Resent! Lost in cyberspace?? Lost in spam filters??
Hi Arachnoids,
I did some experiments doing measurements using the ports.
First try was the game port on my other computer but I was not able to
activate that port. That game port is a part of the Sound Blaster card
with a PCI-slot and I was never able to activate the SB card under DOS.
Second try was RS232 port on the same computer as on the one I am using
right now.
The goal was to do either a measurement of a resistance or a capacitance
by loading a capacitor via a resistor.
A capacitor is connected between ground and CTS-line... the CTS-line is
used for the detection of the capacitor reaches the loaded state.
Loading is done via a resistor by making the RTS output line high.
The time that is needed to load the capacitor is clocked by a program
loop in the computer. (Tested on 75MHz and 100MHz Pentium I)
For capacitance measurements this is simple and effective but the values
to be measured are restricted to over 1 micro-farad. Accuracy abt 5%.
Resistance measurements can be done but... the results are non-linear at
all and restricted to values below abt. 10 kilo-ohms.
However watertemperatures can be measured in this way using an
NTC-resistor of say 2.5 kilo-ohm (at 25 centigrade).
A calibration list could be part of the computer program.
All programming has been done in QBASIC (DOS based).
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A big improvement was realized by adding a 555 timer IC. This makes
things a bit more complicated but still low tech.
Capacity and resistance are now linear and an accuracy of 1% is
possible.
Range: 200pF steps or 20 nano-farad steps up to 1 Farad (capacity)
150 Ohms to 1.5 Mega-Ohms for resistance
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It seems that programming in Pascal or C will give a better definition;
BASIC is rather slow for the counter loop... but I do not manage the
fine art of Pascal or C programming.
Anyone interested? It will take about a week to make a documented paper.
Regards, Bastiaan
