🚀 go-pugleaf

phr@telebit.com (Paul Rubin) writes:

>I am interested in a cheap way to monitor some slowly changing
>voltages (read: DC) in a piece of test equipment.  8-bit resolution
>is fine.  I can scale the voltages to the 0-1 VDC range (or similar)
>using resistor networks if I need to.

I'd worry about common mode/ ground loop problems if you are using
any PC port as an A to D without some sort of DC isolation.

What I'd do is get a serial A to D convertor such as the Texas 
Instruments ADC831 or TLC549, probably the latter since its CMOS.

To interface to this you need two outputs from your PC and one
input.  I have used a printer port for projects like this.
With only three signals, you can power the ADC circuit from a battery,
avoiding grounding problem, and use opto-isolators to connect
to the PC.

Then to drive the software, you activate the CS chipselect to start
the conversion.  then pulse the I/O CLOCK line, sampling the input
to collect the serial bits.

It should be way cheaper than $79 if your time to build and program
is 'free'
 
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