XYdisp: A program to use your old PC as XY display.
I wrote this program to use an old 486 type laptop as an XY display. My main purpose was to display the response of a filter, amplifier etc. when using my signal-generator as a sweeper (or wobbler as I also called it) and microwattmeter as detector. I used to do this with a oscilloscope which had a long persistence display but considered that using a PC program offered the advantage of being able to make screen-dumps for documentation purposes.

XYdisp measures just the X- and Y-voltage output by your measurement setup. It does not communicate with or has any knowledge of what instruments you connect. It is therefore a simple display program you could easily adapt to your own needs without having to modify your equipment other than perhaps converting output voltages to be between 0 and 5V.

XYdisp runs on any PC from an old 386 to a modern Pentium. It runs under DOS and uses the PC's parallel port, so it will not run under NT or XP. It uses a simple parallel-port one-chip I2C interface. On the I2C bus is a Philips PCF9851 ADC/DAC chip. This has a four-channel 8-bit ADC and one 8-bit DAC. I use only the first two ADC channels in the program.

The first channel measures the X-signal or horizontal voltage, which is generated in my signal-generator.
The second channel measures the log-detector's response, in my case the log-output voltage of my microwattmeter.

XYdisp is particularly suited for sweepers with a triangle-shaped sweep-voltage as there is no problem with the 'back-trace' (?) as with a sawtooth shaped sweep-voltage. However, you could modify XYdisp to use a third channel to monitor a 'back-trace' signal to suppress this in the display.

The result of XYdisp may look like this:

Here is a zip-file which contains the program executable, the program source and a user-manual with schematics.

Send your comments (email address is on my home-page)