[GreenKeys] HRS312 TTY Interface

[Jon Schlegel]

Hi All,

I've been thinking of adding a series diode-resistor network across 
the mags to dissipate their turn off current and adjusting the 
resistor value to, in effect lengthen the turn off delay of the MOS 
switch to match it's turn on delay.  The correct resistor value might 
be determined by adjusting it for greatest range setting during RY test.

ADDITIONAL ASSET:  Probably one of the best ways going to quench the 
inductive kick.

LIABILITIES:  Diode-resistor network most likely must be wired 
directly across the mags, within the machine itself.  Most likely 
cannot integrate the network into a standalone keyer package (diode 
would be forward biased when keying switch is "off"...).

This all leads to an interesting question.  Does the mechanical 
adjustment of the selector mechanism take into account any specific 
current profile in the magnets?  generally speaking, the expected 
profile would be a relatively slow current build up during 
space-to-mark transition followed by a faster current drop during the 
mark-to-space transition.

Also, are issues like this why a "holding" magnet selector is, I 
think, considered better than a "pulling" magnet selector?


If anyone know this kind of info it could have a bearing in the 
diode-resistor idea I described.

Regards,
Jon Schlegel WA3MVM


At 12:59 PM 3/10/2009 -0800, David Ross wrote:
>The HSR312 is a simple & convenient device to use, but it introduces
>significant distortion.  The HSR312's turn-on time is specified at 3.0
>millisecond max and it's turn-off time is specified at .5 millisecond max.
>
>This is probably negligible if one uses the HSR312 between a PC and a
>teleprinter, but if you are dealing with off-the-air signals then the
>distortion may become objectionable.
>
>Dave Ross    N7EPI
>
>
>
>Duncan M. Brown wrote:
> > Then last month someone mentioned the HRS312 MOSFET optocoupler and that
> > looked like the heart of a very simple interface.  Jon Schlegel and I have
> > been playing with the HRS312 and  it seemed like the circuit was so simple
> > that it could be placed inside the 9-pin D-connector's housing.  I found I
> > had some AMP 745854-3 housings. There is room for a 5/8" x 3/4" board,
> > which is plenty big enough (point-to-point wiring).
> >
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