Objective:
Implement the MMA8451Q accelerometer over I2C, and develop the logic for a digital angle gauge without the LCD screen. LED color is changed in response to the device orientation allowing a user to set the saw blade on a table saw to exactly 45° relative to the table. Calibrate the sensor to 0° setting to improve the accuracy by using a button connected to GPIO to indicate 0° or by sending a command over UART.
Implementation:
State machine:
State machine was implemented to change the state from calibration to angle_measurement. There are three states present:
- OBTAIN_DATA_ZERO_CALIB: This is the initial state where the accelerometer data is considered only if the default angle obtained by the accelerometer is zero.
- CALIBRATE_ANGLE: This state is entered if the calibrate command is received or the GPIO pin PD7 is made to ground
- ANGLE_DATA_DISPLAY: This expression is entered calibration in first two cases was successful. In this state the angle data is read.
The detection of signals is detected by the change of color. The following colors are used for detection:
a. Red color on the controller represents it is 30 degrees
b. Green color on the controller represents it is 45 degrees
c. Blue color on the controller represents it is 60 degrees
d. White color on the controller represents it is 90 degrees
The change of color is obtained by using PWM.
Verification:
The change of angle is manually tested by placing the sensor at angles like 30, 45 , 60 and 90 degrees. The calibration is tested manually by giving calibrate command and validating if the that angle is reading a zero. The PWM is tested by an automated test script written which tests if the LED glows correctly.
Note:
The UART configuration used was:
- Baud rate: 38400
- Parity bit: None
- Stop bit: 2