[GreenKeys] Regenerative Loop Driver for Model 15 Teletype

Wed Dec 8 16:28:01 EST 2021

 Hi Gerry,

Yes, I have monitored the current. Current builds to about 40ma at the end of capacitor discharge (about 2ms). Current has decayed to zero in about the same amount of time during the capacitor charge phase.

Mike
     On Wednesday, December 8, 2021, 02:53:05 PM CST, Gerry Block <gblock at sbcglobal.net> wrote:  

 Mike that is a beautiful board. Have you looked at the selector magnet current that your design provides using a current probe??Gerry

Sent from my iPhone

On Dec 8, 2021, at 6:57 AM, Mike Douglas via GreenKeys <greenkeys at mailman.qth.net> wrote:

 You can see what I presently have running here: https://deramp.com/downloads/teletype/Model%2015/loop%20interface%20board/

Mike

     On Tuesday, December 7, 2021, 09:41:41 PM CST, Harold Hallikainen <harold at w6iwi.org> wrote:  

 Very nice! It would be  interesting to see a schematic of the loop keyer.

Harold

On Tue, December 7, 2021 6:51 pm, Mike Douglas via GreenKeys wrote:
> I  have a new 60ma loop driver for the Model 15 (and related units) up and
> running that does not require a high voltage supply, nor does it include a
> switching supply to generate a high voltage. Instead, a regenerative
> approach is used in which the snubber circuit for the selector magnet coil
> captures the energy from the mark to space transition and then dumps that
> energy back into the selector magnet during a space to mark transition.
> This allows operation of the interface board from a 15v power supply
> which, in turn, allows it to dissipate very little heat.
>
> The board provides two 1/4" phone jacks for connecting the printer and
> keyboard cables from the Model 15. Host connections include RS-232 (DB-9
> or DB-25 via RJ14 modular connectors) and a 3.5mm audio jack for
> connecting an AFSK feed (e.g. ITTY). A barrel jack is provided for
> connection of a 15v AC adapter,
>
> The RS-232 host connection uses ASCII at 9600 baud and includes a
> handshake line to automatically throttle the sending computer. With a
> terminal emulator, it's just a matter of turning on the "hardware
> handshake" checkbox. For vintage computers (e.g., Altair, IMSAI, etc.),
> virtually all serial boards bring out the CTS pin of the UART to the DB-25
> and that will throttle the transmitter without any software changes. This
> allows the host computer to use ASCII at a standard baud rate instead of
> having to worry about five bit/45.5 baud support.
>
> Presently, I have ASCII-Baudot translation tables installed for ITA2-TTY
> and USA-TTY. I've also added the ability to generate ASCII keycodes that
> can't be generated by the Model 15 keyboard by defining an escape sequence
> starting with the blank key. The board allows full or half duplex
> operation and also provides a 5-bit pass-through mode (5 bits within each
> byte).
>
> The audio interface demodulates AFSK (presently mark 2125 Hz and space
> 2295 Hz as used with ITTY) and sends the demodulated output directly to
> the printer.
>
> A configuration menu is entered if ESC is pressed on the host side within
> 3 seconds after power-on. The menu allows selection of which ASCII/Baudot
> translation table to use, enabling  a 5-bit pass-through mode, updating
> the firmware, etc.
>
> I will soon be putting up a video on YouTube that shows a Model 15 in use
> as the console for an Altair 8800 computer. This provides a good
> demonstration of the Model 15 as well as the ASCII interface capability of
> the loop driver.
>
> Mike
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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

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