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

From: Gerrit Heitsch <>
Date: Wed, 22 Feb 2012 20:42:36 +0100
Message-ID: <>
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.

>> C1 = 10 nF
> I assume it's there to stretch the cycle. Given the 6.3V transformer
> will have enough forward voltage for most of the half cycle, is the cap
> really even needed?

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).


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Received on 2012-02-22 20:00:26

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