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From: ford@crash.CTS.COM (Michael Ditto)
Newsgroups: comp.sys.amiga
Subject: Re: Converting an Atari Trackball to an Amiga Joymouse
Message-ID: <1328@crash.CTS.COM>
Date: Fri, 3-Jul-87 08:56:31 EDT
Article-I.D.: crash.1328
Posted: Fri Jul  3 08:56:31 1987
Date-Received: Sat, 4-Jul-87 17:14:46 EDT
References: <595@madvax.UUCP>
Reply-To: ford@crash.CTS.COM (Michael Ditto)
Organization: Crash TS, El Cajon, CA
Lines: 54
Keywords: Hardware schematics
Summary: No external logic required!

There is an Atari trackball which is commonly available in toy stores (I just
bought one for $8.95).  It has a normal optical shaft-encoder type mechanism
producing quadrature signals, and a circuit to convert this into direction/
step signals which are output to the connector.  A while back, someone posted
a circuit that would convert this back into the quadrature signals the Amiga
likes, but I just tapped in to the original signals.  Here's a basic
description:

	The trackball I have has a brown plastic top half and a beige plastic
	bottom half, a yellowish que-ball sized ball, and two buttons which
	are connected to each other (i.e. the same pin on the connector). It
	has a sticker that says "ATARI TRAK-BALL" just below the ball. It
	also has a "Joystick  -- Trackball" switch on the side.

	Inside the cabinet, the cable plugs into the circuit board with a 6-
	pin connector, with a seventh wire going straight to one of the two
	buttons.  The six wires are black, orange, blue, white, brown, and
	green.  I removed the wires from the connector and soldered them to
	the circuit board as follows:

	Black:		pin 1 of 6-pin connector (same pin it used to be on)
 	Orange:		pin 2 of 6-pin connector (same pin it used to be on)
	Blue:		hole labeled "TP2" on printed circuit
	White:		hole labeled "TP3" on printed circuit
	Brown:		hole labeled "TP1" on printed circuit
	Green:		hole labeled "TP4" on printed circuit

	Leave the red wire connected to the buttons as before.

	This configuration allows the trackball to be used as a mouse;
	rolling it away from you moves the mouse pointer upward on the
	screen, etc.  For some reason, Marble Madness does not expect this
	and you have to use the "mouse" setting.  I don't know if there is
	any difference between the trackball and mouse settings anyway,
	other than the fact that their trackball setting is "upside down"
	from the mouse setting.

	Note that this does not address the problem of having both buttons
	connected to only one button input.  Another wire alongside the
	main one, or a replacement cable would take care of this.
	Unfortunately, I don't remember which pin (TP1, etc.) is which
	quadrature  signal or Amiga connector pin number, but you can figure
	it out with a continuity tester and the original cable, using my
	connection description above.

That's it!  It actually is just bypassing the extra level of convertion that
was already in the trackball.  So dig out the old Marble Madness disk and
have fun!!  And play around with workbench with a trackball; you might like
it better than a mouse, but you won't get far without a menu button.
-- 

Michael "Ford" Ditto				-=] Ford [=-
P.O. Box 1721					ford@crash.CTS.COM
Bonita, CA 92002				ford%oz@prep.mit.ai.edu