Analog Devices ADXL345 manual REAL-TIME Measurement TAB

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Evaluation Board User Guide

REAL-TIME MEASUREMENT TAB

The Real-Time Measurement tab configures the inertial sensor evaluation system and the ADXL345 for real-time acceleration monitoring. The tab contains an oscilloscope-like interface that you can use to view the output of the accelerometer and adjust the relevant parameters, such as bandwidth, range, and offset (see Figure 12).

009-08119 Figure 12. Real-Time Measurement Tab

Within the Real-Time Measurement tab, additional tabs exist for displaying the output in terms of least significant bits (LSBs) or acceleration in g’s. In the Output – LSB tab, the output range can be adjusted by using the graph tools in the upper right corner or by selecting the x-axis (labeled Sample) or y-axis (labeled Output [LSB]) limits and typing a new value. For example, selecting 1024 on the y-axis and typing 2048 adjusts the scale to show +2048 LSBs to −1024 LSBs.

The configuration section is at the bottom of the Real-Time Measurement tab. In the Data Rate and Resolution box, the output data rate and g range can be adjusted. Selecting the Full-Resolutioncheckbox places the part into full-resolution mode where the scale factor is fixed. Deselecting this checkbox places the part into fixed 10-bit mode. For more information about the operation of the part, refer to the ADXL345 data sheet.

UG-015

The Self Test button toggles the self-test bit of the ADXL345. When self-test is activated, the sensor beam is deflected. The electronics detect this by means of a shift in all three axes. When self-test is enabled, the indicator next to the Self Test button is lit. Clicking the Self Test button when self-test is enabled turns the self-test feature off and causes the Self Test indicator to dim. Self-test is enabled as long as the indicator is lit.

The ADXL345 provides three offset registers that are used for calibration and offset adjustment. On the Real-Time Measurement tab, these registers are easily accessible for programming offset values. This can be done in the Offset Adjustment box by typing a value into the text box below the corresponding axis knob or by clicking and holding the knob and rotating it on the screen with the mouse cursor. The value entered is directly written into the offset registers.

After configuration, you can begin real-time measurement by clicking the Start Meas button. This causes many of the options and tabs to be grayed out or to disappear, to prevent software conflicts, until the Stop Meas button is clicked. The accelerometer output data then begins to flow across the screen at the selected output data rate.

Up to the last 8192 samples (x-, y-, and z-axis) of accelerometer output data can be saved to a .txt file. Each file created contains a header with the date, bias values, and accelerometer data, in LSBs, aligned in tab-delimited columns. To save the data, you must enable the Save Data button. Click this button and type in or select a file name with a .txt extension.

Each time a measurement is performed, the new data is appended to the old data. This means that saving data also saves old data, if new data is less than 8192 samples, unless the old data is first cleared. The data saved to a file is the LSB data; therefore, the Output – LSB window must be cleared so that old data is not saved. To clear the Output – LSB window, right-click the x-axis (labeled Sample) in the space between Sample and the window and select the Clear Chart option.

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Contents General Description FeaturesTable of Contents Software Configuration Inertial Sensor Evaluation System SetupADXL345 satellite are configured as shown in Figure Hardware ConfigurationTo flash the Iseb microcontroller, follow these steps UPDATING/REPAIRING the Iseb FirmwareUG-015 Configuration TABREAL-TIME Measurement TAB Interrupt Configuration Tab Interrupt Configuration TABPower Consumption Tab Power Consumption TABTemperature Tab Temperature TABESD Caution Evaluation Board User GuideRev Page 12