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/j...l#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/