User`s guide

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From: Paul Guertin
001- Could anyone suggest a good project book for the
Apple IIe. I'm interested in using an old box for
tracking the temperature in a water bath.
Vernier software publishes a book called "How to Build a Better Mousetrap" which
contains 14 hardware projects for the Apple II. Project #6 is a temperature
probe connected to PDL0.
ISBN for the book is 0-918731-16-X.
Vernier Software ( http://www.vernier.com )
2920 S.W. 89th Street
Portland, Oregon 97225 USA
[phone]
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From: Sheldon Simms
A good book is _Inside The Apple IIe_ by Gary B. Little. It isn't a project
book, but it does have a good chapter on using the Game I/O connector for
"electronics experiments."
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From: Cyrus Roton
002- How can I use a thermistor (a resistor which has a
variable resistance related to ambient temperature) to
read temperature on my Apple II?
You can connect a thermistor to a paddle input and supply a voltage to the other
end. Current flows through the thermistor to charge a .022 mfd capacitor inside
the apple2. When the paddle is read, the apple2 discharges the capacitor and
resets a timmer. Then the cap is allowed to charge. When the charge reaches the
trigger level (3.2 volts) the timmer is stopped and the count is read out.
The lower the value of the thermistor, the faster the charge and the lower the
count. Also, the higher the voltage, the faster the charge. A resistance of
about 120K with a 5 Volt supply will give a count of about 250. You can add an
external capacitor across the paddle input (to ground) to increase the charging
time (if needed)
The formula is charge=input volts * (1 - exp(-t/RC))
So, you can use a supply voltage and external capitor as required to fit the
resistance value of the thermister (or other resistive component). Probably, the
best way to find the correct values woud be to try a variety of values and plot