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

[Mike Douglas]

Harold,

The HM selector is about 55 ohms and the PM selector is closer to 220 ohms.

R11 is only in circuit if the TTY is not plugged into the connector. R11 allows the voltage built up on C1/C2 to decay during marking states.

Yes, AFSK audio goes into a comparator, the output of which then goes to an input capture module to time cycle periods.

Mike

> On Jun 26, 2022, at 11:45 AM, Harold Hallikainen via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> Nice! Why the different values of R2 for holding and pulling magnets?
> Maybe the lower resistance of holding magnet coils in parallel?
> 
> What is the purpose of R11 across the selector magnet?
> 
> It looks like the AFSK input is going to an analog comparator input. Is
> this using period timing to demodulate the AFSK?
> 
> Nice work!
> 
> Harold
> https://w6iwi.org
> 
> 
>> On Sun, June 26, 2022 9:34 am, Mike Douglas via GreenKeys wrote:
>> 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:
>>>>> https://teletype.net/gksearch
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>>>>> 1998-to-2001 greenkeys archive:
>>>>> http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool:
>>>>> http://comcents.com/tty/greenkeyssearch.html
>> 
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> 
> 
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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: http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>>> Randy Guttery's 2001-to-2009 GreenKeys Search Tool: http://comcents.com/tty/greenkeyssearch.html
> 
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