[GreenKeys] Fwd: New Teletype Model 28 ASR

[w9ddd at tapr.org]

I meant to send this to the list as well as to Bill. 

John, W9DDD


Begin forwarded message:

> From: "w9ddd at tapr.org" <w9ddd at tapr.org>
> Date: July 28, 2019 at 8:41:57 AM CDT
> To: William Wuttke <wcwuttke at att.net>
> Subject: Re: [GreenKeys] New Teletype Model 28 ASR
> 
> Bear in mind the usual RS232 to 20 mA converter is based on the idea of connecting to a 33.  The 33 by default contains a selector magnet driver.  That isolates the inductance of the selector magnet from the loop, so the LR time Constance is not a problem.  Connecting the RE232 to 20 mA converter directly to the 28 selector magnets will have to deal with the LR time constant.  It probably doesn't have a high enough voltage supply for the 20 mA loop to properly drive the 28 selector magnets.  Of course YMMV.
> 
> John, W9DDD
> 
> 
>> On Jul 27, 2019, at 11:24 PM, William Wuttke <wcwuttke at att.net> wrote:
>> 
>> Hi Paul,
>> 
>> I’m currently using a Model 33 ASR with a HAL ST-8000 which doesn’t have a current loop interface. I made a homebrew 20 ma loop to RS-232 converter using HCPL-4100 and HCPL-4200 optoisolators. I don’t have anything that interfaces with a 60 ma loop. The quickest and easiest thing for me to do is convert the 28 to 20 ma.
>> 
>> 73,
>> Bill
>> KE3BK
>> 
>>> On Jul 27, 2019, at 8:07 PM, Paul Heller <paul0926 at comcast.net> wrote:
>>> 
>>> Glad to hear it  I’m curious why you want to run at 20ma.
>>> 
>>> Paul 
>>> W2TTY
>> 
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