Re: ][e paddle port annunciators...

[Dennis Jenkins <dennis@usb.com>]

Dave Althoff Jr wrote:
> 
> For Christmas, my brother gave me a neat toy...a KNex Ferris wheel kit.
> Nice.  But the drive system on it is absolutely horrible.  It comes with a
> little 3v geared motor with a battery box containing two AAA-size
> batteries and a switch.  Trouble is, the motor has a worm gear, so it
> can't slip, and the wheel has no clutch on it.  Lousy engineering.
> 
> But then, I have these ][e's lying about.  It seems to me that with a
> simple bit of machine code, I could turn the paddle port into a neat
> little DC motor controller, using the annunciator instead of the battery
> box to power the wheel.
> 
> So the question is...How much current can I draw off of the annunciator??
> Not being much of an electronics geek, but knowing that the motor won't
> complain at being fed 5v instead of 3v...any advice for protecting the
> computer?
> 

I did something like this in 1993 in high school.  I took AN0 into a
2n2222 transistor, which switched a larger power transistor, which drove
the motor.  It ran like crap, probably b/c I used spare parts instead of
getting a real power transistor.  The power transistor required a large
heat sink though.  If you have access to decent specs, you could
probably get the correct components.

You may also consider using a device called an "opto-isolator".  I seem
to remember that they can drive sufficient current to power a small DC
motor.  Lacking that, have AN0(,1,2,3) drive a small transistor which
drives a small relay.


obhack:
	The IIe I used in high school lacked a clock card, and I wanted to do
some precise timing.  So I wrote some assembly code that counted the
VBLANK single ($c021?) and derived it's timing base from that.  I used
some calculations to pulse to motor and was able to control the motor's
speed using PCM.

-- 
dennis@usb.com                           Universal Savings Bank.

The three most dangerous things are a programmer with a soldering
iron, a manager who codes, and a user who gets ideas.