- 1 2 Calibration When You Connect The Accelerometer To Your Breadboard And Place It On The Desk The Z Axis Points Upward 1 (167.15 KiB) Viewed 14 times
1.2 Calibration When you connect the accelerometer to your breadboard and place it on the desk, the Z axis points upwards while the X and Y axes are on a horizontal plane. At rest, the X, Y and Z-axis accelerations should ideally read Og, Og and +1g, respectively. You probably won't see these exact values. The Og acceleration may not output precisely 1.65 V, and the sensitivity may not be 3.3V/32g = 0.103 V/g. Furthermore, these offsets and sensitivities may differ from axis to axis. Instead of assuming that Og corresponds to 1.65 V, you can take a few measurements of the voltage corresponding to Og and average them to find the actual offset voltage. If you modify your voltage-to- acceleration equation using this offset, you will get better results. Similarly, you can find a better estimate of the sensitivity using your own measurements. The difference between the voltages corresponding to Og and 1g is an estimate of the accelerometer's sensitivity (change in output voltage for unit change in acceleration). BMEN 3150-Sensor Integration Page 2 In order to automate the above calibration process, you will now write a sketch that will perform the following steps. 1. At start-up, the serial monitor will display: "About to start calibration" and wait 2 seconds. 2. Then it will display "Keep accelerometer steady in horizontal position" and wait 2 seconds. The user will keep the accelerometer chip in the horizontal plane with Z-axis pointing upwards. 3. Display "Do not move" for 2 seconds. During this time, record Xout, Yout and Zout voltages at 100 msec intervals. The average values for X and Y axes are the voltages corresponding to Og for these two axes, and that for Z-axis is the voltage for 1g.
4. Display "Place accelerometer with X-axis pointing upwards" and wait for 5 seconds to allow the user to position the breadboard vertically. 5. Display "Do not move" for the next 2 seconds. During this time, record Xout and Zout voltages at 100 msec intervals. The average value for the X-axis is now the voltage corresponding to 1g, and that for Z-axis is the voltage for Og. 6. Display "Place accelerometer with Y-axis pointing upwards" and wait for 5 seconds to allow the user to position the breadboard in that position. 7. Display "Do not move" for the next 2 seconds. During this time, record Yout voltages at 100 msec intervals, the average of which is the Y-axis voltage corresponding to 1g. 8. Calculate the offset and sensitivity for the three axes and update the parameters in the equation that computes acceleration as function of the voltage measured at the ADC pin. 9. Display "Calibration complete. Now displaying acceleration data in X, Y and Z axis.". 10. The serial monitor will then continue to display the acceleration data in the serial monitor. If the user wants, they can switch to the serial plotter. Steps 1 to 9 will run only once when the microcontroller is reset. Step 10 will run continuously.