🚀 go-pugleaf

hort@hollywood.ems.cdc.com (Mark Hortman) writes:

>There is going to be a fair this weekend where I could by a cheap Oscilloscope.
>I was thinking it might be as easy to use my PC and it's gameport as a
>A/D converter and use it as an O-Scope.  

>Anyone done this for 5 or 12 volts?
>Seen any free/share ware to help?

The game port on a PC is not an A/D converter.  A write to the port sends
a voltage through an RC network - the resistor is in the joystick ( or
what ever ) and the capacitor is in the machine.  After you write to the
port, you have to poll the port and wait for the capacitor to discharge.
This is represented by one of the bits read from the port.  So, since it
takes a varying amount of time to convert each value, you would have to
write software that will compensate for the time differences.  Yuck.

You might try using your printer port (parallel port) for input.  Most clones
will allow you to read data in on the data lines of the printer cable.  This
way a sample will only take one instruction ( the game port would take many!).
Of course this requires that you have external circuitry like a pre-amp and
and A/D converter.

If you want the screen to 'scroll' the wave form, the software will be tricky.
Unless you are doing very low frequency stuff, you will surely have to do the
screen updates (scrolling) in assembly language.

Most commercial solutions require a hardware/software purchase.  I don't 
know of any free/share solution.

If you find a cheap scope, buy it.  You'll need it when your computer breaks!
A dual channel 20Mhz scope can be bought new for $350 - $450.  I would 
consider $200 a good deal on a working used scope.

Hope this helps.


-- 
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*	Bill Quinn			billq@ms.uky.edu		*
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