Acceleration due to gravity can be calculated by measuring the time taken by an object to fall under gravity from a given height. A metal ball is held by an electromagnet powered by OD1. A loudspeaker generates an electrical signal when the ball hits the surface. It is amplified and given to SEN via a PN junction diode. The time from a falling edge on OD1 to a rising edge on SEN is measured using software.
The value of g is given by g= 2*h/t^2. The time is measured within one millisecond error. The experiment is repeated with different heights to eliminate the systematic error due to the finite time taken by the coil to release the ball.