Nuts and Volts - June 2015

analog channels. I created the plot using the built-in Excel functions so that any data written into the columns D, E, and F would be plotted in real time as it came in, using column B — the time — as the X axis.

A Little Finesse — Making Life Easier

It really took me less than five minutes after opening PLX-DAQ for the first time before I had data in Excel and plotted. Now, I was ready to add a few simple features to clean up the data.

PLX-DAQ understands a few code words. The word DATA in front of each line of data (separated by commas) is the command to place each data value in a separate cell on the same row.

The line feed Serial.println(), as the last line in the serial.print statements, also prints the line feed and tells PLX-DAQ to add the next set of data to a new row.

There are two other commands I find very useful. The first is CLEARDATA. When this key word is printed to the serial port, PLX-DAQ will clear the cells in the Excel spreadsheet and move its pointer to start adding data to row 1 in the first worksheet. This means I can use the same worksheet over and over again — especially if I have a graph already formatted the way I want.

When I have a set of data collected and I want to keep it, I make a copy of it and place the copy in the first sheet position. This is done with a right mouse click on the worksheet tab and selecting the copy command.

Now, I have a new worksheet ready to collect and plot data with formatted plots, but it’s full of old data. When the CLEARDATA command is sent, the old data in this new spreadsheet is cleared out and I start over with a blank worksheet. Fortunately, a plot is already formatted, waiting for new data to plot.

The second command that makes my life easier is LABEL. I like to have my data as well documented as possible. In this simple example, I wanted to display five columns of data, the number of points averaged per data value, the real time each data point was taken, and the three analog values from each channel. I used the LABEL command to send the labels for each column (separated by commas) as the first command.

This command only needs to be sent once, to set up the column labels. I put this in the void setup() function, so it executes right at the beginning of the sketch. Since I wanted a little flexibility on how I use the serial port, I added the flag to only print the LABEL command and values if the PLX_flag is set for true. These commands are

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Avoid this common problem: While the standard baud rate for the serial port is 57600, PLX-DAQ only offers the option for

56000. If you use 57600, some of the data read by PLX-DAQ will be garbled. You must set up the baud rate in the Arduino sketch with the same value as you select in PLX-DAQ. I recommend the highest value of 56000 as your default.

Avoid this common problem: Only one device can use the serial port at a time. The most common mistake I make is having the serial monitor open to read the serial port while I want to have PLX-DAQ read the data. I get an error in this case. Wait for the code to be uploaded to the Arduino and be running. Make sure nothing else is talking over the same COM port, and then click the “connect” button.

Likewise, to talk to the Arduino, be sure to click the “disconnect” button on the PLX-DAQ dialog box to free up the serial port connection for the Arduino.