Caple C871i Manual do Utilizador descarregar pdf (Página 98)

100

101

Apple II Computer Info

The existing LED circuit is:

560ohm Red LED

+12v switched ----/\/\/\/----B --|>|-- 2---Gnd current =

As a Red/Green LED can do 3 colours (Green, Orange and Red) but we cannot

do only Green or Red (as one LED will be run from the existing Enable while

the 2nd will illuminate when writing is also occurring), I would recommend

the following:

560ohm

+12v switched ----/\/\/\/----B --|>|---+ Green LED

Gnd--2 --------+

ULN2003 (D4-10) --/\/\/\/---------|>|---+ Red LED

180ohm

This way you get Green for reading and Orange for writing. This immediately

tells you that the drive has been modified and the contrast between green

and orange is higher than between red and orange.

I do not know if the write signal is actually long enough to see (formatting

a disk should be no problem but normal writes may not keep the red LED on

long enough to see). If this is the case, additional circuitry would be needed

to stretch the write pulse to the LED.

Note, this has not been tried, I make no guarantee that this will work.

Try it on scratch disks first.

To calculate LED currents, use the following formula:

Iled = (Vsupply - Vled) / R

so for the original circuit:

I = (12 - 2) / 560

= 10/560

= 17.86mA

The output of pin 10 of the ULN2003 is clamped to a maximum of 5 volts by

a diode so:

I = (5 - 2) / 180

= 3/180

= 16.67mA

David Wilson School of IT & CS, Uni of Wollongong, Australia [email protected]

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Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 98 of 572

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Caple C871i Manual do Utilizador Página 98

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