Re: [CAD_CAM_EDM_DRO] Re: ParPort output low - hi-Z or ground?

On Thu, 08 Apr 2004 18:17:44 -0000, you wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ghidera2000"
><ghidera2000@y...> wrote:
>> Spent a day drawing up an optoisolation scheme for the parallel
>> port. I know the inputs go between +5V and 0V but, when you set an
>> output to low, is it connected to ground or does it go hi-Z?
>>
>> Silly me, I was thinking in terms of sourcing current from the port
>> (OUTput...) and getting fancy with transistors. Just as I finished
>> the drawing (As usual!) I realized that its TTL and TTL is much
>> better at sinking. If it goes to ground then a couple resistors and
>> 1N4148's are all I need to drive the opto-leds.
>
>Hi,
>I'm also working on a a3977 board, after a week of work I've decided
>that having a 6n136( 4n25 won't do it,it need a lot of current going
>thru it on the input to have a good CTR) opto conected to the
>parallel port thru a 1k resistor,(led side of the coupler) and a 7404
>i.c on the output side of the 6n137 to bring the signal to be in fase
>with the input signal is the best way(I think).

I'd recommend a 74LS14 instead. Lower loading, and schmitt trigger.
Gives you better transitioning on the rather slow slope from an opto
isolator.

Harvey

> there is no electric connection in bettwen one side of the opto and
>the other, so if anything goes wrong with the drive it will have no
>efect on the parallel port.
> I also have added a current reduction circuit based on the 555 i.c
>If you're using a 4n25 opto type you need to supply 5v to it on the
>input side.
> the 6n136 has a very good transfer ratio so as litlle as 1.2UA is
>enough to get it going on the other side.
>tested the board today, and it works very well, up to the computer
>limits(40Khz)step pulse.
>
>Good luck
>Fogassa
>
>
>
>
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