Newsgroups: alt.electronics,sci.electronics,sci.electronics.misc
Subject: Re: Suggestions for PC Oscilloscope
References: <[email protected]>   
kony  writes:

> On Wed, 24 Sep 2003 09:47:58 +0100, "Geoff Hackett"
>  wrote:
> 
> >Hi,
> >
> >Some older non PC computers have A/D built into joystick ports or sound
> >capture ports. The Acorn BBC and Amiga computers I think. You could look at
> >getting an old one cheap. They can be programmed in basic for the graphics
> >etc.
> >
> >Or just buy a used audio scope. 10Mhz 1 Channel.
> >
> >Geoff
> 
> 
> It's not just older, non PC computers, the typical "standard" joystick
> port found on most if not all PCs is analog, then A/D converted.
> However the range might be poor enough to make the resulting readings
> too inaccurate?  

The resulted treading from the PC joystick port is quite inaccurate.
The A/D converter system used in PC joystick hardware is very 
simple. It is basically a one-shot multivibrator that is 
triggered by software, and then software loop counts the pulse 
length. This system is not particularly accurate (variation 
between different ports, between differenc changes, PC temperture 
has it's effects), the software measurin has it's limits 
(in practice less than 8 bits of resolution) and the measuring
is slow for most oscilloscope applications (conversion time 
can be up to 2 milliseconds, typically around 1 ms, so 
sample rate can't be higher than 1 kHz, usually less than this).

You can find circuit to convert voltage to signal that can be connected
to PC joystick port input with the plans presented at
http://www.epanorama.net/documents/joystick/pc_circuits.html#generalinput


> Here's an application to do it with the sound "card"
> analog audio input instead:
> 
> http://polly.phys.msu.su/~zeld/oscill.html

This is a worth to check option if the soundcard performance 
is enough (limited only to AC measurements at audio frequencies).


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/