[GreenKeys] USB-teletype adapter with ASR33 question

[epvgk at limpoc.com]

On Tue, Jun 07, 2016 at 04:58:57PM -0400, Lester Veenstra wrote:
> Put a low voltage power supply and current limiting resistor (No need for 130 V in this case) in series with the ASR TX contacts and the USB input.  Set up the voltage/resister for 60 MA and you should be in business.  Before you start, put an ohm meter across the ASR TX contacts and you should see a fairly low resistance.  When typing you should see the resistance go up.

He's using a 33, shouldn't it be 20mA? (the usb adapter won't care, but the tty
might?)

eric

> 
>  
> 
> Lester B Veenstra  M??YCM K1YCM W8YCM
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>  <mailto:lester at veenstras.com> lester at veenstras.com
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> From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Julien Scrofani
> Sent: Tuesday, June 07, 2016 4:29 PM
> To: greenkeys at mailman.qth.net
> Subject: [GreenKeys] USB-teletype adapter with ASR33 question
> 
>  
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> Hi all,
> 
>  
> 
> I bought Eric's usb adapter to link my asr33 tty to a PC.
> 
> As is, I can transfer from PC to the tty but I cannot transmit in the other way, tty toward PC.
> 
>  
> 
> I know that current loops are needed. 
> 
> It works for one way without additionnal power supply, so maybe my 33 has an internal current loop. My problem is I'm not able to determine if it's really the case and I don't how to add one if I need to.
> 
>  
> 
> I have no electronic knowledge at all, sorry if my question is a dummy one !
> 
> Thank you in advance.
> 
>  
> 
> Bests regards, 
> 
> Julien
> 

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