Interface MEMS 3-Axis Accelerometer to Microcontroller

Transcription

1 1 Background ME313 Project Assignment #1 Interface MEMS 3-Axis to Microcontroller Last Updated January 3, The objective of the ME313 project is to fabricate a digital controller for a fixed-pivot, inverted pendulum. The sensor used to measure the angular position of the pendulum will be a MEMS accelerometer, and the digital microcontroller will be an Arduino Uno. In Project Assignment #1, you will interface the MEMS accelerometer to the Arduino, and use the accelerometer to measure angular position of the sensor in degrees. Required Apparatus 1. Arduino Uno R3. It is assumed each student already possesses this component. 2. ADL335 Triple Axis, breakout form vended by Sparkfun ( Provided in class " (2.54mm) Breakaway Male Header: 1x40-Pin, Straight, vended by Pololu Robotics ( Provided in class. 4. Wires with Pre-Crimped Terminals, M-F 12, vended by Pololu Robotics ( 5 Wires required, provide in class. Instructions ou are first asked to fabricate the circuit shown on the following page. In this circuit, voltages corresponding to the, and Z directions will be converted in the A0, A1, and A2 A/D channels. Please refer to the instructions after the circuit diagram.

2 2 ADL335 IOREF RESET 3.3V 5V Vin A0 A1 A2 A3 A4 A5 Arduino R3 - - AREF GND T 1 R 0 1. View the supporting videos for Project Goal and Project Assignment #1: Interface MEMS s to Arduino. 2. Solder a segment of the breakaway male header to the ADL335 accelerometer breakaway board. It will be desired to connect the wires to the header from the top side of the breakout, so make sure and place the short ends of the header through the holes and apply solder to the reverse side. 3. Connect the circuit as shown in the diagram, using the 12 wires with pre-crimped M-F terminals. 4. Write an Arduino code to read the voltages on channels A0, A1, and A2 repetitively and print integer values corresponding to the converted voltages to the serial monitor. The code should contain the following three types of statements: a. Serial.begin(9600): This statement will enable communication at 9600 baud from the Arduino through the USB into the Serial Monitor in the Arduino development application. b. analogread(n): This statement reads a voltage from the A/D channel n (n is an integer). For example, if one wanted to read channel A0, then the statement would be analogread(0). The result will be an integer ranging from 0 to 255 corresponding to the voltage on channel A0.

3 ADL335 3 c. Serial.println(x, DEC): This statement will print the variable x in decimal (DEC) format to the serial monitor. 5. Use the code developed in step 4 to generate a model to relate the voltages measured on the and accelerometers (channels A0 and A1) to the orientation angle of the accelerometer. Start the process by placing the axis edge of the accelerometer breakout board on a flat horizontal surface, and the axis pointed vertically upward. Record the integer values for the and accelerometers in the first row of the table below. Orientation of Orientation (deg) Integer Corresponding to Voltage Read on Integer Corresponding to Voltage Read on ADL335 0 ADL ADL

4 4 6. Orient the accelerometer after three 90 o rotations as shown in the table, and record the integers corresponding to the accelerometer voltage from each orientation in the appropriate row of the table. 7. Using the model V V x y K g sin V x y ox K g cos V for the accelerometers discussed in class, determine the accelerometers gains Kx, Ky and offsets Vox, Voy from the calibration data contained in the table completed in step 6. In the model, Vx and Vy are the integers corresponding to the voltages converted from the and accelerometers. An example Matlab script to determine a straight=-line model with slope m=kxg and intercept b=vox is shown below:, oy, clear call; close all; clc; Data Table Theta (degrees) Sin(theta) Vx (after A/D) So now, we will fit a straight line for Vx=m*sin(theta) + b with slope m and intercept b that will pass through the measured data. Place the data sin(theta) in a vector called s s=[ ] Place the data vx in a vector called vx vx=[ ] Perform regression to determine m and b [p,s] = polyfit(s,vx,1); m=p(1) b=p(2) The data in the example script was measured by a ME313 student. 8. Algebriacally solve the two model equations for the angle, given that Kx, Ky, Vox, Voy are known and Vx, Vy are measured. 9. Extend the code developed in step 4 to compute the orientation of the accelerometer from voltages converted from the accelerometers, and print the orientation to the serial monitor.

5 5 Required Documentation ou are required to make a video of the results of steps 4 and 9. Each video should show the apparatus, changing orientation of the accelerometer, and serial monitor output corresponding to the orientation of the accelerometer. our video should also include an audio narration, and a shot of your code. Please join the videos from steps 4 and 9, and submit to Bblearn in a single file. our file should not exceed 30MB in size.