Re: How do I control soft switches?

[chm114u@vaxc.cc.monash.edu.au]

In article <1eamgvINNgks@gap.caltech.edu>, toddpw@cco.caltech.edu (Todd P. Whitesel) writes:
> hiroki@limerick.cbs.umn.edu (Hiroki Morizono) writes:
>
>>Hi, I'm trying to open/close a switch using  a solid state relay, from
>>the game port of an apple2e, using game controller 0
>
> Bzzt. Game controller 0 is an input. The output your program correctly controls
> is "Announciator 0" or AN0 for short. This is -not- connected to the 9 pin

     < good stuff deleted)

> Also, make sure the relay can activate with only a few mA of current at about
> 3 volts, because that's all the TTL output can provide. I STRONGLY advise that
> you spend a little extra time working up a transistor switch or something
> similar; TTL outputs are _not_ designed to power things, and you may fry a
> chip on your motherboard if you draw too much current for too long.
>
> Todd Whitesel
> toddpw @ cco.caltech.edu

These days, I always use an optocoupler. They switch more nicely than a relay,
they're sensitive and they're inexpensive (about 50 cents Australian). Use a
couple of thousand ohm resistor to limit the annunciator current. They also
provide more protection from "nasties" from the load you might be switching.

Mike Atkinson  chm114u@vaxc.cc.monash.edu.au
               Chemistry Dept., Monash Uni., Melbourne, Australia.