While working on his masters degree in controls and robotics, Hack-A-Day reader [Kenn Sebesta] developed a cheap method for digitally reading analog gauges. This method was necessitated by needing to take over 3000 measurements using a dial indicator during his thesis work. The system is implemented in Matlab and uses a webcam to take a picture of the gauge. Once picture is taken it goes through several steps: First, it is reduced to a single color. Then, edge extraction is used to find the lines. Next, the lines are thickened. Finally, the Hough transform is applied to find the longest line: the needle. All that is left to do is measure the arc back to the zero point and match it to your scale. Using this method Kenn’s laptop can take 4 measurements per second.
