[Mldxcc] Keyer Finished (was Re: 2n2222 vs 4401? Opinions?)

[Emileigh Starbrook]

Oh..... I would have preferred an optoisolater for a number of reasons
(drain on the USB port power supply for one) but unfortunately Radio Shack
doesn't have them any longer.  which is very unfortunate.

In the end I opted for what I had, which was two 2N3904 transistors. The
second needed to reverse the on-off of the first which somehow was
backward.  Not sure if that is how MixW handles the DTR line but I suspect
it's just what the USB to Serial chip maker did.  In the end I had to add a
2.2K pullup between the collector of the first 3904 and the base of the
second so it would fully shut off but it works great.

If anyone is interested in building one, here is the link to the USB to
Serial module I used.

http://tinyurl.com/lh7cwna

It and the small perf board with the transisters and resisters on it fit
into this small (2 AA batteriy holder) enclosed case from Radio Shack:

http://tinyurl.com/k58kc6j

I had to modify it by dremelling out the center divider but that took two
minutes.

Cheers,

Emi

------------

I couldn't wait for success, so I went ahead without it.
- Jonathan Winters

On Sun, Nov 2, 2014 at 8:58 PM, w6de <w6de at tealpond.com> wrote:

> I built my computer keying interface with an optical isolator, which would
> be
> slower switching than either of those two transistors.  Sometimes slower is
> better, in that the slower switching rates do not create higher frequency
> artifacts that you have to deal with.  In addition, sometimes they are less
> susceptible to induced interference, e.g. RF feedback (RFI susceptibility).
>
> For a keying circuit I'd select the device with the lower frequency gain
> (lower
> Hfe).
>
> Dave, w6de
>
> -----Original Message-----
> From: Mldxcc [mailto:mldxcc-bounces at contesting.com] On Behalf Of Emily
> Clarke
> Sent: Sunday, November 02, 2014 04:43
> To: Mldxcc at contesting.com
> Subject: [Mldxcc] 2n2222 vs 4401? Opinions?
>
> I want to build a keyer from my computer, and I think having the key
> avalanche
> fast to ground is more desirable than slow when building it.
> I have both transistors and while I would have preferred to use a
> darlington
> optoisolator, I couldn't get one.
>
> So - going the transistor approach - which is better?  a 2222 or 4401?
> I know they can all handle the switching but is there any advantage?
>
> I'm using an Icom 746 - and I assume the keyer only wants to see ground.
>
> thanks in advance,
>
> Emi
>
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