A program for a PIC 18 series to measure the accelerometer. Intended to be on a car. You should open the schematic file with Proteus (labcenter.com) and compile the main.c file with CCS compiler.
Our micro-controller has to be programmed so we can capture (we will use the Capture pins for this) the two PWM's generated by the accelerometers, and perform the following tasks:
1.- Calculate the tilting angle in that axis: knowing the duty of the PWM to calculate the tilt angle we do as follows: 2∗π∗arcsin((X1/(X1+X2)−0.5)∗8) . So after capturing the PWM's duty we should do this operation.
2.- Average the last three angle measurements: The accelerometers measurements are usually noisy, so we want to average the last 5 measures. To do this we simply create a five element array and a pointer to this array so we can keep track of where the last angle was added. In the following task, when I talk about angles I am referring to the average of the angles.
3.- Print the tilt angles to an LCD: A standard two-lines LCD is connected to the uController and we have to output the tilting values previously calculated.
4.- Generate two PMW's encoding the angle: Once we have calculated the angles we have to also encode them into PWM with a duty of 50% representing an angle of zero degrees and for each degree negative or positive we should add or subtract respectively 1% of the duty. That way an angle of 13 deg. should be encoded as a duty of 63%. This PWM should have a total period of 1 msec.
5.- Record the angles in a EEPROM: To keep historical data, it can be useful in case of accident or other problems, sort of simple black box for cars. To communicate with the EEPROM we will use i2C .
You should be able to compile it with CCS compiler or equivalent. I am not including the lcd.h file because it has a copyright by the CCS compiler so you may want to comment out the printf lines in the main file if you don't want to compile it with this functionality beacuse you dont have that file.
If you want to check the whole project visit http://fsanmartin.me/blog/?p=73