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GRAPHING THE DATA

by George Martin

Start ı How I Did It ı Background Painting ı Data Plotting ı Sources and PDF

Back in July, I talked about creating a simple data logger with a serial port to interface to a data-acquisition device using Visual Basic (VB). Remember that we could save the data to a file and I said you could load that file into a spreadsheet program and create a graph? At the time, I planned to plot the data on the screen as it was acquired, but when the time for my next column came about, I couldnıt figure it out. Well, I finally figured it out.

I actually came up with several possible solutions. I could use MSChart, which is part of the VB package. Itıs hundreds of kilobytes of code in size. Although it works fine for plotting small amounts of static data, it didnıt feel like a good match for the large amounts of dynamic data that I could be dealing with. It has too much in some areas and too little in others. Besides, with what Iıve already published, you could use a spreadsheet and publish gorgeous graphs. Graph32 is another tool recently released with VB, and is somewhat smaller than MSChart, but it still feels wrong.

I could purchase a charting package. If it was just me and I was under the gun to get a project done on time, I would probably take this path. But, fortunately, Iıve got some flexibility about when I need to be finished.

What I need is a lean, mean charting routine, one where you can see, understand, and even modify the code to suit your specific application. Monitoring a battery-charging circuit is different than monitoring a joystick force-position curve.

Two articles helped me zero in on what Iım about to present. Ward Hittıs "Write a Lean Chart Control" (Visual Basic Programmers Journal, June 1998) described the exact software I was looking for. However, he offers a GraphLite ActiveX control with no source code. So, I now knew it was possible, which was a big advantage.

In Chris Barlowıs article, "Make Forms Look Good on Paper" (Visual Basic Programmers Journal, July 99), he covers the basics of getting lines, curves, and text onto a form and out to the printer. Eureka! All the pieces just fell into place.