measurement of gravitational acceleration using photogate
circuit description
Overview
Transparent plastic ruler taped with black stripes of definite spacing(~5 mm) is fallen down freely through photogate. Every time interval during which two succesive stripes passed is measured using simple digital circuit and transmitted to PC through 16-bit interfacing.The results are processed by C-language program and s-t graph is obtained. This graph will be fitted to extract gravitational acceleration g.
Operation
(1) Gate, counter and display are initially resetted by pushing RESET button.
(2) Transparent ruler with black stripes is fallen freely through photogate. Once a stripe passes the photogate, it will open the GATE circuit and start counting.
(3) At every moment when each stripe passes the photogate, a very short pulse is generated. By this, latching counted time, setting FLAG, and resetting counter are performed sequentially.
(4) PC checks FLAG at every instant. When FLAG setting is detected, PC performs both counter-reading and FLAG-resetting simultaneously.
Warning
This circuit uses one-directional transmitting interface. Care must be taken so that some data should not be lost during slow hand-shaking. The interfacing system should be as fast as possible!
Circuit diagram
circuit photos
measured data
