[GreenKeys] Model 19 on ITTY

[ad7i]

Al --

If you has some source of audio from ITTY (or any AFSK generator) and
simply want to convert that AFSK to a logic level output, you are likely
able to take advantage of the high signal to noise ratio of that signal (no
noise) and use a one-shot timer arrangement to decode the AFSK.  Run the
audio through a single op-amp limiter, to convert the sine wave AFSK into
square waves, then use a timer (555) to look at the time between zero
crossings of the limited audio signal.  If it's less than X the logic
output is zero, if it's more than X the logic output is 1.  But be sure to
time between same polarity zero crossings (time between rising crossings or
falling crossings) as it's very difficult to be a 50% duty cycle signal out
of a limiter.

Note that this ONLY works when there is NO NOISE on the AFSK signal.

Paul, ad7i




On Fri, Jan 24, 2020 at 9:58 AM Al Klase <ark at ar88.net> wrote:

> Hi Ralph, *et al*
>
> The point is we don't have a TU.  We'll be running a PC anyway if we
> monitor ITTY.  Logic level to current loop isn't a problem, and I've found
> an Arduino "sketch" that will go from ASCII to baudot.
>
> I'm exploring RTTYT which looks like it will handle the PC chore.  The
> scheme is complicated by the fact that modern PC's don't have RS-232 ports,
> and the UART's in the USB dongles don't support 5-bit formats.
>
> 73,
> Al
>
> On 1/23/2020 5:00 PM, Ralph Mowery wrote:
>
> Doesn’t the audio come out of your computer speakers ?   If so you could
> just run that audio into any modem/TU and then to the machine.  I think
> that is what I did a year or so back.
>
>
>
> Ralph ku4pt
>
>
>
>
>
>
>
> *From:* greenkeys-bounces at mailman.qth.net [
> mailto:greenkeys-bounces at mailman.qth.net
> <greenkeys-bounces at mailman.qth.net>] *On Behalf Of *Al Klase
> *Sent:* Thursday, January 23, 2020 4:40 PM
> *To:* greenkeys at mailman.qth.net
> *Subject:* [GreenKeys] Model 19 on ITTY
>
>
>
> Gang,
>
> We're still klutzing around with TTY's at the Radio Technology Museum, and
> we're starting to make some progress.  So, how do we get data from ITTY out
> to the machine?
>
> I have MMTTY copying the stream FB, but don't see the hooks to get the
> data out.  Even 8-bit ASCII on a COM Port would be OK, as we can use
> TinyFSK on an Arduino to get to Baudot.
>
> I may just be dense. :-(
>
> Al
>
>
>
>
> --
> Al Klase – N3FRQ
> Jersey City, NJhttp://www.skywaves.ar88.net/
>
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