[GreenKeys] Re Current Loop Question

[Carol Fano]

Hi All,

Jumping in with both feet...
As some of you know, I have a KSR 35, which I have been working on restoring. I haven’t done much since spring though.
Can I use low voltage (12-20 VDC) for my loop rather than 120VDC? I only want to convert it to RS232. If I could find the line card, I wouldn’t need the loop...

73,

Carol
> 
> ------------------------------
> 
> Message: 7
> Date: Sun, 27 Sep 2020 19:59:16 -0500
> From: Mike Douglas <deramp5113 at yahoo.com>
> To: GodOfCows <jacobdouglastupper at gmail.com>
> Cc: greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] Current Loop Question
> Message-ID: <AEC1A397-F333-424B-9DF0-2355AC2C76E9 at yahoo.com>
> Content-Type: text/plain;    charset=utf-8
> 
> Considering a 32/33 with a UCC-6 connected across the room to a computer:
> 
> The receive side (data to the printer) clamps the positive side of the loop to less than 0.8v or so above the negative side of the loop. The sender can get by with a very low loop voltage as long as it can source the required 20ma.
> 
> On the transmit side (data out of the teletype), the voltage has to be high enough that the fairly high resistance of the carbon distributor wiper plus the contact resistance of the keyboard, reader, or answerback is not a factor in the receiver?s sense circuit. I?ve never had a problem using 12v for this loop.
> 
> Mike