Re: A newly working Commodore 720 - many questions...

On 2/22/2012 1:42 PM, Gerrit Heitsch wrote:
> On 02/22/2012 07:57 PM, Jim Brain wrote:
>> On 2/16/2012 10:49 AM, Gerrit Heitsch wrote:
>>>
>>> D1 = 1N4148
>> Why is D1 needed? In the reverse mode, the optocouple won't conduct, so
>> they're no concerns.
>
> A LED can only take a very limited reverse voltage. The number I once 
> learned was 5V, apply more and you might destroy it. The antiparallel 
> 1N4148 limits the reverse voltage to 0.7V.

I thought they were well about 6V.  Makes sense.
>
> The idea with the cap was not to stretch the cycle but to filter out 
> short voltage spikes (line noise). The value was a guess back then, 
> but if you omit it, your clock will be fast (that part was tested).
That's my digital side peeking out.  Never thought about line noise on 
the TTL.

JIm


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