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In article <29928@nntp_server.ems.cdc.com> 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?

On the use of the PC game port, see an article called "Joystick Metrics"
that I wrote for _PC Tech Journal_ around 1985.  

The sampling speed is _very slow_ for oscilloscope purposes, but if you are
dealing with slow things (like 1 Hz) it's just what you need.

-- 
:- Michael A. Covington     internet mcovingt@uga.cc.uga.edu 
:- Artificial Intelligence Programs       phone 706 542-0359
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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.


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

In article <29928@nntp_server.ems.cdc.com>, 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 (IBM) PC's game port isn't truly an A/D converter. It merely measures the
timeconstant of the RC circuit formed by the joystick and an on-board
capacitance. Short of using a similar technique (with a lousy b/width), the game
port won't let you measure analogue signal levels.

You could make a PC oscilloscope if you were prepared to purchase a third party
add-in ADC card for your PC.

John Haddy

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    |_| (_) | | | |  | | (_| (_| (_| \/           School of MPCE
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    Email: johnh@mpce.mq.edu.au, Ph: +61 2 805 8959, Fax: +61 2 805 8983

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

I have available a 500+line file of C-code and  schematic for a 6-transistor
Analog-Digital converter, that on my 12?MHz AT will perform 15,000+
acquisitions per second. Yep....successive approximation. And dirt cheap
R-2R-4R-8R....DAC, and really crappy one-transistor comparator. You can use
Turbo-C to paint samples onto your PC screen, as "realtime" scope.
Works through your Parallel Printer Port. SEND ME MAIL if you want the file.

Of more interest is my second pass at a CHEAP 500 picosecond risetime 
sampling scope. It will need A REPETITIVE SIGNAL. Design not finished yet,
but uses 6 ICs, giving one channel. Probably 9 ICs for 2 channels. 
Allen Sullivan  Enjoying Tek556 scope (85 pounds), & HP852A SpecAnalyz (100+)