[GreenKeys] Fwd: New Teletype Model 28 ASR

[William Wuttke]

Hi John,

I’ve read articles on the 20 ma vs voltage LR time constant problems problems, but I have to give what I have a try. If it doesn’t work, I’ll have to try something else. In the end, I need to connect the 28 to the ST-8000, one way or another. Experimentation is what makes all this fun. The learning that comes from that helps to keep my mind from growing old.

Bill
KE3BK

> On Jul 28, 2019, at 8:48 AM, w9ddd at tapr.org wrote:
> 
> I meant to send this to the list as well as to Bill. 
> 
> John, W9DDD
> 
> 
> Begin forwarded message:
> 
>> From: "w9ddd at tapr.org <mailto:w9ddd at tapr.org>" <w9ddd at tapr.org <mailto:w9ddd at tapr.org>>
>> Date: July 28, 2019 at 8:41:57 AM CDT
>> To: William Wuttke <wcwuttke at att.net <mailto: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 <mailto: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 <mailto: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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