[GreenKeys] Parallel to Current Loop Conversion

[Cory Heisterkamp]

Well Rodger, how's this for an old school solution? : )  
http://en.wikipedia.org/wiki/Teletype_Model_28#mediaviewer/File:Teletype_Model_28_Receiving_Selector.jpg

I appreciate all the feedback, guys. I think I'll pick up some of those UARTS to play with, and Jim's suggestion of tapping into the 33's distributor gets me going. By the same token I would think I'd be able to sample those contacts to latching relays to go the other direction. Fun stuff! -Cory



On Dec 4, 2014, at 7:01 PM, Rodger Casey wrote:

> I got a real kick out of a 40-pin IC package being described as "old school."  I must be older than I fully realize...  :-)
> 
>> On Dec 4, 2014, at 7:55 PM, Jim Haynes <jhhaynes at earthlink.net> wrote:
>> 
>>> On Thu, 4 Dec 2014, Cory Heisterkamp wrote:
>>> 
>>> Before I go and reinvent the wheel, I was wondering if anyone had a proven
>>> old school circuit (no micros) for converting parallel 8-bit data to
>>> ASR-33/35 friendly 110 baud equivalent. This won't be a computer interface,
>>> rather the parallel source will either be switches or relays with an
>>> additional line to 'release' the data when ready.
>> If it's a Model 33 that's involved, note that the keyboard and tape reader
>> contacts are open when they are not transmitting, so you can connect your
>> relay-contact parallel signal to the M33 distributor and then kick it
>> off when you are ready to send a character.  This is the way it was done
>> in the console terminal for the Burroughs B5500 computer, if I remember
>> correctly.