Caple C871i Bedienungsanleitung PDF herunterladen (Seite 500)

Apple II Computer Info

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### FILE : thermistor

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### Created : Friday, September 27, 1996 Modified: Friday, September 27, 1996

### File Type: "TEXT" File Creator: "LMAN"

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From: Cyrus Roton <[email protected]>

Subject: Re: read temperature from i/o port

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Date: Wed, 6 Mar 1996 16:37:55 GMT

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On 5 Mar 1996, Dave Althoff wrote:

> A thermistor is a reisitor which has a variable resistance related to

> ambient temperature. I've seen them at Radio Shack in the parts cards,

> and those indicate what the resistance is at a particular temperature.

> The paddle ports on an Apple ][ are 150k ohm (or was it 150 ohm...I don't

> recall off-hand). So that is the range of resistances you need to work

> with. -------------- snip -----------------

You can connect a resistor to a paddle input and supply a voltage to the

other end. Current flows through the resistor 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 resistor, 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

Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 500 of 572

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