Cassette Interface Assistance

[Jim Brain]

On 2/28/2017 11:42 AM, Seth Morabito via cctalk wrote:
>
> 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.
I will give it a try.  Obviously, I'll need to reset the bias down to 
.5V from 2.5V in your design, but I can do that.  I notice the design 
has no feedback, but has R93 feeding the reference into the inverting 
input.  Any idea what the function of that resistor is?

Jim