Re: Tek 576 Curve Tracer USB port to a cpu ... ?


 

Hi Ke-Fong Lin,

Digitizing the deflection voltages is a great idea because of its simplicity. It would be easy to capture the deflection voltage for both axes with A/D converters and convert it into X-Y data. A few issues that may make it a bit more difficult:
* The deflection signals are differential so the X axis would require two A/Ds sampling the two vertical deflection plates and two A/Ds sampling the two horizontal plates. Both of the vertical A/Ds would need to sample simultaneously. The same is true for the two horizontal A/Ds.
* There is no information about what you are looking at. For a simple example of measuring a bipolar transistor the data you capture has no information about the Volts/Div of the horizontal axis or the Amps/Div of the vertical axis, or what current step caused the trace to move vertically and by how much.
* You have no idea when to start and stop capturing the data. This might be easy to fix if there is a start sync pulse you could use to trigger the A/Ds. I'm not aware that there is a Stop pulse. It may be possible to use a Z-axis output signal or un-blanking signal, if one is available somewhere inside the curve tracer for this. The A/Ds would start when the un-blanking signal went true and they wouldn't stop until the un-blanking signal went false.

Assuming there is a way to use the un-blanking signal or equivalent this might work.

The way this could work is by pressing a momentary push button to tell your software to take a sample of the next set of curves. It would then wait for the un-blanking signal to go true. The software would automatically write the data streaming from the four A/Ds to local memory. When the un-blanking goes false, indicating the curve tracer is done displaying a complete set of curves the A/Ds would be stopped and the software would automatically send the sampled data to a display or back to the curve tracer's CRT so the user could decide if they wanted to save it permanently or do this over again. If you decide to save the data it would then ask you to enter the settings of the curve tracer knobs or maybe what would be better would be that you have the software generate a pattern on the CRt that could be as simple as a diagonal line for example. By adjusting the line so it starts in the lower left corner of the screen and ends in the upper right corner of the screen you are providing a calibrated range that can then be used by entering the settings of the vertical A/Div knob and the horizontal V/Div knob. Finally you would include the base current steps and how many steps there were.

This actually might work!!!

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Ke-Fong Lin
Sent: Wednesday, January 08, 2020 2:00 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 576 Curve Tracer USB port to a cpu ... ?

Would it not be a simple matter to somehow convert the 576 deflection
plate voltage signals to X-Y Data? Just thinking out loud here.
As mentioned already, the refresh is at 60Hz so a pen plotter cannot go that fast.
However. it should be possible to have the display "static" and have the plotter slowly do it's work.
But then you would have to design a mechanism to "follow" the "beam" at the slow pen rate.
That would be quite complicated.

In contrast, the spectrum analyzer is a single f(x) function to plot.
And in the case of my HP3580A which is a low frequency SA, the sweeping speed is very slow (can be a few minutes).

Indeed, what looks easy for an Arduino, may not have been in the 70s!







--
Dennis Tillman W7PF
TekScopes Moderator

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