Cassette Interface Assistance

[Seth Morabito]

* On Tue, Feb 28, 2017 at 09:55:30AM -0600, Jim Brain via cctalk <cctalk at classiccmp.org> wrote:
> Analog, which is my nemesis, curses me again.
> 
> I have a cute idea for a cassette port project for the Tandy line of
> computers (the ones with the cassette port).  I have a Coco 3 on the bench,
> so I scoped the output line while doing 'csave "jim"'.  The signal looks to
> be just under 1V PtP (0-1V on the scope), and rests at about .3V when not
> sending data.
> 
> I have tried 6 different ways to boost the signal to 5V digital, to no
> avail, and so I ask humbly if someone with analog knowledge might be able to
> assist.

Hi Jim,

When I was building a cassette circuit for my homebrew 6502 computer,
I essentially stole the Synertek SYM-1 circuit wholesale. See:

http://www.loomcom.com/blog/2013/01/04/retrochallenge-update-comparator-vs-zero-crossing-detector/

http://www.loomcom.com/blog/2013/01/05/comparator-success/

Synertek used an LM311 (an LM358 would work just fine) to build a
comparator circuit. I _think_ you could use this exact circuit to
take the analog output from the CoCo and turn it into a 5V sqauare
wave.

-Seth