This circuit it is count the acceleration from -1000mg up to +1000mg. Can be used in lot of applications like cars, elevators, ramps and more.
The measurement of acceleration becomes with the use of IC from Analog Devices, the ADXL202. The particular element contains 2 autonomous vertical between them sensors, for the measurement in two axes. For the particular application becomes use of only it's one. Acceleration meter measures dynamic or static acceleration from –2g until 2g (where g is the acceleration of gravity) and when this is equal to zero, exit is a signal PWM, with Duty Cycle 50%. As long as the acceleration increases, increases also the Duty Cycle, with biggest response the 75% (in the 2g), while for acceleration –2g, the Duty Cycle is 25%. As conclusion from more, has that for change 1g, is altered also the Duty Cycle of exit at 12,5%.
The measurement of Duty Cycle of response of acceleration meter becomes with the help of Timer1 (16 bit). The period of signal of expense, has been fixed in the 1,12 msec. The frequency of oscillation of microcontroller is in the 3,6864 MHz and this means that it's each circle of access lasts 0,27 * 10 -6 sec. Using timer1, in frequency of measurement ck/1, the biggest feasible counted time is the 65536 * 0.27 * 10 -3 msec = 17.778 msec, which is bigger than period (1,12 msec). So, any price Duty Cycle it is possible to be measured.