[GreenKeys] Current loop not providing (enough) current

[Ralph Mowery]

I may have started the booster loop.

I wanted to see how inexpensive and simple it would be to have a loop supply
for those with limited tools or electronic knowledge. 

I found the booster converters on ebay for just a few dollars.  The power
resistor seemed to be the big cost, and any wall cube from about 9 volts up
will work if it has enough current. My 12 volt cube  is only rated for just
over one amp. Most of the parts have screw terminals so all that is needed
is a way to strip the wires and a screwdriver.  

The converters I played with put out about 90 volts which is plenty for a
local loop.  I would use closer to 150 to 200 if going off a radio or had
several printers in the loop.  I found that about 50  volts and lower were
where my 19 started making mistakes off the computer to printer board.

Just out of curiosity I bought a board that you could set for a constant
current,but about 25 or 30 volts was all it was good for.  That board just
would not put out enough voltage and had about a 70%   error rate ,
especially if running off the computer and not  just hand typing one slow
character at a time.

Ralph ku4pt

 

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Jim Cooper
Sent: Saturday, September 21, 2019 12:39 PM
To: Zach Zarzycki
Cc: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current loop not providing (enough) current

On 21 Sep 2019 at 11:37, Zach Zarzycki wrote:

> Well - I have my 26 hooked up though
> the volpe board and have managed to
> get as far as when I type on the
> teletype's keys the terminal window
> on the laptop accurately displays
> what I've punched up. 

I have a couple of comments/suggestions.... 

First off, I don't see why so many are trying 
to use "boosters" and such to make a loop 
supply ...  Use 'real' transformers and power 
supply components -- diodes, capacitors, etc. 
Even if you take 2 'filament transformers' 
( 110v to 6v ) back to back like an isolation 
transformer ...  much more rugged and less 
flaky than voltage "booster" stuff. 

Second, set up your 60mA loop by itself ... 
adjust it for 60mA.  Then put the 26 selector 
magnet in series with the 26 keyboard in series 
with the loop.  Make sure the 26 runs 'closed' ... 
marking.  Type on the keyboard and be sure 
the printer prints on the paper correctly.  Then 
add ONE more part of the circuit at a time, and 
be sure that added part is working properly.  

w2jc


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