BF533). processor, which ensures data coherency while optimizing processor resources. OPTIMIZING BIAS ACCURACY AND STABILITY I/O LINES ARE COMPATIBLE WITH All of the iSensor IMUs include a factory calibration that provides 3.3V OR 5V LOGIC LEVELS 5V substantial improvements in bias accuracy over most MEMS VDD gyroscopes. Some environmental conditions (such as tempera- 10 11 12 SYSTEM ture cycling and installation) can cause minor shifts in gyroscope PROCESSOR ADIS1636x/ SS 6 CS SPI MASTER output bias. A single-point adjustment can address these shifts ADIS1640x SPI SLAVE and restore the entire calibration, including the temperature 3 SCLK SCLK correction that comes with some parts. This involves measuring 5 MOSI DIN the zero-rotation gyroscope output and writing the opposite value into its offset register. There are three basic options for 4 MISO DOUT executing the single-point adjustment in the gyroscopes: autonull, 7 IRQ DIO1 precision autonull, and manual calibration. The following conditions/settings help assure optimum accuracy during this 13 14 15 process: 1. Sample rate = 819.2 SPS (SMPL PRD 7:0 = 0x01) Figure 5. Electrical Hook-Up Diagram 2. Thermal stability Reading the temperature output registers can help Table 1. Generic Master Processor Pin Names and Functions determine when this happens. Pin Name Function 3. Zero rotation (including vibration) SS Slave select Take a small sample of data and make sure that the output IRQ Interrupt request noise is in agreement with the data sheet. For example, MOSI Master output, slave input with no filtering, the ADIS1636x and ADIS1640x should MISO Master input, slave output have less than 1/sec rms of noise on their gyroscopes. SCLK Serial clock Rev. 0 Page 2 of 4 08430-005