RE: Please help with Catweasel Reed-Contact

From: Baltissen, GJPAA (Ruud) (
Date: 2005-08-18 14:22:24

Hallo Antitrack

> Very well, but how would a digital line like this replace a 
> phototransistor like in the original unmodified PC drive?

Because that phototransistor is used in exact the same way: as soon it is
lit, it pulls a line low that originally was held high to +5V through a
resistor. The way how it is used makes the circuit digital, not the fact
that a transistor can behave analogue. Just take 1541 and have a look at the
write-protect sensor of it. 

FYI: although you'll see only two connections, it is still a transistor.
Normally feeding the Base connection with current will make the transistor
conduct current. But in this case light is the trigger and therefor the Base
connection is not needed.

With a bit of luck you can replace the phototransistor with an Hall-element.

What I forgot to mention is that the Hall-element of the 3.5" drive I
mentioned, is found near the disk motor.

Just comes to my mind: why do you want to use a magnet again? I am the last
one to let a magnet near my floppies!

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