Re: How do I control soft switches?

[toddpw@cco.caltech.edu (Todd P. Whitesel)]

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
D connector you've been testing; it's only available on the 16-pin DIP plug
inside the computer.

>So before doing anything, I decided to just put wires in pins 5 and 3,
>Game control 0, and ground , and hook em up to a multitester. Got no changes 

This is because the changes your program was making didn't show up here. Try
popping the top off and testing pin 15 of the DIP plug.

>Am I right in assuming that once TTL is set high, it stays high, or do I 

Yes. Be careful though, a reset will force it to some state (I forget which),
and some applications like to mess with it because they think something else
is plugged in there.

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