[GreenKeys] ASCII/RS-232/AFSK Interface for the Model 15 Teletype

Tue Jun 28 16:40:30 EDT 2022

So many people here are obviously EE ,MSEE , or Phd  graduates.
Advanced digital circuit design. I want you to know you are sending me back
to my textbooks.
Love the posts.
Oh…Irv Hoff was a friend of mine however, we both lived in same town.

 73 WA8OLD

On Tue, Jun 28, 2022 at 15:22 Mike Douglas via GreenKeys <
greenkeys at mailman.qth.net> wrote:

> Eugene,
>
> The selector magnet is energized/de-energized through T2 and RA5 You'll
> see the baudot data at RA5.
>
> RC2 through U1 is used to block or dump the charge that has accumulated on
> C1/C2 into the loop circuit.
>
> RC1 through T1 is used to add additional charge to C1/C2 during a space
> condition and after current from the selector magnet has decayed to zero.
>
> First, consider the idle marking state: RA5 is high, T2 is on, and 60ma
> flows from the 15vdc power supply through the selector magnet. At this
> point, RC2 is high so that the U1 is "off" and C1/C2 are isolated from the
> power rail.
>
> Now transition from mark to space: RA5 goes low so T2 turns off. The
> decaying magnetic field of the selector magnet dumps its energy as charge
> onto C1/C2 through D3. When that current flow reaches zero, D3 blocks the
> reverse flow of current out of C1/C2, so these capacitors hold their
> charge. Typical voltage reached on C1/C2 with a pulling magnet selector is
> 40v-60v on the mark to space transition.
>
> After the selector magnet current reaches zero, the processor runs the
> boost switching supply formed with T1, L1, D2 and C1/C2 to further boost
> the voltage on C1/C2 (if enabled).
>
> Next, the processor turns on U1 via RC2 to connect the voltage on C1/C2 to
> the power rail. D1 blocks the high voltage from reaching the 15vdc supply.
> At this point, everything is ready for the next space to mark transition.
>
> At the space to mark transition, RA5 goes high to turn on T2. Current
> flows from C1/C2 through the selector magnet until they have discharged
> down to the 15vdc supply voltage. Once this point is reached, U1 is turned
> back off via RC2 and we're back to the idle marking state.
>
>
> Mike
>
>
> On Tuesday, June 28, 2022, 12:42:06 PM CST, W2HX <w2hx at w2hx.com> wrote:
>
>
> Ok Mike. Just a question about the theory of operation of this circuit.
> From what I can surmise, RC2 on the U2 seems to be doing the signaling for
> the selector magnets. Meaning, I would expect the baudot code to be present
> on RC2 (am I correct?) can you elaborate on the functions and interplay of
> RC1 and RA5? All three seem to be involved in this output circuit.
>
> I think others would also be interested in the theory here. thanks
>
> 73 Eugene W2HX
> Subscribe to my Youtube Channel:
> https://www.youtube.com/c/w2hx-channel/videos
>
>
>
> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net>
> On Behalf Of Mike Douglas via GreenKeys
> Sent: Sunday, June 26, 2022 5:44 PM
> To: Greenkeys <greenkeys at mailman.qth.net>
> Subject: Re: [GreenKeys] ASCII/RS-232/AFSK Interface for the Model 15
> Teletype
>
> Eugene,
>
> Unfortunately, no, this board can’t easily be configured to work with an
> external loop supply.
>
> Mike
>
> > On Jun 26, 2022, at 12:06 PM, W2HX <w2hx at w2hx.com> wrote:
> >
> > What a great project! I have a question. Could the circuit be modified
> to only key an existing loop without the need for this board to generate
> the loop current itself? I would imagine maybe less components needing
> installation and some jumpers but I was wondering your opinion of that.
> >
> >
> > 73 Eugene W2HX
> > Subscribe to my Youtube Channel:
> > https://www.youtube.com/c/w2hx-channel/videos
> >
> > -----Original Message-----
> > From: greenkeys-bounces at mailman.qth.net
> > <greenkeys-bounces at mailman.qth.net> On Behalf Of Mike Douglas via
> > GreenKeys
> > Sent: Sunday, June 26, 2022 12:35 PM
> > To: GREENKEYS BULLETIN BOARD <greenkeys at mailman.qth.net>
> > Subject: [GreenKeys] ASCII/RS-232/AFSK Interface for the Model 15
> > Teletype
> >
> > I recently made a new version of the subject interface board that
> incorporates the changes I made to the prototype unit that you may have
> seen in a few videos I posted. I've made a web page to document this new
> version - see the link below. I still need to write a user manual and
> finish a small wish-list I've given myself for the firmware.
> >
> > https://deramp.com/model15_interface.html
> >
> > I have a number of bare PCBs of this new version if anyone wants one -
> just contact me. I'd still like to work with someone to tweak components
> and firmware as needed for a holding magnet configuration.
> >
> > Mike
> >
> > ______________________________________________________________
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> >
> >>>> Jordan Spencer Cunningham's GreenKeys Search Tool:
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> >
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>
> > w2hx at w2hx.com
>
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> >>> 1998-to-2001 greenkeys archive:
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> >>> http://comcents.com/tty/greenkeyssearch.html
>
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> Please help support this email list: http://www.qsl.net/donate.html Message
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>
> >>> Jordan Spencer Cunningham's GreenKeys Search Tool:
> https://teletype.net/gksearch
> >>> 2002-to-present greenkeys archive:
> http://mailman.qth.net/pipermail/greenkeys/
> >>> 1998-to-2001 greenkeys archive:
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> >>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
> http://comcents.com/tty/greenkeyssearch.html
>
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